Cheap Bench PSU - What to look for?

[radiolistener]

KORAD is pretty popular.
its 109.99 USD on amazon though ... at double the price of what I ordered MATRIX MPS-3206 at 56.99 usd with the only additional feature the KORAD has is a lock function, so not as cheap.

I bought my KORDA KA3005D for about 80 USD from local web-store. There is not only lock feature.

The main and significant difference is digital setup. It means there is no risk that you will get high voltage pulse due to bad mechanical contact on potentiometer. KORAD doesn't have potentiometer, it uses DAC to setup reference for current and voltage. At the same time it use fast analog regulation.

The next significant advantage of KORAD, you can calibrate it and it works pretty well, can be used even as precise voltage source. No analog potentiometers. You're just set required voltage with encoder, press ON and get very precise voltage level. The same for current. You can setup current limit with 1 mA resolution.

The next significant advantage of KORAD is that all possible modes are included: OVP, OCP, CV, CC.

The next significant advantage is that KORAD display works for setup voltage/current regulation when output is disabled and when you enable output it turns into measurement mode, so you will see actual voltage/current. This is very useful for measurement, because there is no need to connect multimeter in order to measure current consumption and actual voltage

Also, memory for 4 settings and LOCK mode.

[Electro Fan]

KORAD is pretty popular.
its 109.99 USD on amazon though ... at double the price of what I ordered MATRIX MPS-3206 at 56.99 usd with the only additional feature the KORAD has is a lock function, so not as cheap.

I bought my KORDA KA3005D for about 80 USD from local web-store. There is not only lock feature.

The main and significant difference is digital setup. It means there is no risk that you will get high voltage pulse due to bad mechanical contact on potentiometer. KORAD doesn't have potentiometer, it uses DAC to setup reference for current and voltage. At the same time it use fast analog regulation.

The next significant advantage of KORAD, you can calibrate it and it works pretty well, can be used even as precise voltage source. No analog potentiometers. You're just set required voltage with encoder, press ON and get very precise voltage level. The same for current. You can setup current limit with 1 mA resolution.

The next significant advantage of KORAD is that all possible modes are included: OVP, OCP, CV, CC.

The next significant advantage is that KORAD display works for setup voltage/current regulation when output is disabled and when you enable output it turns into measurement mode, so you will see actual voltage/current. This is very useful for measurement, because there is no need to connect multimeter in order to measure current consumption and actual voltage

Also, memory for 4 settings and LOCK mode.

+1
... and it’s a linear power supply vs the MPS-3206 switching power supply
 

[innkeeper]

I stand behind what I said in that it has the same operational features as the MATRIX MPS-3206.

all-digital uses encoders and not potentiometers.
same resolution 1mv / 1ma for precise settings.
it has OVP and OCP and is CC ancd CV supply.
and yes the current and voltage display and setting work like your korad, displays current voltage and current, and also allows you to set voltage and current on the display too.
it has 5 memories. (korad also has 5 but only 4 buttons .. weird quirk)

So yes, the only operational difference is it has no lock feature, oh and it has one more memory setting button.

the only REAL difference is that the Korad is not switching based, It is a linear supply "heavy iron" as opposed to the Matrix using a switching supply,
Is that worth double the price .. well maybe. If the switching is leaking switching noise either out the outputs or down the ac line then definitely yes it's worth the extra money for me.
if they were the same price, would I have gotten Korad?  definitely yes.  I am a linear power supply fan.

For the original poster, who is working on mainly playing with STM32, Arduino stuff, he won't notice the difference and might be the perfect cheap solution. I tend to work on a wide range of things including RF and Audio along with digital stuff so for me, it makes a difference.  As I posted, it's not a primary supplies, so I can live with some known sins if there not too bad.

Remember the goal here is CHEAP but still good/usable.  Best bang for the buck.

I'm starting to sound like a matrix MPS-3206 fanboy, but truly I am not, I haven't got this thing in my hands yet.  Just keeping the specs straight. 
I have to see what the deal is with switching noise. That could be a deal-breaker for me. but.. seriously .. bang for the buck wise, if you don't care about it being a switching supply then it's an awesome deal.

