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Products => Test Equipment => Topic started by: torch on September 04, 2015, 06:12:54 am

Title: Inside the new Korad KA3305P linear PSU
Post by: torch on September 04, 2015, 06:12:54 am
Normally I avoid buying lemons by checking things out here first. But I guess this is too new. I decided to take a chance because Korad made things right on the KA3005 design that failed on Dave a while ago. I don't know that I'll ever have a need for it, but I bought the programmable version. It was only $20 more for that option, so what the heck.

It arrived today, and here it is in pictures:

(http://picturehosting.verhey.org/korad/01-Front_panel.JPG)


It comes with a USB cable and one pair of really cheesy leads (also a driver disk, thin manual and power cord, not shown. The manual is better than many, but still Chiglish.)

(http://picturehosting.verhey.org/korad/00-accessories.JPG)

Inside there's a fair bit of empty space. I assume this must be necessary for adequate cooling around that transformer?

(http://picturehosting.verhey.org/korad/02-inside_right.JPG)

(http://picturehosting.verhey.org/korad/03-inside_left.JPG)

The transformer core is about 4-1/2" x 3-3/4" x 3-1/4". Other than that I can't tell you anything about it -- there's no printing on it whatsoever on any side.

(http://picturehosting.verhey.org/korad/04-transformer.JPG)

The power board is behind the transformer, dominated by a giant heat sink and fan. The little board above handles the programming communications, with both serial and USB ports.

(http://picturehosting.verhey.org/korad/05-power_board.JPG)

Each side of the heatsink features a row of four large semiconductor devices well bedded in thermal paste. There's also 3 TO-220 devices with individual heatsinks on the right. They are not secured to the board, relying on the device itself for support. I'm not too happy about that, but other than that the boards seem well made.

(http://picturehosting.verhey.org/korad/06-heatsinks1.JPG)


I'm not sure what exactly these devices are, there's no ID on the chips. 5 of them have 3 terminals, 3 of them have 4 terminals. At a guess, I'd say IGBTs and bridge rectifiers, but I didn't try tracing anything out:

(http://picturehosting.verhey.org/korad/07-heatsinks2.JPG)


The fan blows down on the heatsink. The fins run fore-and-aft, up against the rear exhaust vents. The front of the heat sink has been blanked off with a metal plate to ensure all air goes out the exhaust. The fan is variable speed. It doesn't run at all when no current is flowing and ramps up when the PSU is delivering power. I don't know if I ever taxed things enough to hit full speed, but what I've heard so far is very quiet. (BTW: the beeps when a button is pushed are equally unobtrusive).

(http://picturehosting.verhey.org/korad/08-heasink_shield.JPG)


The brains of the thing are mounted to the back of the front panel. Mostly a whole lot of smd devices, but there's also an unoccupied 4-pin header. Jtag?

(http://picturehosting.verhey.org/korad/09-control_board.JPG)


It comes with binding posts, which I like. The holes are a bit smaller than I'm used to though and they didn't bother to orient the holes in any particular direction on assembly! Personally, I think the holes should be aligned vertically rather than pointing at the adjacent post.

(http://picturehosting.verhey.org/korad/10-binding_posts.JPG)


Fortunately, the posts are secured with screws to the control board (J6 to J17), so it was easy to align them all properly while things were apart. I'm still debating whether or not I should drill out the holes a bit larger though:

(http://picturehosting.verhey.org/korad/11-binding_post_rear.JPG)


Looking at pictures on a website, I did not realize that the footprint was so damn big! It takes up a fair bit of real estate, which as you can see is at a premium in my little corner.

(http://picturehosting.verhey.org/korad/12-footprint.JPG)


So, how does it work?

It seems to be fine with a dead short across the terminals. It survived the "welding test". So hopefully it has whatever improvements that Korad made to the one Dave tested. I don't have a fancy programmable load like Dave, so I tried to load it up with a carbon pile battery load tester. Now, that thing is built to measure hundreds of amps at 12v, not 5 or 10 amps at 30 or 60 volts. The adjustment is just too coarse for any semblance of precision, so my results may not be completely accurate.

That said, I could not get it to deliver more than 4 amps at 62 volts (serial mode*). If I tweaked the carbon pile a touch more, the current jumped to 5.1 amps, but the voltage dropped to 48 volts. A touch more and the current remained at 5.1a while the voltage dropped even further (sometimes down under 2v), so it looks like the current was being actively limited. I'm going to have to find a more suitable load for this test. I had similar difficulties in parallel mode. It will deliver 10.2 amps though.

The fixed 5v channel has an open circuit voltage of 4.997, which drops to 4.927 under a 1 amp load (5 ohm power resistor). The 5 volt channel is always on, unlike the two variable output channels. Both variable output channels are controlled by a single on/off switch. The display shows the set current and set voltage for each when the switch is "off" and the actual delivered values when the switch is "on", unless you are actively changing a value while powering something, in which case it temporarily reverts to displaying the set point.

In serial and parallel modes, channel 1 is slaved to channel 2, so changing the setting of channel 2 automatically changes channel 1 to the same value. Channel 1 cannot be changed independently in those modes. The display behaves a bit differently too: when actively changing the settings, the channel 1 display will continue to show the actual output while the channel 2 display shows the set points.

Changing the setpoints is not quite as simple as twirling a mult-turn pot. First you push the button for the channel you want to change. Then you push the voltage or current knob until the desired digit is flashing, then you turn the appropriate knob to change the digit. The knobs have a nice detent at each change of digit, but can revolve infinitely. As a digit passes 9, the next most significant digit is incremented. So if you are adjusting the left-most digit, the knob is a very coarse adjustment, but the adjustments are progressively finer if you choose to adjust a digit to the right. EG: Adjusting the leftmost voltage digit from 10.81 will increase to 20.81 then 30.81. But if you are adjusting the first digit to the right of the decimal, it will increase to 10.91, 11.01 etc up to 30.91. If you need the full 31 volts, you have to then switch to adjusting the right most digit. Clear as mud?

One other complication: the adjustment mode times out fairly quickly when actively delivering power. Once it times out, you have to go through the whole rigamarole again to continue any adjustments. A good idea in principle, but in practice it would be nice if the delay was a bit longer.

The system is cute, but a bit complicated. It would be easy to accidentally crank up the voltage or current too high for the circuit under test. However, there are both over-current protection and over-voltage protection features. It took me a bit to understand how they work, but they can be thought of as a kind of a customized fuse. You can set a limit for the maximum currents and maximum voltages that each channel can deliver, separately from the normal adjustment. For example, one might set the OVP to 14.5 volts when working on an automotive device so that you cannot accidentally crank the voltage up to a damaging level. If you subsequently try to exceed 14.5 volts, the PSU will shut down. Similarly, you can set current limits. Each channel can have different limits provided you are not in Serial or Parallel mode, in which case the Channel 2 limits apply. (There is no OVP or OCP for channel 3 though).

There is also a "lock" feature that locks out all control panel inputs. It's not necessary to prevent accidentally spinning an adjustment knob, but it could prevent disaster if you bumped a memory button. There are 5 preset memories. Pressing M1 through M5 switches the outputs to the values that were used when that memory was last used. Any subsequent changes while that memory position is active are automatically saved.

The displays are reasonably accurate, to within 0.006v according to my meter. Which has not be calibrated by a lab or anything. It does not go down to 0, despite the display. My uncalibrated meter still showed a few hundredths of a volt which disappears when the On/Off button is pressed. I confirmed voltage was still present by checking for current across the leads.

So in conclusion then,

Pros:
Reasonably well made for the price.
Linear.
3 channels
Lots of available power.
OVP and OCP for those times when you don't want all that power available.
Can withstand short circuits.
Quiet fan. Much quieter than any other fan in the room.
Good cooling path
Nice clear easy-to-read displays
Good tactile feel to the controls.
Multiple memories.
No noticeable heat to the case when loaded.
Binding posts (as opposed to recessed jacks)
Unobtrusive beeps.

Cons:
Very large footprint.
A single set of cheesy leads with a 3 channel PSU?
Complicated adjustment procedure.
Short time-out when adjusting.
Channel 3 not switched
Unknown components when it comes time to repair things.
Some heat sinks not secured to a fixed point.
Did I mention how big it is?

To Do:
Find a more suitable load to test the extremes.
Try out the software and programming capabilities.
Figure out a better place to put it.


*A note for the uninitiated: Serial mode is simply connecting the two channels in series, internally connecting Channel 1 negative to Channel 2 positive. Available voltage doubles. Alternatively, either Channel 1 negative or Channel 2 positive can be connected to the circuit ground, turning the Channel 1 positive into a + voltage supply and the Channel 2 negative into a - voltage supply for things like op-amp circuits. Parallel mode connects the positives together and the negatives together, making a single channel with twice the available current.

Title: Re: Inside the new Korad KA3305P linear PSU
Post by: dom0 on September 04, 2015, 09:28:48 am
You also want to check with a scope if it behaves on power up and power down (little, ideally no, overshoot).
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: nowlan on September 04, 2015, 10:06:19 am
Tell em the price son.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: torch on September 04, 2015, 12:32:08 pm
I'm sorry, I'm new at this  ;)

There is one North American vendor, and his price is $200. However, he offers free shipping if purchased via eBay, unlike purchases through his web store or Amazon presence. Prices may vary elsewhere in the world.

There is no overshoot. There is a momentary pause as it homes in on the final setting.

This is serial mode, 31v setting (so, 62v), no load, power on:
(note: by "power on", I mean via the On/Off key to turn power on to Channels 1 and 2, not powering on the main power for the whole unit)

(http://picturehosting.verhey.org/korad/60v.bmp)



Here is channel 1, 31v, no load, power on:

(http://picturehosting.verhey.org/korad/31v.bmp)



Channel 1, 1v, no load, power on:

(http://picturehosting.verhey.org/korad/1v.bmp)



Channel 1, 1v, across 5 ohm power resistor, power on:

(http://picturehosting.verhey.org/korad/1v_loaded.bmp)



Channel 1, 1v, across 5 ohm power resistor, power off:

(http://picturehosting.verhey.org/korad/1vload_off.bmp)



Etc. etc. They're all the same so I didn't bother with all the nonsense of saving and uploading. And there's no momentary spike even setting the time base to 2nS. What you see above is a fair representation.

(I did, however, fix the glitch in my first post that prevented the last image from loading. Now you can see the footprint next to some other equipment for comparison.)




Title: Re: Inside the new Korad KA3305P linear PSU
Post by: torch on September 04, 2015, 12:46:09 pm
Oh, and I'm still digging around for that perfect load. SWMBO's hair dryer gets throttled back to 42v on high and only draws 3.6 amps at 62v on low...
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: Kleinstein on September 04, 2015, 05:51:48 pm
The transformer does not seem to be large enough to deliver the full power for an extendet time. This would require something like a 500-600 VA transformer. This one looks more like 250 VA, maybe 350 VA.  Also the elcos look rather small for 5 A. So the full current may not be available at the full current. Likely it would be better to have a maximum current level in the 3 A range to be save.

Also I can't see any fuses and no thermal sensor at the transformer.  At least a fuse on the primary sinde could be added relatively easy.

Ohterwise it least looks ok. The ramps on power on look a little strange, but not bad.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: Hydrawerk on September 04, 2015, 06:33:03 pm
The fan should blow directly from outside, as you can see on your home PC.