Not sure if you have seen any teardowns of it, but it appears like is well built, but that doesn't mean electrically quiet. ... I'll see when I get it.

[Electro Fan]

Back on the Korad, one feature that doesn't get much attention but that was mentioned by radiolistener is the ability to calibrate the power supply.  This can be done externally with the user interface (no need to open the enclosure).  This might not be a widely known feature, and it might not be needed by most users, but it can be pretty useful for dialing in a unit.

But it's good to have choices.  Maybe the MPS-3206 will provide low enough noise and good enough accuracy at it's price point.  It's good to have competition in the market.  Let us know what you find when you get a chance to test it out.

[innkeeper]

Got my 2 Matrix MPS-3206 supplies

quick measurements

Code: [Select]

                           P-P           P-P
              P-P     switch noise   switch noise
 V     I     ripple  (20Mhz limit)  (no B/W Limit)
5v  0.163A   3.1mv      26mv            73mv
5v  1.91A    5.4mv      35mv            86mv
15V 1.97A    6.7mv      42mv           106mv
15v 5.70a   14.0mv      66mv           167mv 

all masurements are peak to peak

I did some power-on tests to see if there was any overshoot and detected none across the voltage range.

I checked the voltage and current against my 6 digit meter and it is accurate across the range.

I did have my spectrum analyzer on in the same circuit as the power supply during the tests and there was no interference through the lines that affected the spectrum analyzer.

issue:
the power cords did not fit the socket. I was able to use another one, but, it looks like there is a burr on both power jacks that prevents the included chords from plugging in.  I've contacted them about this.. i could just file the bur, but, really wanna see how they deal with the issue.

The included red and white leads are the split solid post plug type, not a spring type banana plug. so don't expect much from those, I will use others I have.

other than that, everything functions as you expect with no operational glitches that I see.

[M0HZH]

+1 for Korad / Tenma.

I use the Tenma 72-10500 which is the dual 30V/3A version. Outputs can be switched to series / parallel mode too, so you can turn it into a single 60V/3A or single 30V/6A PSU.

[Berni]

Oh and i did blow up one of those Korad supplies before.

It was actually Tenma branded (Since Farnell sells all of the cheep chinese gear under that store brand name) and it was being used as part of a automated test jig for cycling batteries and collecting data about it. The USB interface on the back of it is buggy, works most of the time but then starts missing/repeating/replacing commands every so often. Turned out the RS232 port with an external USB to RS232 dongle worked way better (So keep that in mind if you want to remote control your Korad, don't use USB)

So i set it up the test jig with a large 12V lead acid battery and let it run, worked fine for a while, so i went home after work. Then at about midnight before going to bed i remote connect into the PC running the show to check if everything is running as it should. But there i see the battery voltage is at 16V (This is way overcharged for lead acid) and the power supply was reporting a large current. Oh shit shit shit, something is not right. I'm essentially just putting amps into eletrolyzing water and filling the room with hydrogen. I take over manual control and crank up the electronic load as high as it goes to bring the battery voltage back down while i try to turn off the power supply. Well according to the voltage measured by the electronic load there was still power being output. At this point i was considering calling up a coworker that lives closer to go unplug it. Eventually i found out i can get the power supply to reduce its output by setting its output voltage to 1V rather than telling it to disable the output. So the situation was under control and i could wait til the next day of work to come unplug it and see what went wrong.

Looking trough the log files i found out that the PSU was charging the battery in constant current mode for about 30 minutes at 3 or 4A (forgot exactly) but then at some point the current reading started jumping about oddly for a few seconds before shooting up past 5A (And its only a 5A rated PSU) and stayed there. Looks like the log file has recorded the death of the PSUs pass transistors, making it output maximum beans. The reason why setting it to 1V made it better is this switches a transformer tap relay to the smallest tap.

Bringing the PSU back to my bench i tested it, and sure enough its outputting max voltage all the time, shorting the outputs would make it push 7 to 8A out of it no matter what the current limit is set to. So yeah indeed failed pass transistors. Made some photos to document it and sent it back under warranty and replaced the PSU in the test jig with a more reputable BK Precision PSU with USB control.