And the total output power is not specified. http://koradtechnology.com/en/cp-26.html (http://koradtechnology.com/en/cp-26.html)
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: torch on September 04, 2015, 06:34:05 pm
There is a 20 amp fuse in the mains socket. It is possible that there is a fuse inside the transformer itself, I've seen that before, but there is no outward sign of it and there certainly is no external thermal sensor attached to the transformer.

Elcos? Electrical connections?

It's funny you mention 3 amps. They also make a 3 amp version that is outwardly very similar. And we all know how companies like to use the same components in similar models to save on inventory expenses. I think it probable that the 3 amp version is differentiated from the 5 amp via software and a Jtag interface. Likely the only difference between the programmable and non-programmable versions too. (Well, that and the little communications board tacked on this one.) It wouldn't really surprise me if an engineer figured out he could squeeze 5 amps from the transformer by shaving all safety factors to the bone. Let's face it: this thing sells for $200.

It is replacing my little home-made 1 amp supply. Most of my projects to date are at half the voltage or less. I don't foresee needing a constant 5a 30v supply for any extended length of time, I just figured it was better to have the capacity and not need it than to need it and not have it. That said, there is nothing mentioned in the manual about a duty cycle or other restrictions and it comes with a 1 year warranty. So if it burns up running it at full power and 100% duty cycle in that time, it's their problem.

Title: Re: Inside the new Korad KA3305P linear PSU
Post by: dom0 on September 04, 2015, 06:40:30 pm
Elcos? Electrical connections?

electrolytic capacitors
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: torch on September 04, 2015, 06:52:45 pm
And the total output power is not specified. http://koradtechnology.com/en/cp-26.html (http://koradtechnology.com/en/cp-26.html)

No total as such, but the specification sheet (http://www.sra-shops.com/docs/srasolder/datasheet/datasheet_ka3305d_ka3305p.pdf) says "0-30v, 5a * 2"

Of course, that's the same specification sheet that says it's only 260mm deep, and you all can see how that worked out for me. They only missed being accurate by 100mm or so. (claimed 220 x 156 x 260 vs actual 250 x 140 x 360)
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: FlyIt! on September 05, 2015, 12:26:55 am
Hey Torch,

Thanks for being an Early Adopter on this one. 
I've been waffling on this one for the last two days, but your review has pushed me over the edge.  Ordered one just now.

The quirks you pointed out are duly noted (again, Thanks!) but all things considered, the Korad KA3305P certainly seems to offer a lot for the $'s. 

Personal 'clincher' for me?  I couldn't find any other supplies that offered the USB (and RS232) control and logging options, without going to crazy dollars.  I need these features for some upcoming test/optimization/validation tasks, which ideally can be automated.  At the price, I see ways to save myself many, many hours of hands-on testing and logging.

Back to your review: I do hope they give us a firmware update option to allow longer timeouts on output adjustments.  As you described the 'flow' and timeout, that could be a bit annoying (or potentially "Magic-Smoke-releasing"!).

Thanks again!
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: torch on September 05, 2015, 02:19:26 am
Personal 'clincher' for me?  I couldn't find any other supplies that offered the USB (and RS232) control and logging options, without going to crazy dollars.  I need these features for some upcoming test/optimization/validation tasks, which ideally can be automated.  At the price, I see ways to save myself many, many hours of hands-on testing and logging.

I played very briefly with the software this evening. There's two modes, one a virtual control panel with separate knobs for voltage and current for each channel (ie: 4 knobs) that can just be "turned" with the mouse at any time. Plus a virtual version of all the other buttons. The second mode executes a programmed sequence of voltage/current settings for both channels. IIRC, you can change the start and stop, duration and also the number of loops. It all seemed to work correctly -- I didn't have a load on things but the relays clicked and clacked and the displays changed to reflect the virtual display.

There's a graph of each channel running alongside the interface window, a logging on/off "switch", and a file-folder icon to set the file path. The graphs jumped around each time the settings were changed -- either manually or as the sample default program executed.

For some reason, the software doesn't like the resolution I'm running on that old laptop. Or maybe it doesn't like Win XP. Some of the programming related text boxes are crowded and hard to use, and I can't resize the windows. I need to do some tinkering there, maybe try it on my Win 7 laptop.

I was actually kind of surprised it installed on XP, considering this is a "new" product. I'm guessing it's left-over software. Don't hold your breath waiting for firmware upgrades if that is the case!

Oh, and I don't think it's a native USB port. I think it's a serial port with a USB to serial adapter built-in, based on the drivers I saw it installing. On the plus side, there were no glitches or problems with the installation.

That's as far as I got. I haven't even looked at the PDF guide on the cd yet -- I have 3 very active grandsons sleeping over tonight, so Poppa's focus has been temporarily redirected.  ;)  But hopefully it will do what you need.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: torch on September 05, 2015, 02:55:40 am
Update: the supplied software is not by Korad. Apparently they licensed it from "National Instruments" and it's called "LabVIEW 2014". www.ni.com/labview (http://www.ni.com/labview). And it seems to run fine on this Win7 laptop.

There's also a PDF list commands and syntax in case you want to write your own scripting. No idea how to do that, through a terminal emulator perhaps?
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: Salas on September 05, 2015, 05:46:49 am
Good value for money new Korad PSU package. Unnecessarily bigger than its contents as you say though. I wonder, would it keep a straight enough rail line on the scope at 200mV per division resolution AC coupled when powering a high current dynamic load? Not necessarily a punishing pulse test. More life like things like a loaded audio power amplifier pulling strong amperage on a few kHZ sinewave for instance. We haven't seen such testing even on Dave's usually more expensive PSU models videos I think.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: torch on September 05, 2015, 01:31:56 pm
Good value for money new Korad PSU package. Unnecessarily bigger than its contents as you say though. I wonder, would it keep a straight enough rail line on the scope at 200mV per division resolution AC coupled when powering a high current dynamic load? Not necessarily a punishing pulse test. More life like things like a loaded audio power amplifier pulling strong amperage on a few kHZ sinewave for instance. We haven't seen such testing even on Dave's usually more expensive PSU models videos I think.

Sounds like a great test. I'm certainly willing to try but unfortunately my days of loud music are long past.

Hmmm. I do have an ARB function generator (hantek 3x25) and a few big IGBTs (g4pc40u). And some old transformers for a load. It should be possible to construct a simple amplifier around those, right? I am not an electrical engineer so I would need some help designing said simple circuit. Or some alternative ideas.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: Salas on September 05, 2015, 04:38:34 pm
Probably doable, but to avoid the hassle maybe there is some old receiver around? Connecting on one channel's rails fuses after disconnecting its own PSU, no big reservoir capacitors aid to the bench PSU ;), and some cement resistors combo 5-10 Ohm 50W dummy load hanging off its speaker output posts should run the test without needing a loudspeaker driven to some earsplitting SPL.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: torch on September 05, 2015, 09:01:32 pm
The old receiver is a tube powered floor model radio. Most of the energy goes into heating the tubes -- not really very dynamic. Everything else is pretty low-powered around here.

I'll see if I can figure something out.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: mos6502 on September 05, 2015, 09:10:03 pm
A bunch of old car headlight bulbs should do the trick. Wire them in parallel/serial as needed. Just keep in mind they're non-linear and will draw about 10 times the normal current for a few milliseconds while they heat up.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: torch on September 05, 2015, 09:40:32 pm
The car headlights won't be very dynamic to do the ripple test that Salas asked for.

Funny you should mention light bulbs though. I had a half-dozen new-in-box H3 bulbs that I bought on clearance for $1 or two each a few years ago. On my first attempt to load test I hooked them up to the Korad and they drew a heck of a current, but no light output. What the heck?  I checked and rechecked connections before I discovered that every one of them was shorted out. I think the wires on each are pinched by the metal housings. No wonder they were on clearance.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: mos6502 on September 05, 2015, 09:48:47 pm
The car headlights won't be very dynamic to do the ripple test that Salas asked for.

Of course, you have to switch them on and off using your IGBTs. The good old NE555 should do the trick. 50Hz would be a good frequency. This will keep the bulbs hot so their resistance should remain fairly constant.

Funny you should mention light bulbs though. I had a half-dozen new-in-box H3 bulbs that I bought on clearance for $1 or two each a few years ago. On my first attempt to load test I hooked them up to the Korad and they drew a heck of a current, but no light output. What the heck?  I checked and rechecked connections before I discovered that every one of them was shorted out. I think the wires on each are pinched by the metal housings. No wonder they were on clearance.

You're better off collecting a bunch at a junkyard. You can usually get them for free. And you'll know most of them will be working. Oh, and also take the bulb sockets while you're there.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: Salas on September 05, 2015, 10:00:44 pm
You think 50HZ will be enough to show if the loop speed of the lab PSU is slow or decent enough though?
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: Salas on September 05, 2015, 11:04:28 pm
I'll see if I can figure something out.

  8) http://gpete.blogs.keysight.com/2012/03/building-electronic-load-with-general.html (http://gpete.blogs.keysight.com/2012/03/building-electronic-load-with-general.html)
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: wagon on September 05, 2015, 11:31:46 pm
That looks similar to the 'Tenma' unit I bought from Element14 a couple of months back.  Mine looks like two 'single' supplies, side by side.  I don't think it has a USB interface.  It works OK, and can deliver the rated load (60V at 5A or 30V at 10A) for a reasonable time.  I should pull it apart for the giggles and look inside.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: torch on September 07, 2015, 04:48:09 am
I found that five 100w "rough service" drop light bulbs in parallel draws 2.64A @ 62v indicated (PSU in series mode, 61.95v measured at the output terminals). I didn't have any luck using the IGBT as a switch (got the bulb output to oscillate slightly @ 1 hz) though.

No chance of overshoot with this load:

(http://picturehosting.verhey.org/korad/2_4a61_95v.bmp)



The ripple looks pretty bad in that shot, but that's just the screen resolution. Here's the ripple at the same load:
(http://picturehosting.verhey.org/korad/ripple2_64.bmp)

Those two bigger blips almost 200mV P-P about 8uS apart are regular and recurring.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: torch on September 07, 2015, 05:17:55 am
Nevermind. Those blips must be EMF from something. They're everywhere, on both channels:

(http://picturehosting.verhey.org/korad/ripple2.bmp)

(http://picturehosting.verhey.org/korad/ripple3.bmp)



Even with everything but the scope shut off:

(http://picturehosting.verhey.org/korad/ripple4.bmp)

Title: Re: Inside the new Korad KA3305P linear PSU
Post by: torch on September 07, 2015, 05:52:34 am
Not quite what you asked for, more like "a punishing pulse test", but instead of using the on/off button, here I left the PSU on, made contact with then dragged a wire across a coarse file to repeatedly break the circuit. There's an interesting initial brief voltage spike before it ramps up as the bulbs start glowing. Because the load is inductive? Because the resistance increases dramatically as the bulb starts to heat up?

(http://picturehosting.verhey.org/korad/file1.bmp)
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: Salas on September 07, 2015, 08:53:49 am
It can't recover so fast to hold a resemblance of a DC line on that. Using the file on a PSU rings a bell but I can't recall exactly. Was it some guru like Bob Pease or Jim Williams who did it first? Good it did not break something. At least now you know its tough. Money well spent.
Hmm... How a classic linear chip like 78XX, 317 etc. would react when dragged along that file for a load it could bear? That could give some kind of scaled down screenshot comparison.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: dom0 on September 07, 2015, 09:43:52 am
How a classic linear chip like 78XX, 317 etc. would react when dragged along that file for a load it could bear? That could give some kind of scaled down screenshot comparison.