This is just a sample size of 1 however. Perhaps i happened to get a dud unit. Then again Dave managed to blow up a Korad in his video too. The thermal solution in these things is kinda wimpy and that heatsink does get rather toasty. So yeah i do not recommend running your Korad flat out for long periods of time, its possible that they overheat and blow up when drawing max current at a particularly unfavorable transformer tap vs output combinations. Its easy to fix if it does happen tho.

[Electro Fan]

As an admitted Korad fanboy I would say this about that.

There seems to be a bit of a consenus around here that, for example, an Aneng 8008 is a good meter for the price if you are doing DC and low voltage work but for AC and especially high voltage work Flukes and Brymens are better choices.

I think Korad power supplies, like the the Aneng 8008, offer excellent value for the price when used for the appropriate purposes.

The Korads are very suitable for powering electronics in the vicinity of 5V and probably to a lesser extent all the way to 30V but the suitability diminishes as you push the power supply higher through the transformer taps and higher in current.  To be clear I have no test data to confirm this.  My impressions are based largely on listening to the audible sounds the Korad KA3005P makes (and I’ve been listening for several years).  My impressions are that you could probably run at 5V and 3A for a long time (days? maybe weeks? maybe longer?) and the power supply will be fine.  As you push toward 30V and 5A I’m of the opinion that the reliable life of the power supply might be shortened vs relatively lower voltage and current settings and relatively shorter operating durations.

My experience with the remote control is limited but I think it can be described as functional rather than elegant - and as the voltage and current demands go further toward 30V and 5A I would rely on it less.  I’m pretty sure connecting the 3005 to a car battery for unattended operation is not one of the best use cases for a 3005.

IMO, what is a great use case is testing low voltage, maybe ~12V DC and typically 5V or less at 3A or less for minutes or hours or maybe days at a time.  The power supply is reasonably to very stable and durable in these ranges.  In my experience it is also pretty accurate - maybe within 1-2 hundredths of a volt and a milliamp or two throughout the full range of 0-30V and 0-5A.  The key point here is that the Korads are very good for enthusiast testing which typically involves powering various DUTs so as to get fairly accurate measurement readings over long enough durations to learn what causes what. 

Based on my experience I believe the Korad KA3005P and KA3005D are very good choices for measuring, learning, and basic to intermediate testing within the low to middle ranges of the 30/5 power specs for moderate durations (minutes, hours, and maybe days rather than weeks and months).  This is in contrast to using the power supply as a 24x7xforever powering / charging / load characterization product, especially toward the higher end of it’s specs.

I’m not saying a Korad KA3005P/D couldn’t run at 30V and 5A 24x7 but I’ve never tried and that probably isn’t it’s best use case.

An analogy is that the Korad is like an affordable, nicely performing, and very enjoyable sports car.  Used thoughtfully it could occasionally substitute for a station wagon but it’s not a truck.  At approximately $100 for the Korad KA3005D it would be hard to find a better linear power supply for testing.

[Berni]

That is the reason why i used it around about the 3A ballpark, i avoided using the PSU at the max 5A spec, i didn't really trust it to handle max load for longer periods of time.

Not saying that it is a bad PSU. I think it is a great value for money when it comes to an entry level PSU, indeed difficult to get anything better at this price point. But just so that you have its limitations in mind. I have a Aneng 8008 too, great little meter that is amazing value for money, but i also have other DMMs from Keysight,Agilent,HP,Keithley... some bench some portable. I like to keep a mix of both cheep gear and fancy gear, using it as appropriate.

The reason this Korad ended up on battery charging duty is that i got the task to throw together this test rig. But all the nice remote controllable PSUs ware used for something so i couldn't take them for a few days, so i just went and bought a cheap remote controllable PSU on Farnell with next day shipping. It was only needed for a few days to run these tests for development use, and it can be used as a simple small general purpose lab PSU afterwards. It worked great in the test rig (once i learned that the RS232 port is more reliable) going trough quite a few charge cycles on the small batteries, but then once the big lead acid battery was hooked up to measure its characteristics then the charge times went up a lot and so the PSU was sitting at the set current limit for a lot longer. The PSU has proven to be reliable for days on end, so i was not too worried about hooking up the big boatanchor of a lead acid battery they asked me to run on it. It still had the appropriate fuse fitted, the PSU had a external diode protecting from any possible back flow. Same fuse also protecting the electronic load in case that failed short, Vsense line on it had a separate smaller fuse etc. The internal construction of the Korad didn't look horrible or anything. i was not pushing it to the limit or anything, i had external protective measures in place, so i assumed its good enough to get the job done. Most test rigs i cobble together in a day to test something out are not perfect anyway, so i didn't think much of using a chinese PSU.

The chinese products can be impressively good when you find those hidden gems among the other cheap crap. And this Korad PSU is certainly one of those hidden gems, just be aware of its limitations.

[wizard69]

This has probably been asked a million times but here goes.

Yes but there are a million possible answers.
[quote
I’ve been searching Amazon for a cheap bench PSU. Just for getting back into the game really, mainly playing with STM32, Arduino stuff an the like. Don’t want to spend a mint as I am not sure how much it will get used.
[/quote]
This immediately sent up red flags.   Let me put it this way DO NOT BUY A BENCH POWER SUPPLY then.  It can be a terrible waste of money for somebody starting out or just getting started in electronics.   Yes they are very nice to have but you would know in less than a year if you can justify one and actually make use of the investment.

Contrast this with buying a quality DVM.   OK so you loose interest in microprocessor projects for a time, even if that happens a multimeter is a good tool to have in ones tool box.   I learned this the hard way after finishing tech school and changing jobs thinking that the company would supply the tools I need.   What I missed is that it is very handy to have such an instrument at home for projects and repairs.   I can't really say that a bench power supply fills that role.   So I ended up buying a new one soon after selling the old one.

So you may ask how do you power your projects.   For miroporcessors you can start out with simple 3 terminal regulators at the right voltage and a few discreet parts.   YOu need nothing fancy to power up a microprocessor (at least a modern one).   Beyond that there is a lot that can be learned from a power supply build.

Any recommendations and any specific features that would be good to have? Years ago I just used a self modified CB PSU that would go from 3v-15v so I have never really had a proper bench PSU hence the lack of knowledge.

Well here is the thing, you will likely end up need more than one if your interest in electronics blossoms.   So keeping that thought in mind here i what I would suggest for a first supply, with the thought that you buy it once you are fairly sure it will be used:

• The supply should support three channels of output.
• There should be one channel that supports the minimal range of 1 to 6 volts DC for the microprocessor supply.   This should be at least 1 amp and it be nice if it went to 3 amps.   I wouldn't mind if the voltage here was semi fixed.  In the old days you could buy bench supplies with a fixed 5VDC output along side the two variable supplies, that doesn't work with today's various microprocessors and their operating voltages.   Thus you want this supply to be variable across the common range of microprocessor operating voltages.
• There should be two variable, "high voltage" supplies that do 0 to 30 volts DC or so.   One amp should be plenty.
• The two high voltage supplies should have digital displays with both voltage and current possible.
• The low voltage supply ideally would have its own displays also.   However this isn't as big of a deal as you generally would want to set the voltage of this supply and have it be very difficult to adjust.
• There is an interesting comment about pots and accidental adjustments, that is a real issue but I like pots or encoders to twist.   All I can say here is that if the low voltage supply for the microprocessor is hard to adjust you prevent a lot of problems.   Meanwhile encoders (preferred) or pots allow you to ramp up a voltage output in a very human way so are preferred in my mind for the high voltage supplies.   I seem to remember some manufacture addressing accidental adjustment with a lock out feature.  In any event yeah I like knobs!
• Obviously you need current limiting on all channels.
• Ideally the supply is protected against reverse voltages
• A battery charge mode might not be a bad thing if you are into lithium batteries.
• Support for communications with a PC.  Maybe not important if you are not into programming and data collection but with modern hardware it is hardly expensive to implement.
• Displays that are easy on the eyes!   This is one of those things where modern displays are trumpeted as ideal but they are not so ideal if you can't read them.   Old LED displays can be a better choice for readability especially if your supply is not front and center.   Since some LCD's are better than others it would be nice if you could take a look before purchase.   However that likely isn't possible.   You should ask yourself if the display is on the top shelf of the bench or off in some odd location, will you be able to read it sitting at the bench.