Not much, as stability is mostly an issue with "discrete" (i.e. op amp based) PSUs, while the integrated emitter-output regulators are very stable (they don't have a lot of loop gain to begin with and their fT is in the region of 500-1000 kHz). So output waveform will mainly depend on the output capacitor.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: george graves on September 07, 2015, 11:08:34 am
Can't say I'm a fan of that user interface.  Too bad they didn't make more room for it.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: torch on September 07, 2015, 12:28:08 pm
Using the file on a PSU rings a bell but I can't recall exactly. Was it some guru like Bob Pease or Jim Williams who did it first?

I can't say I know of the file test being applied to a PSU. However, it's certainly not original to me: it is an old trick for down-and-dirty testing of automotive ignition coils. Scrape the primary wire along a coarse file and look for a series of sparks jumping a gap tester attached to the secondary.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: Salas on September 07, 2015, 02:32:46 pm
How a classic linear chip like 78XX, 317 etc. would react when dragged along that file for a load it could bear? That could give some kind of scaled down screenshot comparison.

Not much, as stability is mostly an issue with "discrete" (i.e. op amp based) PSUs, while the integrated emitter-output regulators are very stable (they don't have a lot of loop gain to begin with and their fT is in the region of 500-1000 kHz). So output waveform will mainly depend on the output capacitor.

I would expect them classic chips steadier too. Maybe torch has one around to drag on the rough file. Is such a bench supply relying just on op-amps or an MCU controls the loop more likely?
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: Salas on September 07, 2015, 02:40:03 pm
Using the file on a PSU rings a bell but I can't recall exactly. Was it some guru like Bob Pease or Jim Williams who did it first?

I can't say I know of the file test being applied to a PSU. However, it's certainly not original to me: it is an old trick for down-and-dirty testing of automotive ignition coils. Scrape the primary wire along a coarse file and look for a series of sparks jumping a gap tester attached to the secondary.

So that testing has roots in automotive practice. Interesting. I must have read something in the past about it for an electronics PSU  torture test also. It could have migrated by some car tampering electronics engineer.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: torch on September 07, 2015, 03:19:17 pm
It could have migrated by some car tampering electronics engineer.

Would have to be an old engineer -- someone who was around in the days of points and condensers...
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: dom0 on September 07, 2015, 03:22:01 pm
How a classic linear chip like 78XX, 317 etc. would react when dragged along that file for a load it could bear? That could give some kind of scaled down screenshot comparison.

Not much, as stability is mostly an issue with "discrete" (i.e. op amp based) PSUs, while the integrated emitter-output regulators are very stable (they don't have a lot of loop gain to begin with and their fT is in the region of 500-1000 kHz). So output waveform will mainly depend on the output capacitor.

I would expect them classic chips steadier too. Maybe torch has one around to drag on the rough file. Is such a bench supply relying just on op-amps or an MCU controls the loop more likely?

MCU control loop would be insanely slow and unreliable. There are some very high power / special purpose SMPS which use DSPs for the control loop, though.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: Kleinstein on September 07, 2015, 07:32:57 pm
The linear regultor is done analog, the µC just gives the setpoint and might give a controled ramp after power on. A µC might be used to controll the relays and the fan.

The reaction to this very rough test looks OK, but not very good - there is one spike going noticable higher than normal voltage. The funny spike at the beginning seems to be part of the normal way of switching from CC to CV.  So having short pulse of high current might be a problem for this regulator. This might even leed to overheating of the transistors, as the relays are not very effective with such dynamik loads.

For stability testing there are usually three critical cases:
1) having a low loss capacitor in the 10 µF range at the output and essentially no load. Internal Load might vanish at vry low voltage, so something like 50 mV might be the most critical volatge. This might give istability at high frequency (e.g. 100 kHz), especially if the output cap is small.
2) same as befor, but at a high current from an more or less ideal current sink. This might be rather difficult to build.

3) having a large low (as low as possible) ESR cap of some 1-10 mF and large load steps, especially down from a high current (but not limiting) to essentially 0 current. Here a manualy opening contact migh be enough, as reaction is likely rather slow in the ms range.



Title: Re: Inside the new Korad KA3305P linear PSU
Post by: torch on September 07, 2015, 08:08:02 pm
The reaction to this very rough test looks OK, but not very good - there is one spike going noticable higher than normal voltage.

Yes, the worst spike appears to be about 5v (8%), bearing in mind the low resolution of the screen on my hobbyist-level Rigol scope. There's also two lesser spikes, apparently about 2-2.5v.

Frankly, I suspect there were more that just weren't captured given the time base.

Quote
The funny spike at the beginning seems to be part of the normal way of switching from CC to CV. 

That makes sense. I didn't think of that.

Maybe over the winter I can try your three stability tests. At the moment I don't have an ideal load nor do I have any really large capacitors sitting around. Out of curiosity, how much more stable would one expect a professional grade PSU to be, and how important is it to a hobbyist or student on a limited budget?

Title: Re: Inside the new Korad KA3305P linear PSU
Post by: Salas on September 07, 2015, 10:15:37 pm
The linear regultor is done analog, the µC just gives the setpoint and might give a controled ramp after power on. A µC might be used to controll the relays and the fan.

The reaction to this very rough test looks OK, but not very good - there is one spike going noticable higher than normal voltage. The funny spike at the beginning seems to be part of the normal way of switching from CC to CV.  So having short pulse of high current might be a problem for this regulator. This might even leed to overheating of the transistors, as the relays are not very effective with such dynamik loads.

Could the MCU be controlling the CC/CV transition also and its speed having something to do with the magnitude of such a spike in your opinion?
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: torch on September 08, 2015, 03:34:15 am
The funny spike at the beginning seems to be part of the normal way of switching from CC to CV. 

If that was it, then the sudden in-rush plays a role too. Turning down the current 10mA to force the switch from CV to CC or vise-versa results in a smooth transition. Here's a sample that switched it from CV to CC and triggered a relay to click at the same time:

(http://picturehosting.verhey.org/korad/cv_to_cc.bmp)


The transitions where the relays kick in are quite smooth going up too. This is increasing the voltage by 0.1V, triggering a relay:

(http://picturehosting.verhey.org/korad/vrelay.bmp)

(both under load -- my 5 parallel lightbulbs)

Title: Re: Inside the new Korad KA3305P linear PSU
Post by: Kleinstein on September 08, 2015, 09:00:08 am
Stability (that is protection from oscillation and well behaved reaction to load changes) is something every PSU shoud offer. This a mainly a question of following basic rules. This about finding the rigth size for the nF range caps nothing that costs a lot of money per unit. It gets more difficult if the PSU is trying to regulate very fast. So there a cheap PSU can be very good in this respect, and a high end PSU that tries to push the limits speed wise is likely to be worse in this respect.

Switching from CC to CV mode is a slightly different thing. This includes nonlinear effects. In control theory the problem is called wind up - easy to solve in a digital regulator, but quite complicated analog. So here well testet high qualitiy PSUs can be expected to be better. At least there should be not complete desaster.  As comlete tests are difficult, however there still is a chance to find a bad one from HP and good chinese one.
Somehow the shape of the peak when changing CC to CV looks very much as I expect from a standard circuit. So it might even be a hint that stability is likely good.

The real drawbacks of these cheap chinese PSUs is the thermal design: they are made to deliver much power at low cost. Here less safty marging saves costs and thus things get hot right to the limit. Similar main filter caps are rather small as they are expensive parts. So some units that get the smaller ones show rippel at the upper limit.  For me this PSU looks good up to about 3 A. A more reputable brand might sell such a supply with just the upper current limit reduced and some fuses added.  So if you know and respect the limitations such a cheap PSU is not hat much inferior to brand named one.

One other point the chinese save some money is to pots / DACs. This might be the reason for the strange jigged shape on startup. Instead of a good DAC there may be a ADC / DAC loop to set the voltage.

Besides problems with constant high power, the other type of overload, might appear with dynamic loads. This is because the relays are slow, and some ealier stages might get hot as well. Here more reserve helps, but using relays to switch taps can not cope well with highly dynamic loads. So even a HP unit might fail or at least stop with overtemperature error. So the file test is allready pushing the limits of such a supply.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: Salas on September 08, 2015, 12:15:46 pm
Solid state relays are out of the question?
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: Kleinstein on September 08, 2015, 05:33:09 pm
Solid state relais have a relatively large voltage drop. So they are OK at 110 V or 230V, but not that good at 12 V. Switching at AC also has a second problem: the filter caps have to charge, and this gives quite some current spikes.

If mechanical relays are not wanted SCRs are a real alternative. Old school, but less voltage drop than solid state relays, as the can also replace a diode.

The other alternative is doing switching an the DC side  in a class G like output stage. Slightly more diode drop, but as changeover can be very fast there is no need for a worst case reserve for ripple etc.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: torch on September 09, 2015, 05:16:02 am
I have found a serious bug:

If the M4 button is held down for about 2 seconds, the PSU turns on Channel 1 and Channel 2 and starts randomly changing the voltage of one or the other channel (usually Channel 2). While this is going on, the other channel displays 0.000 volts and 0.000 amps, but may be outputting power despite the display. The only way to get out of this is to power down the PSU.

The on/off button will turn off the outputs, and the voltages will drop to 0.000v but the random voltage changes will resume as soon as the outputs are turned back on. Also, the outputs may or may not be "on" when the PSU is powered back up the next time (outputs should be "off" when the PSU is powered up), however all controls will function normally.

This behaviour will occur regardless of the keypad lock. No other keys will function with the keypad locked, but leaning on M4 for 2 seconds will still result in this bizarre behaviour.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: torch on September 09, 2015, 06:05:07 am
Speaking of bugs, the programming software is full of them.

First, the manual gives specific directions about what cable should be used for serial communications and how to use a terminal program to send commands. As I mentioned earlier, it also comes with a virtual panel and scripting software to control it via PC. It can execute a script and log the results. What came with it installed without any hassle and at first glance,, appeared to be working correctly with the exception of a screen resolution issue when running on an old XP machine. (the work around for that on my machine is to set the resolution to 800x600, apply, then restore the resolution. That resizes the window properly thereafter)

Well, things sort of work. The pretty graphical interface works, except it does not change the memory storage location on the PSU, it simply lets you have a second set of independent memory buttons, resident in the computer. Voltage changes are truncated at the decimal point. For example, 7.77v sets the PSU to 7.00v. Also, despite the real-time graphs of voltage and current for each channel, it seems to be logging only one of the channels. I suspect #1 but haven't verified that.

So I decided to try the terminal route. I still haven't figured out the serial port connection but either it's dead or maybe requires a null modem cable (manual shows straight pass-through). I did finally successfully communicate through the USB cable to the virtual Serial-USB adapter installed in the PSU itself.

The manual suggests MTTTY is suitable. It is not. Neither is  Terminal, Hyperterminal  and a host of others that do not send data until "enter" is pushed. The only way I could communicate manually is with RealTerm. Fortunately its open source, available at Source Forge. After selecting the correct port, and opening it, I could send commands via RealTerm's Send tab. 

The keyboard locks automagically when the USB cable is connected. The keyboard lock can be overidden manually at the keypad, but not in software that I could see.

Most of the commands will work despite the keyboard lock. Except the memory recall and memory store commands. That explains why the memory buttons are independently duplicated in software.

What is needed here is some decent software to replace the crap that came in the box. The capabilities are there in the machine, but accessing them is not.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: torch on September 09, 2015, 01:02:36 pm
Here is a short video showing the M4 bug:

http://picturehosting.verhey.org/korad/Korad_M4_bug_conv.flv (http://picturehosting.verhey.org/korad/Korad_M4_bug_conv.flv)

(Sorry for the separate link. I'm not sure how to embed a video here.)
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: torch on September 09, 2015, 03:45:54 pm
Voltage changes are truncated at the decimal point. For example, 7.77v sets the PSU to 7.00v.

I confirmed this behaviour on a  Win7 laptop this morning, so it's not because I have an old XP machine on the bench.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: torch on September 11, 2015, 05:52:47 pm
Here is a short video showing the M4 bug:

http://picturehosting.verhey.org/korad/Korad_M4_bug_conv.flv (http://picturehosting.verhey.org/korad/Korad_M4_bug_conv.flv)

Update: I contacted the US distributor with a description of the problem and the above video link, but so far I've heard nothing but crickets. I have now submitted it to Korad via a feedback form on their website. We'll see what happens, but I imagine they've all gone home for the weekend by now.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: torch on September 19, 2015, 05:14:46 am
Update:

The US distributor advises that Korad has fixed the problem, they have the fix, and they have tested the fix.

The bad news is I have to send my unit back for the repair. For some reason it can't be just e-mailed and uploaded by me.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: Kleinstein on September 19, 2015, 11:04:56 am
The bug ist likely a software error. But the powersupply may not have the option to do software update vial USB. In addition they may not want to give away there software without the small amount od protection of the µC - so they may preferre to pay postage for the few early users that realy care about the bug.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: torch on September 19, 2015, 01:06:22 pm
In addition they may not want to give away there software without the small amount od protection of the µC - so they may preferre to pay postage for the few early users that realy care about the bug.

That makes the most sense -- they are afraid the firmware will eventually get into the hands of potential clones.

$5 says it's roots are open source though  ;)

Anyway, it's good to hear that they have produced a fix, even though it's a PITA to ship this thing back.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: Hydrawerk on September 19, 2015, 03:32:52 pm
Here is a short video showing the M4 bug:

http://picturehosting.verhey.org/korad/Korad_M4_bug_conv.flv (http://picturehosting.verhey.org/korad/Korad_M4_bug_conv.flv)

(Sorry for the separate link. I'm not sure how to embed a video here.)
Just paste the youtube link.
Code: [Select]
https://www.youtube.com/watch?v=g94mpom2Ahs

https://www.youtube.com/watch?v=g94mpom2Ahs (https://www.youtube.com/watch?v=g94mpom2Ahs)
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: Pinkus on September 19, 2015, 03:40:27 pm
you may ask them to send you a new main board with a new software release installed instead. This would be the least expensive way for everybody.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: torch on September 19, 2015, 06:02:01 pm
Just paste the youtube link.

I don't do youtube anymore. I closed down my account when Google tried to force me into signing up for a bunch of stuff I didn't want. The video is hosted by me. But thanks for the thought.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: torch on September 19, 2015, 06:03:34 pm
you may ask them to send you a new main board with a new software release installed instead. This would be the least expensive way for everybody.

I'll ask.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: torch on September 20, 2015, 06:04:07 pm
I asked, and was surprised to receive a reply on a Sunday. Sounds like they are willing to do a board swap. The guy who is handling this is on vacation this week, but they will have him contact me to hammer out the details when he gets back next week.

I have to say that Korad (and their distributor) seem to be standing behind the product.

I also asked about the maximum output rating. Their response was
"It depends on the fan and heatsink inside the unit. As long as that fan keeps going you could theoretically run all three channels at max indefinitely, but the fan is the weak point. "

This would seem to confirm Klienstein's earlier comment:

The real drawbacks of these cheap chinese PSUs is the thermal design: they are made to deliver much power at low cost. Here less safty marging saves costs and thus things get hot right to the limit.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: mos6502 on September 20, 2015, 06:53:38 pm
I also asked about the maximum output rating. Their response was
"It depends on the fan and heatsink inside the unit. As long as that fan keeps going you could theoretically run all three channels at max indefinitely, but the fan is the weak point. "

Hmm. Usually the weak point is the transformer. Because copper is expensive. So if manufacturers want to skimp, they just use a smaller transformer and rely on airflow to keep it cool.

Another trick is to use a very small filter cap and higher transformer output voltage and rely on the pass element to dissipate the extra heat. The small filter cap keeps the RMS current low and allows the transfomer to deliver more power. This is also why you should never "upgrade" the filter caps in a linear supply with larger ones.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: torch on September 20, 2015, 07:25:27 pm
Another trick is to use a very small filter cap and higher transformer output voltage and rely on the pass element to dissipate the extra heat.

The filter caps are 6800µF each. If I did the math right, that should work out to 3% ripple with a load of 10A at 30v. From what I've read, that's a reasonable figure for a linear supply. Or would you consider that "small" for the application?
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: mos6502 on September 20, 2015, 08:06:06 pm
Another trick is to use a very small filter cap and higher transformer output voltage and rely on the pass element to dissipate the extra heat.

The filter caps are 6800µF each. If I did the math right, that should work out to 3% ripple with a load of 10A at 30v. From what I've read, that's a reasonable figure for a linear supply. Or would you consider that "small" for the application?

6800uF for 5A is fine. I was merely explaining what some Wun Hung Lo manufacturers do. The Korads actually seem to be well designed.  :-+
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: bitseeker on September 21, 2015, 03:42:41 am
I remember seeing this new model on pre-order for a while. Thanks for the teardown photos. What all changed from the prior triple-channel model?
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: torch on September 21, 2015, 10:06:00 am
I remember seeing this new model on pre-order for a while. Thanks for the teardown photos. What all changed from the prior triple-channel model?

Not a lot, as far as ripple/regulation specifications go. The 3-channel 3amp predecessor was called KA3003D-3S. It looked just like they took two single-channel supplies and stuck them in a double-wide case. They even retained separate on/off buttons and separate keyboard lock buttons for channel 1 and channel 2. There was no obvious serial/parallel operation, (although one review I read suggested it was possible, so it may have been added mid-production). It had separate fans and reviews I read mentioned they are running all the time and a bit on the noisy side.

Supposedly there was a KA3005P-3S version providing 5 amps and programming capability, however that may have been vapourware as I never did find one actually for sale anywhere.

This one seems better integrated (to me) and perhaps more importantly, available.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: Kleinstein on September 21, 2015, 07:49:32 pm
As transistors a cheap today, the real weak spot is often the transformer - but sometimes even a few cents saved on the output transistors are still tempting.

Having a rather small filter cap helps to reduce the current peaks, but you than also need more reserve in voltage. So you can not gain that much by reducing the cap size, unless you risk that ripple might be apear at the output at high voltage and high current. This might only happen if the caps are at the lower end (tolerances are quite large) or mains voltage is less than nominal.
Using a relay to switch transformer taps also calls for the cap not to be very large, as this gives extra current peaks when swithing to a higher voltage.

Transformers can stand more than nominal load for quite some time. They get hotter however and thus age faster. Having the fan might also help to ensure cooling of the transformer.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: torch on September 21, 2015, 08:29:35 pm
I wonder what the effect would be to stick a nice big aluminium CPU heatsink right on the transformer core? Maybe even with it's own fan? Would it help keep the transformer cooler? Would it somehow interfere with the magnetic flux of the core?
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: bitseeker on September 22, 2015, 07:46:51 am
It might help, just depends how quickly the heat can be dissipated. For a large transformer, the surface may not overheat, but the interior still might.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: Kleinstein on September 22, 2015, 03:47:24 pm
The heat in the transformer comes mainly from the windings. So cooling the core will help a littel, but not that much.
At least it will not interferre with the normal magentic flux. However still some care may be needed, not to cause eddy currents because of eletrical contact to more than one sheet of the core.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: torch on September 28, 2015, 03:31:40 pm
Update: it's first thing Monday morning and the guy who is handling this must be back from his vacation because he sent me a message that they are packaging up a replacement board with instructions on swapping it out and it will be in the mail in the next day or two.

Title: Re: Inside the new Korad KA3305P linear PSU
Post by: bitseeker on September 29, 2015, 04:51:00 am
Although issues have come up with Korad power supplies, the manufacturer is quite fast with fixes. Korad and SRA are pretty responsive and flexible with rectification too, which is good to see. If I didn't already have plenty of vintage power supplies, I'd probably get one of these triple-channel ones.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: torch on October 15, 2015, 05:22:02 am
The replacement board arrived in the mail today (but postmarked October 6).

The new one is on the right, beside the original. They look identical, right down to the funny twist to the crystals.

(http://picturehosting.verhey.org/korad/websized/Replacement_board.jpg)

The M4 bug is fixed, but I found another, minor bug. I'm not sure if it was always there and I just missed it, or if it was introduced with this latest firmware. It happens in Serial mode only. When Serial is selected, the current limit is displayed as 0.000 (both channels). When setting the current limit (ie: press CH2 twice, so a digit flashes) the current limit is displayed temporarily. When setting either OVP or OCP (ie: press and hold OCP for 2 seconds) the OCP set point is displayed. When the output is turned on, the actual current is displayed.

The current setpoint is properly displayed when the output is off in both Parallel mode and Independent mode.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: torch on October 20, 2015, 01:58:53 am
I still haven't figured out the serial port connection but either it's dead or maybe requires a null modem cable (manual shows straight pass-through).

Ok, I was wrong and the serial port works with a pass-through cable as described in the manual.

However, I still can't get a terminal program like hyperterm or MTTTY to work, as they don't send the command until "Enter" is pushed and pushing "Enter" adds a CR character. The Korad ignores any command with an appended CR. The only way I can make this work is through the Send tab of Realterm, which sends the command without a CR or LF when you hit the Send ASCII button. 

The reason I could not get the serial port to respond before was a classic PEBKAC: I set the port speed to 9600 in the port tab in Realterm, but did not realize it doesn't take effect until you hit "Change" -- despite the big green checkmark on the Change button. Doh!

I did finally successfully communicate through the USB cable to the virtual Serial-USB adapter installed in the PSU itself.

It's too bad the supplied software is so buggy. I can see where the programming and logging features could be real handy. What I need now is a Mechatrommer: someone with the skills to create a decent software interface!
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: Messtechniker on October 20, 2015, 05:34:42 am
It's too bad the supplied software is so buggy. I can see where the programming and logging features could be real handy. What I need now is a Mechatrommer: someone with the skills to create a decent software interface!

Why not roll your own with this:
http://www.abacom-online.de/uk/html/profilab-expert.html (http://www.abacom-online.de/uk/html/profilab-expert.html).

For an example I programmed, see here:
https://www.eevblog.com/forum/projects/building-your-own-voltage-reference-the-jvr/?action=dlattach;attach=177041;image (https://www.eevblog.com/forum/projects/building-your-own-voltage-reference-the-jvr/?action=dlattach;attach=177041;image)
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: Gall on October 20, 2015, 01:15:21 pm
Ok, regarding the bugs, it is possible to replace the MCUs with something else with our own program? I bet these funny chips with "Korad" marking are nothing else as ATmega or MCS-51, so it shouldn't be hard to find a pin-compatible replacement.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: torch on October 20, 2015, 01:42:12 pm
Why not roll your own with this:
http://www.abacom-online.de/uk/html/profilab-expert.html (http://www.abacom-online.de/uk/html/profilab-expert.html).