In any event just some thoughts that come to mind if I was in the market for a bench supply.   I'm not even sure if you could find a supply today that has all the features I highlighted above.   Knobs seem to be out of style on many supplies these days for example.   I really believe a semifixed microprocessor supply (low voltage supply)  makes a lot of sense simply to avoid the accidental adjustment of death but most supplies these days make that supply very adjustable.

[cdev]

used equipment is so cheap there is no reason not to get a small power supply with the most important thing being adjustable current and voltage. If you do do experimenting, this will pay for itself by preventing mistakes from destroying your valuable parts.

Also, from experience, a totally silent power supply is very preferable to one that makes noise as far as usability even if the voltage/current it delivers is much lower.

You can quite possibly also convert a PC power supply to adjustable voltage and current with one of those buck/boost modules. 

[Trader]

There are some bad reviews on Amazon about the KORAD PSU.

"Set to 3.5V and was powering a rather expensive board. When turned the supply off, it blew up his board. Hooked up the oscilloscope to measure the voltage when the supply is turned off, appeared spikes that were more than twice the voltage setting."

"Scope trace captures an unsafe voltage transient that occurred on the output terminals after the output was disabled, when the power supply power switch was turned off. These transients are 70V peak-to-peak. Tested 4 units in our lab that all do the same thing, (though with inconsistent magnitude) so we are looking for a different model supply that doesn't jeopardize our units that we are testing. When the output is disabled, no voltage applied on the output terminals is acceptable, let alone +/- 35 Volts!"

[AaronLee]

"Set to 3.5V and was powering a rather expensive board. When turned the supply off, it blew up his board. Hooked up the oscilloscope to measure the voltage when the supply is turned off, appeared spikes that were more than twice the voltage setting."

I got in the habit long ago of putting a separate switch inline on the leads from my power supplies, and turn on the PSU with the inline switch off, then turn power to the board on/off with the inline switch. When done, turn off the inline switch, then the PSU. Even some of the name brand PSUs seem to have issues with overshoot, and the inline switch gives me more peace of mind. Not sure if it's ever saved me or not though.

[mawyatt]

Even some of the name brand PSUs seem to have issues with overshoot, and the inline switch gives me more peace of mind. Not sure if it's ever saved me or not though.

We are working with some very expensive sensitive chips and concerned about PS issues, we ordered the Siglent SPD3303X-E to evaluate. We now have 3, and maybe will be ordering another. One concern was overshoot at PS turn on or turn off and these Siglent PS don't exhibit any bad behavior and well suited for lab use IMO. Long ago had an experience with a name brand PS having overshoot at turn on, this destroyed a couple very expensive custom chips before the overshoot was discovered

Best,

[MultiMike]

Even some of the name brand PSUs seem to have issues with overshoot, and the inline switch gives me more peace of mind. Not sure if it's ever saved me or not though.

I recently bought a TopShak LW-3010EC from.. probably Banggood.  It was pretty cheap, but it had the important requirement: an 'output' button, so that you don't have to short to leads to set the volts and amps.   I realize it's not a perfect test, but if it's jumping the voltage at turn-on or turn-off then my meter can't see it.

Mike

[Berni]

"Set to 3.5V and was powering a rather expensive board. When turned the supply off, it blew up his board. Hooked up the oscilloscope to measure the voltage when the supply is turned off, appeared spikes that were more than twice the voltage setting."

I got in the habit long ago of putting a separate switch inline on the leads from my power supplies, and turn on the PSU with the inline switch off, then turn power to the board on/off with the inline switch. When done, turn off the inline switch, then the PSU. Even some of the name brand PSUs seem to have issues with overshoot, and the inline switch gives me more peace of mind. Not sure if it's ever saved me or not though.

No competent lab PSU should have trouble with overshoots on turn on or turn off. Relegate such a PSU to being used as a battery charger or something.