That looks pretty nice. Unfortunately Korad is not one of the supported devices listed on their website. Reading between the lines, the software uses some sort of driver for each device. Does it include the capability of writing a custom driver for an unknown device? Can it send data alone to the serial port without a CR or LF?

Also unfortunately: that software costs about as much as the Korad. Mind you, it appears to have Spice-like capabilities as well?

Ok, regarding the bugs, it is possible to replace the MCUs with something else with our own program? I bet these funny chips with "Korad" marking are nothing else as ATmega or MCS-51, so it shouldn't be hard to find a pin-compatible replacement.

Two are marked Korad1 and one is marked Korad4. Possibly identical HW with different firmwares. They seem to be associated with the individual channels by location and there are also a j-tag looking header near each. Beyond that, I couldn't say what the heck they might be. I think Korad is trying to protect itself from competitors reverse-engineering and copying the product. Quite possibly they programmed in something to make ID more difficult too.

The one remaining bug in the firmware (showing current limit of 0 in Serial mode) is livable. The remaining bugs are in the PC software for running a script, not in the PSU itself. So for me personally, it's not worth the effort of trying to ID and reprogram the chips.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: Gall on October 20, 2015, 06:01:07 pm
I'd like to reprogram just to make the interface more usable. I personally don't like the way the voltage is set by individual digits.

Also, is it true that the display shows the preset voltage/current, not the actual one?

I don't want to reflash the firmware, I want to replace the whole MCU chip. Anything that is pin-compatible would fit, and there are not so many possibilities. Could you please identify the power, XTAL and SPI (to the DAC) pins?

I'm I right that the controller board is not the same as display board? That is, could one replace the whole board leaving the original display and controls in place?
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: Messtechniker on October 20, 2015, 06:39:22 pm
Does it include the capability of writing a custom driver for an unknown device? Can it send data alone to the serial port without a CR or LF?

As to custom drivers one would have to write a dll. Something which is beyond my capabilities.
But as long as the target unit is responsive through its serial interface then you have many options with "Profilab Expert".
Provided the protocol is known resp. given in the manual. As to doing without CR and LF: I would simply have to find out.

Yours Messtechniker
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: torch on October 20, 2015, 07:19:53 pm
I'd like to reprogram just to make the interface more usable. I personally don't like the way the voltage is set by individual digits.

I'm not sure you understand that part correctly. The granularity is variable by digit, however, it increments/decrements the next leftmost digit after 9. So you can twirl the knob from 0v to 31 volts by single volts, tenths of a volt or hundredths of a volt depending on what you need to do. Or you can go from 0 to 30 volts in 3 steps if you set the tens digit to flashing.

That said, it won't let you go past 31 volts, so if you started at 1.01v and adjusted by tens of volts, the maximum would be 21.01v. You would have to use a different granularity to go higher. If you then switched to single volts, you could go up to 30.01 volts. From there you could switch to tenths and go up to 30.91v.

I can do a little video if the above is still confusing.

For what I'm doing, I don't generally need to adjust hundredths of a volt. I just leave the hundredths digit at 0 and set the granularity at tenths (the granularity remains set unless changed). Changing the voltage is a matter of tapping the channel button once and twirling the volts dial. Similarly, tap the channel button twice and twirl the current dial.

Quote
Also, is it true that the display shows the preset voltage/current, not the actual one?
Only true until the output is turned On. Once the output is turned on, the display changes from showing the presets to showing the actual output (EXCEPT in serial mode, when the display shows 00.00 when outputs are Off and not being actively adjusted -- that's the minor bug I mentioned earlier.)

Quote
I don't want to reflash the firmware, I want to replace the whole MCU chip. Anything that is pin-compatible would fit, and there are not so many possibilities. Could you please identify the power, XTAL and SPI (to the DAC) pins?

Speak slowly and use small words! I will attempt to follow directions, but I'm an old dog trying to learn new tricks. My last quarter century was spent riding a firetruck, not sitting at an EE bench: "Me strong like bull. And smart -- Like freight train."

Quote
I'm I right that the controller board is not the same as display board? That is, could one replace the whole board leaving the original display and controls in place?

Yes, that is correct. There is a 20(?) pin header between the boards as well as a ribbon cable. The outputs are on the control board and the display/knob board sits above those in front of the control board.
[/quote]
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: Gall on October 20, 2015, 08:12:34 pm
I'm not sure you understand that part correctly. The granularity is variable by digit, however, it increments/decrements the next leftmost digit after 9. So you can twirl the knob from 0v to 31 volts by single volts, tenths of a volt or hundredths of a volt depending on what you need to do. Or you can go from 0 to 30 volts in 3 steps if you set the tens digit to flashing.
Yes, that's exactly how I understood that. I think the smaller KD3005P has exactly the same control. I'd like to change the granularity by rotating the knob while pressing it.

And I'd like to make it blink faster.

Quote
Quote
I'm I right that the controller board is not the same as display board? That is, could one replace the whole board leaving the original display and controls in place?

Yes, that is correct. There is a 20(?) pin header between the boards as well as a ribbon cable. The outputs are on the control board and the display/knob board sits above those in front of the control board.
Fine! Thank you! In the worst case I'll just replace the whole board.

I wonder if this ribbon cable should have been shielded...

Title: Re: Inside the new Korad KA3305P linear PSU
Post by: torch on October 20, 2015, 11:43:32 pm
I'd like to change the granularity by rotating the knob while pressing it.

Well you do press and release the knob to change the granularity. Each press moves the granularity one digit to the right. However, if you press and hold the knob then you lock/unlock the keyboard (volts) or turn the beep on/off (amps).

Quote
I'm I right that the controller board is not the same as display board? That is, could one replace the whole board leaving the original display and controls in place?

Quote
I wonder if this ribbon cable should have been shielded...

Why? I'm not saying you are wrong, I just don't understand what makes you suspect that. I don't think there is a lot of HF radiation from either board, it's a linear supply and the regulation seems to be at the other end of the PSU.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: crispy_tofu on October 21, 2015, 02:24:24 am
Just saw this teardown, looks nicely laid out. Thanks for satisfying my teardown urges!  :-/O
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: Gall on October 21, 2015, 02:22:33 pm
Why? I'm not saying you are wrong, I just don't understand what makes you suspect that. I don't think there is a lot of HF radiation from either board, it's a linear supply and the regulation seems to be at the other end of the PSU.
I just suspect that this may be sensitive to the EMI from i.e. the device under test. My old Mastech power supply used to show negative (!) current values in the presence of a small 100 MHz oscillator nearby. No, it was not connected to the oscillator...
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: SantaClaw on December 02, 2015, 05:00:42 am
I think I'll order myself one of these.. comes to 355$ incl shipping & tax though.....
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: torch on December 02, 2015, 05:50:31 am
What part of the world are you in?

Hmmm. Doing the math, you could be in Canada and talking CDN$, since the loony has sunk so low recently.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: SantaClaw on December 02, 2015, 11:27:34 am
Norway, The very north of it too, 69.7269° N, 30.0456° E :D
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: pascal_sweden on December 02, 2015, 11:50:41 am
I was looking at the Korad website, and they seem to have many different versions.

http://koradtechnology.com/en/Products.html (http://koradtechnology.com/en/Products.html)

What is the difference between the KD series (Encoder-controlled and Digital Control DC Power Supply) and the KA series (Digital Control DC Power Supply)?

I am not refering to the D extension (non-programmable) and the P extension (programmable),
but really to the first two characters in the model names: KD or KA.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: SantaClaw on December 02, 2015, 11:53:32 am
http://www.ebay.com/itm/KORAD-KA3005P-Programmable-Precision-Variable-Adjustable-30V-5A-DC-Linear-Po-/111455671404?hash=item19f346946c (http://www.ebay.com/itm/KORAD-KA3005P-Programmable-Precision-Variable-Adjustable-30V-5A-DC-Linear-Po-/111455671404?hash=item19f346946c)

http://www.ebay.com/itm/KORAD-KD3005P-Programmable-Precision-Variable-Adjustable-30V-5A-DC-Linear-Po-/131367286456?hash=item1e9619b6b8 (http://www.ebay.com/itm/KORAD-KD3005P-Programmable-Precision-Variable-Adjustable-30V-5A-DC-Linear-Po-/131367286456?hash=item1e9619b6b8)

Easier to compare ^^

Looks like it's missing the memory features, and it's got a completely different interface just two encoder wheels in stead of encoder wheel + buttons. Otherwise the specs look identical.

The KA series looks to be a bit more expensive.


User manual: http://www.sra-shops.com/docs/srasolder/instructions/ka3305_user_manual.pdf (http://www.sra-shops.com/docs/srasolder/instructions/ka3305_user_manual.pdf)


I assume it handles 240v ? it says 220/230v, but that's usually +-10% right?

Ok, SRA-Shops comfirmed it. It works fine on 240v 50hz :)
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: icpart on December 03, 2015, 09:30:16 pm
Very interesting power supply,
Seems is there also new modification of that PSU with remote sense option. You can see here on picture from Korad website:
(http://koradtechnology.com/images/26.jpg)
Also from description:
Code: [Select]
The remote measurement terminal compensates the voltage drop of the wire Just look of these interesting new added screw terminals on back. 
Also there is modification of that PSU without binding posts maybe from Reichelt Germany :-//:
(http://cdn-reichelt.de/bilder/web/xxl_ws/D400/KD3305_01.png)
Also there is rebranded version under TENMA from Farnell under model number 72-2645:
http://uk.farnell.com/tenma/72-2645/power-supply-bench-0-30v-5v/dp/2478801 (http://uk.farnell.com/tenma/72-2645/power-supply-bench-0-30v-5v/dp/2478801)
But on Farnell website I can't see any screw terminals on back for remote sensing from pictures. But from description in datasheet of 72-645:
Code: [Select]
Complete digital control / programmable
• 10mV / 1mA resolution
• Low noise and ripple
• CV / CC constant voltage and constant current modes
• 5 sets of parameters can be stored and recalled
• 100 sets of stored parameters inside for programmable recall
• The remote measurement terminal compensates the voltage drop of the wire
• Industrial grade, with load for a long time
• Interfaces USB and RS232

Also i tried to find any user manual of that new models but without success.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: torch on December 03, 2015, 11:30:13 pm
I think I read somewhere that those recessed terminals are a European safety requirement. So you can't fry yourself if you accidentally come in contact with 30VDC. Perhaps the screw terminals on the rear are duplicates of the front panel outputs to make up for the lack of screw posts on the front?
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: robert_ on December 04, 2015, 12:01:10 am
I think I read somewhere that those recessed terminals are a European safety requirement. So you can't fry yourself if you accidentally come in contact with 30VDC. Perhaps the screw terminals on the rear are duplicates of the front panel outputs to make up for the lack of screw posts on the front?
Its mostly to keep people from removing the shrouds from their test leads to fit the old-style connectors, and afterwards, have unsafe test leads. From practical experience, that happens all too often.
Actually i fit the safety terminals on everything i build, as i do lots of "high"voltage stuff and therefore, use insulated 4mm test leads almost exclusively. I dont remember having ever neded to directly connect bare wires to any piece of equipment (i DO understand the need to do so for highest precision measurements).
There are these extremely useful little things, quick connect 4mm plugs. Much easier to use, safe and easy to connect/disconnect...
(https://www.buerklin.com/images/dvnrbilder/gross/KapF/F073450.jpg)
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: Electro Fan on December 04, 2015, 12:22:59 am
A little bit off topic but it would be interesting to compare this vs. the Rigol PS. 

I have had a Korad single channel PS for a couple years or so and I think it is a very good power supply.  I'm a Korad fan (and a SRA Soldering fan - where I got the Korad) but for this price range it seems the two offer pretty different designs for a similar price. 

The newer Siglents look like a modern hybrid between the Korad and the Rigol; the Siglents might also be worthy of consideration.

For what it's worth I find the User Interface on the KA3005P to be very straight forward friendly with no muss or fuss - and it appears the KA3305P is pretty similar - which is a good thing.  On the other hand, all the bells and whistles on the Rigol are pretty interesting and when you clean up the "Hello Kitty" UI and put it into the Siglent UI the Siglent looks pretty good.  So for UI, the Siglent is pretty appealing (and the Rigol might be A-OK too - lots of happy users around here), and the Korad is sort of conventional but highly useable.... so it might come down to UI preference, and how well they each perform (in terms of accuracy, stability, etc).
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: SantaClaw on December 07, 2015, 05:49:12 pm
And now, I've ordered one :)
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: TopLoser on December 07, 2015, 06:11:45 pm
And now, I've ordered one :)

Insides look very similar to what's in these:

http://uk.farnell.com/tenma/72-10505/power-supply-3ch-30v-3a-adjustable/dp/2251949 (http://uk.farnell.com/tenma/72-10505/power-supply-3ch-30v-3a-adjustable/dp/2251949)

They just merged the two identical sets of boards in the Tenma unit into 2 larger boards and put a new front panel on it.

I'm selling the above Tenma supplies for £50 plus £20 European shipping, they don't have the RS232/USB interface though.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: SantaClaw on December 07, 2015, 07:16:51 pm
That thing is only 3a
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: TopLoser on December 07, 2015, 07:24:08 pm
That thing is only 3a

'That thing', I like that description of them!
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: pascal_sweden on December 07, 2015, 07:28:38 pm
Is it better than or similar to the Siglent SPD3303X power supply?
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: dom0 on December 07, 2015, 07:54:40 pm
I think I read somewhere that those recessed terminals are a European safety requirement. So you can't fry yourself if you accidentally come in contact with 30VDC. Perhaps the screw terminals on the rear are duplicates of the front panel outputs to make up for the lack of screw posts on the front?

No and no. Most likely the rear screw strip is for the added sense lines, since I can't see anything like sense contacts on the front panel.

The product image above looks shopped anyway. The angle of the shrouds inside the 4 mm sockets doesn't match the angle of the front panel.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: SantaClaw on December 08, 2015, 06:03:51 pm
Insides look very similar to what's in these:


http://uk.farnell.com/tenma/72-10505/power-supply-3ch-30v-3a-adjustable/dp/2251949 (http://uk.farnell.com/tenma/72-10505/power-supply-3ch-30v-3a-adjustable/dp/2251949)

Control board looks nothing like it:

Korad:

(http://picturehosting.verhey.org/korad/09-control_board.JPG)

vs

Tenma:

(http://seriouslyembedded.com/wp-content/uploads/2015/04/P1010014.jpg)

vs

Korad:

(http://picturehosting.verhey.org/korad/02-inside_right.JPG)

The Tenma looks to be an older design, as it's very similar to what was tested here (2012):

EEVblog #314 - Korad KA3005P PSU Teardown (https://www.youtube.com/watch?v=g94mpom2Ahs)

Otherwise it's not programmable, only 3a per channel, for a total of 6a max in series, I need at least 5a per channel for my usage. Thanx for the offer, but no thanx, it's not what I'm after.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: torch on December 08, 2015, 07:00:37 pm
'That thing', I like that description of them!

So give us a better one. 

I can appreciate that you might not have enough margin at that price to send one "down under" to a man who makes room on his bench by throwing $10,000 scopes to the floor, but as a vendor, you must have one around that you could open up and demonstrate to us. You know what we want: pros, cons, specs, real world tests and lots of pictures.

Who knows? Maybe you'll attract the interest of someone who wants a bench supply but doesn't need 5 amps per channel or a programmable interface.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: TopLoser on December 08, 2015, 07:31:14 pm
'That thing', I like that description of them!

So give us a better one. 

I can appreciate that you might not have enough margin at that price to send one "down under" to a man who makes room on his bench by throwing $10,000 scopes to the floor, but as a vendor, you must have one around that you could open up and demonstrate to us. You know what we want: pros, cons, specs, real world tests and lots of pictures.

Who knows? Maybe you'll attract the interest of someone who wants a bench supply but doesn't need 5 amps per channel or a programmable interface.

See the teardown above, that's exactly what the Tenma ones are. The dual channel ones are just two identical sets of boards in one case.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: SantaClaw on December 09, 2015, 07:09:08 am
I wonder if I get the "new" version with the EU style banana terminals on the front... I did ask the seller if it came with the updated firmware for the M4 memory button issue, and they replied that all their stock had this update.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: SantaClaw on December 09, 2015, 07:10:56 am
See the teardown above, that's exactly what the Tenma ones are. The dual channel ones are just two identical sets of boards in one case.

1 question though, I see that the Tenma does NOT come with a 110v/220v selector switch, what is it's voltage range ?
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: TopLoser on December 09, 2015, 07:22:27 am
See the teardown above, that's exactly what the Tenma ones are. The dual channel ones are just two identical sets of boards in one case.

1 question though, I see that the Tenma does NOT come with a 110v/220v selector switch, what is it's voltage range ?

Google says 207v-253v
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: torch on December 09, 2015, 08:06:08 am
Is it better than or similar to the Siglent SPD3303X power supply?

Based on recent Siglent business practices, I'd say anything is better than theirs.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: SantaClaw on December 17, 2015, 03:47:23 pm
Well, It arrived today! Considering the shipping costs, I suppose I shouldn't really be surprised. Looks identical with the one torch got.
Fired it up, not forgetting to  swap over the 220/110V switch, it seems to be working just fine.
Came with TWO sets of banana/alligator leads, extremely slippery silicone/plastic protector on the alligator clips.

So, how do I feel it works? Well, it's down to what I have to measure it with.
lol, I've got a Uni-T (yeah, you can all stop laughing now.) UT81C scope meter, the top of the range scope meter from Uni-T.

According to it, (yes, I AM going to buy me a fluke 87, stop bugging me about the Uni-T)  it's as following:

Indicated: 5.00V on the psu, measured: 4.99-5.00V
Indicated: 31.00V on the psu, measured: 31.03V

Indicated: 0.01v on the psu, measured: 12.4mV(without REL 400mV range)  [0.012V 4V range]
Indicated: 0.01v on the psu, measured: 71.9mV [with REL 400mV range] [0.072V 4V range]

^So, that's why I don't really trust it all that much, and it IS a Uni-T lol^

How bout current?

Well, I hooked up an 56ohm (5%) resistor, because I had one.. lol

4V 0.5A current limit: Blew 500mA fuse on multi-meter... lol

Tried again: 4V 0.5A current limit, this time, on the A range on the multi-meter... lol
Indicated 4V, 0.066A on the psu, measured 0.071A on the meter 4A range.

5V 0.5A current limit:
Indicated 5V 0.084A Measured 0.089A 4a range.

Resistor is heating up :)

5.5V 0.5a current limit:
Indicated 5.50V 0.092A Measured 0.098A 4a range.

6V 0.5A current limit:
Indicated 6V 0.102A Measured 0.107A

Btw, Meter is indicating 0.000A when psu output is off.

I also shorted it out @ 31V 5.1A, and 0.001V 5.1A both channels no problems at all, fan spun up loud.

The only issue I have met, is that one time I powered it on, it turned on with the output on !!
I think it was because of the settings in the software? I've been unable to replicate it.

I set all the M buttons to 0.00V and 0.00A to be on the safe side. In case I hit one accidentally.. lol

So, the USB interface is working fine. Below is both the PSU interface(on the right) and the Meter interface (on the left)
As you can see, it's indicating 6V 0.102A on the psu, and 0.107A on the meter.

(http://i5.photobucket.com/albums/y199/santaclaw/afe95000cf43c0753e0cafdaf8b98e3b_zpscn32pft2.gif) (http://s5.photobucket.com/user/santaclaw/media/afe95000cf43c0753e0cafdaf8b98e3b_zpscn32pft2.gif.html)

Note, update rate on the PSU is much higher then the gif will allow, similarly the update rate on the meter is set to 1sec, but you can get "instant" updating by disabling it.
Alos, the most noisy thing is the regulators for the fan, they keep buzzing, changing with the pitch of the fan...
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: SantaClaw on December 17, 2015, 07:18:55 pm
Info: The way you set Over Current and Over Voltage protection is very easy.

I found it by looking at the screen, and noticing that there was a "SET" light besides the indicator lights for OVP and OCP.

Basically, if you push and hold the OVP or OCP buttons, first one then the other, or separately ofc, both channels will display the currently set OVP and OCP values, as long as SET is glowing next to OCP or OVP, you can set it just like you set the voltage and current during normal operation.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: torch on December 18, 2015, 01:50:50 am

The only issue I have met, is that one time I powered it on, it turned on with the output on !!
I think it was because of the settings in the software? I've been unable to replicate it.


Mine powers up in the "on" state if it was powered down in the "on" state and vise-versa.

Quote
Alos, the most noisy thing is the regulators for the fan, they keep buzzing, changing with the pitch of the fan...

Mine don't buzz. Maybe yours has a bit of a gap between a heat sink and the board?

I'm curious, does yours have the serial mode bug that mine exhibits with my replacement board? IE: When Serial mode is selected with the output turned off, the current limit is displayed as 0.000 on both channels. (although it works properly and displays properly when setting the current).
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: SantaClaw on December 18, 2015, 06:49:52 am
I'm curious, does yours have the serial mode bug that mine exhibits with my replacement board? IE: When Serial mode is selected with the output turned off, the current limit is displayed as 0.000 on both channels. (although it works properly and displays properly when setting the current).

Yup, It does the same thing. Ofc, I set the current limit on CH2 and it changes on both channels.

Also, the most noisy thing is the regulators for the fan, they keep buzzing, changing with the pitch of the fan...

Mine don't buzz. Maybe yours has a bit of a gap between a heat sink and the board?

Well, they/it will start making a buzzing/grinding sound about 45 to 60 seconds after I turn it on, with no load.
I had the cover off, and it looks like it applies very low power to the fan at this stage, PWM? it doesn't spin on it's own, but starts if I give it a little help. The fan spins easily though, so it's working as it should, also it starts on it's own if I leave it alone long enough.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: torch on December 18, 2015, 12:58:02 pm
Yup, It does the same thing. Ofc, I set the current limit on CH2 and it changes on both channels.

Yes, Ch2 is the master.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: SantaClaw on December 18, 2015, 01:31:41 pm
Yes, Ch2 is the master.

Yup, both in Parallel and Series :)
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: SantaClaw on December 19, 2015, 02:29:59 am
Nice feature though:

If you are using the USB interface and you turn off the program, or disconnect the USB with the output ON, the buttons will automatically LOCK, as if you push and hold the CH1 coder wheel (hold it down to unlock the buttons).

Not that nice feature though:

When opening the USB interface program, If the PSU output is on with a set current and voltage, well basically it don't matter,  the meter will turn the outputs OFF, and it will automatically set current/voltage /ocp/ovp to what ever the program is set to on default, in my case, it jumped from 5V/500mA to 31V/5.1A on both channels, disaster if I had just hit the output on button.  SO, be really freaking careful !!
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: torch on December 19, 2015, 02:55:43 am
I have been swamped and not had time to play further with the software, but IIRC, that behaviour is in the software, not the firmware. I think the software is sending the "lock" command and other settings when it first boots up.

When time permits, I'm going to take a stab at creating better software for it. Particularly the program scripting. I have figured out the protocols, so it's a start...
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: SantaClaw on December 19, 2015, 03:57:06 pm
Sounds great, btw,with both channels set to 5v, no load I measured 5.00v on ch1 and ch2, but I "only" get 4.98v on ch3 in the 40v range. I just ordered myself a new siglent SDM3055 bench meter, Hopefully IT will be a little more "trustable" than my uni-T :D
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: Kkkkkk on January 24, 2016, 10:49:38 am
Stupid question :
When I use the KOARD 3305 in series operation can I fire it up to 60 volts
and in parallel up to 10 amps?

Thx
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: SantaClaw on January 24, 2016, 10:58:58 am
I believe it's, 31v 10A in parallel or 62v 5A in series max output.. Yup, confirmed, only got 3a when set to 3a on CH2 and CH1 in series.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: torch on January 24, 2016, 04:40:14 pm
Yes, it can supply either a maximum of 5A (5.1A actually, IIRC) at 62v when connected in series OR a maximum of 10A (10.2A) at 31v when connected in parallel.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: Kleinstein on January 24, 2016, 05:41:13 pm
You may not get the maximum voltage and maximum current from both channels at the same time, especially if the line voltage is at the low end. These cheap supplies are usually don't have filter caps that have much reserve to compensate for lower line voltage - adding more capacitance could also overload the transformer, so this is not a good idea. So just don't count of the full 5 A at 30 V, depending on the tolerances and line voltage it might be only 4 A at 30 V or 28 V at 5 A before ripple comes through. 
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: SantaClaw on January 24, 2016, 06:32:48 pm
It had no problem providing 10A dead short when in paralell
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: Kkkkkk on January 24, 2016, 06:40:56 pm
Thx for the quick response.
That's what I was asking for. Possible max voltage OR max current.
The technical data sheet and the manuals from KOARD are really crappie  :bullshit:
I know running equipment on its upper limit is always gambling and you
pray that Chinese work with safety margins, too.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: torch on January 24, 2016, 07:09:24 pm
It had no problem providing 10A dead short when in paralell

Yes, but the voltage drops off to next-to-nothing with a dead short because the unit goes into constant current mode.

I think Keinstein is making reference to possible voltage sag, wherein the voltage drops off before the unit starts limiting the current because the transformer just can't deliver the wattage. Especially likely if the line voltage going into the transformer is low.

I did some testing when I bought this, first with a carbon pile (which did not have a fine enough adjustment for precision) then stringing together 100w (120v) light bulbs in parallel to provide a load. I forget the exact numbers, but I snuck up on 5 amps @ 60v by adding more and more bulbs until I was just shy with no voltage sag. Adding one more bulb triggered the CC mode, which throttles the voltage to limit the current. I neglected to draw anything from Channel 3 during the test, but the Korad can at least deliver full power through 2 of the 3 channels simultaneously.

FWIW, when I asked the vendor, he replied the weak link would be failure of the cooling fan on the internal heatsink, but as long as the fan keeps going it can supply full power indefinitely.

But then, taking a vendor's word could be like buying a used car from the guy who swears it was only driven by a little old lady to church on Sundays...  :-\

Title: Re: Inside the new Korad KA3305P linear PSU
Post by: Gall on February 29, 2016, 08:43:10 am
Hi,
I wonder how the series mode work. I'd like to use it for an opamp dual supply. Does it work just as two independent power supplies of the same voltage connected in series, or do their voltages follow each other in case of overloading (going to the CC mode) just one of them?
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: torch on February 29, 2016, 12:38:24 pm
I did not know, nor had I thought to check. So I just did a quick experiment.

Series mode, 3vdc per channel, (6vdc total ch.1+ to ch.2 -), current limit to 1.1 amp per channel,

metering  ch. 1 + to ch. 1 -,
shorting ch. 2 + to ch. 2 - :
ch. 1 continues to supply 3vdc, ch. 2 switches to CC mode @1.1A

metering ch. 2 + to ch.2 -,
shorting ch. 1 + to ch. 1 - :
ch. 2 continues to supply 3vdc, ch. 1 switches to CC mode @1.1A

metering ch. 1 + to ch.2 -,
shorting ch. 1 + to ch. 2 - :
both channels drop to 0vdc, both channels switch to CC mode @1.1A each

So I would say it behaves like 2 independent supplies in the case of overload.

(as noted earlier, in both series and parallel modes, ch.2 is the master. ie: the set points of ch.1 are changed to mirror the existing set points of ch.2 when entering either mode. changing ch.2 set points changes ch.1, and ch.1 controls are no longer available)

Hi,
I wonder how the series mode work. I'd like to use it for an opamp dual supply. Does it work just as two independent power supplies of the same voltage connected in series, or do their voltages follow each other in case of overloading (going to the CC mode) just one of them?
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: Gall on February 29, 2016, 04:48:47 pm
Thank you. That means, a dual-supply circuit will become an asymmetric power in case of overload. I wonder how hard it would be to fix that...
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: Aeternam on March 06, 2016, 02:01:47 pm
I have one of these and I've been very happy with it.

I've recently hooked it to my scope to see how it was behaving, and I've noticed some strange ripples when I turn it off when the output is set to OFF (see attachments). Is this something I should be worried about? I'd hate to have to disconnect the leads when I turn it off to go watch some telly...

Also, it makes a quite audible GONG sound when I turn it on. (Not always though.) Is this designed so that you're awake when you start using it?  ;D
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: mos6502 on March 18, 2016, 12:28:24 am
I have one of these and I've been very happy with it.

I've recently hooked it to my scope to see how it was behaving, and I've noticed some strange ripples when I turn it off when the output is set to OFF (see attachments). Is this something I should be worried about? I'd hate to have to disconnect the leads when I turn it off to go watch some telly...

Also, it makes a quite audible GONG sound when I turn it on. (Not always though.) Is this designed so that you're awake when you start using it?  ;D

When the output is off, it's high impedance. You're just picking up random noise with your scope. To test this, just hook up a 1k resistor at the output.

As for the *boink* sound: say when you turn the supply off, the switch opens exactly at the top of the positive half wave. The transformer core will remain magnetized in that direction. Then when you turn it on again, you might turn it on at the top of the negative half wave. The winding will create a magnetic field that is opposite to the already existing field of the core. So you get an instantaneous mechanical force of the winding pushing against the core. It's kinda like the transformer is being hit with a hammer.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: YottaByte on June 04, 2016, 04:40:49 pm
I just received a "refurbished" KA3305D from SRA. Their tech said that any returns for whatever reason are thoroughly tested before being resold, so of course I expected everything to work. But unfortunately that wasn't the case. On Ch3's 5V fixed terminal I only get a few mv output. Any suggestions before I call their tech support Monday? Thanks.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: SantaClaw on June 04, 2016, 04:46:41 pm
I just received a "refurbished" KA3305D from SRA. Their tech said that any returns for whatever reason are thoroughly tested before being resold, so of course I expected everything to work. But unfortunately that wasn't the case. On Ch3's 5V fixed terminal I only get a few mv output. Any suggestions before I call their tech support Monday? Thanks.

It may be a stupid suggestion, but are you measuring between the + and - and not the - and the GND?

:D
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: YottaByte on June 04, 2016, 04:57:27 pm
SantaClaw,
Thanks for the quick response! No such thing as a stupid question. The mv output is between the + and - terminals. I haven't opened the case to check inside. Just disappointed, especially after talking to the tech who confirmed that refurbished units were thoroughly tested. BTW, the PS looks brand new, only the user's manual was photocopied.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: SantaClaw on June 04, 2016, 05:01:18 pm
Yeah, well, then I'm out of suggestions, I just measured mine, it's pinned at 4.98v, if I set the two other channels to 5.00v they measure at 4.99v, but that could be my meter as well...

Title: Re: Inside the new Korad KA3305P linear PSU
Post by: YottaByte on June 04, 2016, 05:37:27 pm
Thanks, I'll just have to wait until Monday to call them.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: YottaByte on June 06, 2016, 04:22:32 pm
Opened it up and after finding no obvious loose connections, I re-seated every internal plug, which fixed the problem. Great PS at an even greater price!
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: SantaClaw on June 06, 2016, 04:23:31 pm
Excellent news, yeah, it's a good psu for the money :)
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: YottaByte on June 06, 2016, 09:10:44 pm
FWIW, I got this Korad KA3305D for $139 delivered from SRA Solder. Although they are sold as refurbished units, the one I got looked brand new and was shipped in the factory Korad box. The only difference being that the manual was a black and white printout of the factory manual. Hard to get anything close to this for that price, especially since I didn't need the Programmable model. So far I am extremely pleased with this unit.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: bitwelder on June 07, 2016, 05:41:29 am
Gotta ask: is it possible to find anywhere the USB module used in the Korads, or are the schematics available?
I have a rebranded version of the Korad dual PSU that doesn't have the USB interface (but has the metalwork done to host it), so if possible it would be nice to 'mod' it.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: schuc on June 28, 2016, 11:41:30 pm
GREAT info and thank you so much for this thread.

I am just getting into electronics and am trying to get a few necessary tools without breaking the bank as I am new and this will be at a hobby level.  I just got a Bryman multimeter and am looking at this power supply.  It was fun reading the past 6 pages of dialog on this and helps give me a feeling for what you have been experiencing.  It seems like a winner at this price range to me.

I'm interested in doing some Arduino and Raspberry Pi projects for various purposes(mostly sensor monitoring and graphing of collected data currently, etc).  I have a LOT to learn and need to get the basics down but it's going to be a fun ride.

Anyway, thank you for all the info related to this PSU.   :-+
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: Scottjd on November 08, 2016, 07:01:56 am
I decided to do a review on this unit. I know some bugs have been mentioned, this one I tested and reviewed is the latest with none of the bugs mentioned in this thread.
I also wanted to post the review since I know some people asked about a video.

TORCH: I hope you don't mind, I also put this thread in the description of my video for people that want to see detailed photos of the internals since you have posted such nice photos.

https://youtu.be/WRZY9mYmFBk
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: rsfoto on November 09, 2017, 11:05:41 pm
Hi,

As I was in search of a PSU too and having read a lot I decided based on many of the opinions here to get a KORAD KA3305P power supply.

I got it yesterday and started to learn it.

OK with the unit there was a CD, a USB cable as well as 2 (two) yes 2(two) power cables with banana and crocodile clamps, but, yed but ... after seeing the images of the burnt PSU

https://www.youtube.com/watch?v=B6IhEz0Gzyo (https://www.youtube.com/watch?v=B6IhEz0Gzyo)

and having seen in You tube the tear down of a similar unit by bigclivedotcom in which he analyzed the possible why of the fire

https://www.youtube.com/watch?v=70d6LBXw3o0&t=49s (https://www.youtube.com/watch?v=70d6LBXw3o0&t=49s)

the first thing I did with the cables weas to inspect how the ends where mounted and ... SURPRISE ...

The same way as in bigclivedotcom video.

Well I am going to make a good connection by tinning the screwable end and soldering the cable to the crocodile.

I would like to thank all of you for those good messages which help a lot for taking decisions.

Attached some images of how I got the cables.

best regards Rainer
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: Scottjd on November 10, 2017, 05:20:54 am
Congrats on the new power supply. It’s not the burnt one, right? JK
I don’t remember if I mentioned this in the newer triple, but I know I do mention it in the first kora triple older one I reviewed to just ditch the cables. I think the other one I didn’t even mention them bakes it came with? But I dint really remember.
Depending on the power supply you have, you want the cables to be good quality with low resistance. You can even get nice ones without spending to much from Frankie over at 99centHobbies
http://stores.ebay.com/99centhobbies (http://stores.ebay.com/99centhobbies)

Title: Re: Inside the new Korad KA3305P linear PSU
Post by: rsfoto on November 10, 2017, 01:59:53 pm
Congrats on the new power supply. It’s not the burnt one, right? JK
I don’t remember if I mentioned this in the newer triple, but I know I do mention it in the first kora triple older one I reviewed to just ditch the cables. I think the other one I didn’t even mention them bakes it came with? But I dint really remember.
Depending on the power supply you have, you want the cables to be good quality with low resistance. You can even get nice ones without spending to much from Frankie over at 99centHobbies
http://stores.ebay.com/99centhobbies (http://stores.ebay.com/99centhobbies)

Hi Scott,

I got the KA3305P. Your review video was one of the main reasons I bought this brand.

Well as having read it comes with no cables I ordered some cables specifically the Brand Elenco and Type TL-16. Having seen the images on Amazon I thought they were good and OH what a deception. They are even stiffer then the ones supplied with the KORAD PSU. On the other side I also ordered some other cables from Elenco specifically the BNC cable type TL-3 as well as the TL-12 and surprisingly they are better then their own TL-16. The pair of Elenco TL-16 cost about US $ 8.00

I live in Mexico and it is even nowadays not so easy to find good stuff here. Unfortunately Mexican consumer wants everything cheap and the sellers adapt to it and if I shop in stores with good quality the stuff costs nearly double or triple the price somewhere else like in Europe or USA.

Already happened with a Arduino shield for a NANO. I plugged it into the power supply and PENG my NANO fried. Before that I had already contacted the Mexican seller to tell him that some soldered parts were all croocked on the PCB and his answer was ... Well you know you bought chinese and that is the quality I can sell. I ussed to sell better stuff but nobody bought it ... As you can see they do not know how to sell and go the easy way ...

So far at the moment my current requirements are not big so the cables more or less do work for me. Mainly Arduino projects but I was tired not being able to play with voltages and learn more about electronics.

Will keep searching for cables

What I found out is that if I have channel 1 voltage at 0.00 I can nor adjust channel 2 in any way. Getting the adjustment up to 0.01V in CH1 then I can adjust CH2 :-) I know it is nonsense not to have something adjusted but it happened by pure curiosity that I found it out. Same happens with the current adjustment. 

regards Rainer
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: kelchm on January 16, 2018, 06:04:02 pm
Can anyone share the dimensions of the KA3305P? It looks like the dimensions listed by SRA are incorrect.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: Scottjd on January 17, 2018, 06:02:43 pm
Can anyone share the dimensions of the KA3305P? It looks like the dimensions listed by SRA are incorrect.
Measurement are just a tad bigger rounded off the actural size.
They include the feet, knobs, screw heads, handle on top, and front posts.
In my video, o don’t think I measured or considered the feet, or the handle on top.

Mine is a KA3305P, I don’t think the extra programming USB plug port makes a difference in this size. They all go into the same case, just an added whole for the USB and additional PCB board plugged into the unit inside the case.
Don’t forget to consider how far the plug sticks out the back when it’s plugged in, you can always buy a right angle plug also so it doesn’t stick out as far off a shelve.

I’m thinking this is what your looking for to make sure it will fit in the space you want it?
Scott
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: Scottjd on January 17, 2018, 06:36:31 pm

What I found out is that if I have channel 1 voltage at 0.00 I can nor adjust channel 2 in any way. Getting the adjustment up to 0.01V in CH1 then I can adjust CH2 :-) I know it is nonsense not to have something adjusted but it happened by pure curiosity that I found it out. Same happens with the current adjustment. 

regards Rainer

Thinking back, I believe this is one of the bugs I reported to Korad.
The other gotcha I noticed on older manufactured units, is if you have the power enabled, turn off the unit, then turn it back on it will still have the power enabled.
UPDATE: Its been a while using this one since I own 3 different 3 channel PSU’s. But I just remembered on this newer model it wasn’t a bug. Channel 2 is the master by design. So if channel 2 it turned off all the way it cuts any power going to channel 1. I know this is sort of backwards, I would of rather they made channel 1mthe mater, but they didn’t.

Still I have 2 of these, the one older 3 channel and they are all still running as expected.
Note: I did have a fan go out on my older unit, well it didn’t stop all the way, just made some weird bearing noise sometimes when I turned it on. So I want to mention if you ever replace this fan on the older 3 channel units, it’s a 24V fan, not a 12V fan like a regular common computer fan.

So watch out for this, I thought the bug you mentioned was corrected the same time that the power staying on was corrected. It’s possable you might have bought old stock, or a refurbished old unit they sold to you?

The opinion on the power bug is mixed. Some people like this and consider it a feature because if the main power goes out when taking long time lapsed measurements on a project, then the unit continues to put power out to,the DUT when the mains power is restored. This only works of the logger is battery operated. I don’t know if a mains powered logger would continue taking measurements if the mains went out, this would depend on the logger unit and it features.

I reported this because I considered this a potential danger since the unit is capable of putting out 62VDC and 5 Amps, or 32VDC and 10 Amps, or 32VDC and 5 Amps depending if its running in serial or parallel mode, or how you have it wired at the time.

You might want to test this. Unfortunately it does not have the ability to update firmware, but was fixed and corrected with a firmware. You can contact Korad or your local supplier, sometimes they might be willing to just send a replacement board with the new firmware loaded on the chip. Its cheaper then shipping to them, but only request this, or attempt to replace the board if you feel comfortable wit something like this. It has a lot of capacitors and stored power that can be lethal or give you the shock of your life.
Scott
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: Candid on August 17, 2018, 11:26:10 pm
Also, the most noisy thing is the regulators for the fan, they keep buzzing, changing with the pitch of the fan...

Mine don't buzz. Maybe yours has a bit of a gap between a heat sink and the board?

Well, they/it will start making a buzzing/grinding sound about 45 to 60 seconds after I turn it on, with no load.
I had the cover off, and it looks like it applies very low power to the fan at this stage, PWM? it doesn't spin on it's own, but starts if I give it a little help. The fan spins easily though, so it's working as it should, also it starts on it's own if I leave it alone long enough.
I got one of this PSUs from Welectron who stated to me that the units they sell are form latest 2018 charge. It does not have the M4 bug others I did not check up to now.

What I realized was that I hear a noise from the fan that did make me think that it is defect especially in low power. I checked it with direct voltage and the fan is ok. Then I checked the voltage the fan gets from the psu. Can someone check this with his unit? It is controlled with PWM. My fan runs all the time even without channels on. This "rippel" on the voltage is producing a little annoying sound. When the fan runs faster you can not really hear the ripple but when slow running it is a little disturbing and I wonder how long the fan will run with this special voltage it gets.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: spidola on August 18, 2018, 10:04:34 am
This "rippel" on the voltage is producing a little annoying sound. When the fan runs faster you can not really hear the ripple but when slow running it is a little disturbing and I wonder how long the fan will run with this special voltage it gets.
What if you connect a capacitor in parallel to the fan's power pins?  ;)
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: Candid on August 18, 2018, 03:35:29 pm
That was my first thought and I think I will test it shortly.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: Scottjd on August 19, 2018, 10:49:57 am
I have 2 of these, one has a low power and barely spinning fannthat turns in after it powers up about 1 minute(but output power is off).
The other, the fan stays off until I use the output and have a load on it, as it heats up the fan spins, depending on the temperature regulates how fast the fan spins. The difference between the units could be the locations of the sensor for the temp, or even how much thermal compound is applied?
Or maybe it’s a calibration thing, and at what room temp it was calibrated at?
It could also be some fans start to spin with less current then others, but both units might be putting out the same starting up current and voltage? Or one fan has slightly smother bearing then the other?

Yes, it is some PWN depending on the temp of the unit under load that speeds the fan up. I think the cap might give it that extra lush to keep it in a low spin on the cold start. But this might also depend on how stable the temp of room/house is?

I don’t recall seeing any variable resistor to adjust this for the fan.

I would try this with my units, but they are lacked and ready to move. Also even when I get my new place and the lab unpacked I might not have both of them anymore. I’m working with some local schools to give away some of the extra stuff I don’t need like 3 Korda PSU, and q Rigol DP832. I think I can afford to give up 2 of the Korads and put them to good use with the high schools engineering class or robotics club.
Also less stuff I need to move, or out in storage until I buy a new place.
Scott
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: willumpie82 on October 28, 2018, 10:51:29 am
I just received my Korad KA3305P (unfortunately received a Tenma rebrand with "safety" binding posts instead of screw terminals)
It seems that they still install the factory broken fans, although PWM controlled it makes an annoying rateling noise. Like it should I took it apart before turning it on, All the wiring was nicely tucked and secured but found the mains switch kinda loose (screws not completely fastened) I removed the handle to make it stack better with my other equipment, with it's 10ish kg it is not so portable after all.
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: willumpie82 on November 11, 2018, 12:01:30 pm
I wanted to fix that fan buzzing, but apperantly it is not caused directly by the fan, the PWM control makes the fan hummm. I installed a new-ish fan and the problem retains. When I was at it I also took the effort of cleaning up the heat compound mess it came with.

there are ceramic isolators between the powertrannies and the heatsink, because of the fan retaining method used you have to disassemble the complete heatsink because a big cap is in the way of one of the screws. the fan itself has to be modified to fit in the slot of the heatsink.

below some pitures I took in the process
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: Scottjd on November 11, 2018, 07:35:43 pm
The only way to get the fan to stop under normal powered on and no load would be to use a fan that spends easier, and used less power. It’s the fan trying to spin at the minimum powers being delivered and not enough to get it started. Or maybe if the room was slightly colder with the ambient temperature it could be at a stop. When the fan stutters, if you spin it a little it will probably maintain a slow speed.
I didn’t realize you were going to replace the fan or I would have mentioned that before.

On some of the units you can adjust the output power of the contact on 5V rail in the back left (or right) corner with a variable resistor. You can measure the output from the posts with a load and inline meter, then turn it down a little if you dint use this 5 volt rail. Or maybe turn it down so you can still use it, but instead of it delivering 3 amps you might only get 2 Amps.
By turning this down it doesn’t work as hard or heat up as much with a 5 volt rail that is constantly on and not being used. This should allow the idle temperature to be lower, and as a result the thermal triggered fan PWN will put out less hopefully resulting in the fan not trying to start getting in the stutter.
So if you don’t use the 5 volt rail, this could be an option for you?
Hope this helps,
Scott
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: Pnoxi on March 14, 2019, 06:25:12 pm
Power supply Tenma 72-2630 (Korad KA3303D ?) at a good price! 95.92€ + VAT

https://sk.farnell.com/tenma/72-2630/power-supply-bench-0-30v-5v/dp/2478798 (https://sk.farnell.com/tenma/72-2630/power-supply-bench-0-30v-5v/dp/2478798)
Title: Re: Inside the new Korad KA3305P linear PSU
Post by: SantaClaw on March 14, 2019, 06:44:01 pm
Just want to mention, I've used my KA3305P for nearly 4 years now, It's been flawless for my usage.