But even if the inline switch saves you from the turn on overshoot it won't save you from a unstable regulation loop. Circuits often have a good deal of capacitance on its power rails, suddenly applying that to a PSU output will cause a very large output current transient. If it's an unstable loop causing overshoots then this current spike might also cause the PSU to overshoot the output voltage. (Especially since the PSU can't sink current and has output capacitance that can take a while to go back down)

It's not hard to test for overshoot with a scope, so its worth doing. Mindful of also doing this with a large load resistor or large capacitor across the output.

The Chinese can make a pretty decent linear PSU if you look around. Tho one should be careful running them near rated max for long periods as they often lack the required cooling for it. The thing to absolutely stay away from are switchmode bench supplies. They look enticing with the large outputs of say 10A and more while being tiny. But every single one of them i have seen barfs out noise like its designed to be a radio jammer. They are fine for running high power loads like heaters and motors, but they are NOT suitable for powering electronics on your bench.

EDIT: Not to say switchmode bench supplies are crap in general. The well made ones from the big well known test equipment manufacturers are actually impressively low noise. Tho they are very expensive, so your best bet on those is to pick up a old rack mount one on ebay.

[Adrian_Arg.]

Trader, I have a Uni-t 0-30v 0-5a Utp3315tfl-ii Dimmable Laboratory Source, which in general terms works well, I reduced the fan noise by lowering the voltage to 12V with a DC-DC source, that way the I regulate, due to the problem of peaks when turning the equipment on and off, I make sure that nothing is connected.

in spanish
Trader, yo tengo una Fuente Laboratorio Regulable Uni-t 0-30v 0-5a Utp3315tfl-ii, que en terminos generales funciona bien, el ruido del ventilador lo reduje bajando el  voltaje a 12V con una fuente DC-DC, de esa manera la regulo, por el problema de los picos al encender y apagar el equipo me aseguro que no haya nada conectado.

[mawyatt]

No competent lab PSU should have trouble with overshoots on turn on or turn off. Relegate such a PSU to being used as a battery charger or something.

But even if the inline switch saves you from the turn on overshoot it won't save you from a unstable regulation loop. Circuits often have a good deal of capacitance on its power rails, suddenly applying that to a PSU output will cause a very large output current transient. If it's an unstable loop causing overshoots then this current spike might also cause the PSU to overshoot the output voltage. (Especially since the PSU can't sink current and has output capacitance that can take a while to go back down)

It's not hard to test for overshoot with a scope, so its worth doing. Mindful of also doing this with a large load resistor or large capacitor across the output.

The Chinese can make a pretty decent linear PSU if you look around. Tho one should be careful running them near rated max for long periods as they often lack the required cooling for it. The thing to absolutely stay away from are switchmode bench supplies. They look enticing with the large outputs of say 10A and more while being tiny. But every single one of them i have seen barfs out noise like its designed to be a radio jammer. They are fine for running high power loads like heaters and motors, but they are NOT suitable for powering electronics on your bench.

EDIT: Not to say switchmode bench supplies are crap in general. The well made ones from the big well known test equipment manufacturers are actually impressively low noise. Tho they are very expensive, so your best bet on those is to pick up a old rack mount one on ebay.

We stay away from switchers of any kind for general purpose lab use, have never found one that wasn't noisy. We do have a few switch-mode supplies for things like power LED or motors use, and a couple HV switch-mode supplies to provide specific HV needs.

The overshoot is caused by an underdamped response, not an unstable response. A good PS should be overdamped in all usages, with all expected loads, real or reactive. Using a scope to verify your PS at turn-on and off is a wise move, since a DMM likely won't show this.

We've found the Chinese Siglent SPD3303X-E a decent lab supply, and after evaluation entrusted it with our development project where a single hiccup could destroy well more than the supply cost!!

If one is involved with electronics development work, the PS is the most important piece of test equipment on your bench. How are you going to verify the circuits performance without a good, clean and stable supply input as a baseline

BTW I think it's funny how we often cheap out on the power supply, or test leads, or scope probes, and I am as guilty as anyone. Something about the "lure" of a bargain set of test leads, or a wide-band scope probe, or a nice new looking power supply, that one just can't resist. This must be some sort of "Engineering Addiction" and the "Rehab Centers" are the established quality suppliers

Best,

[AaronLee]

Just a few months ago, Dave did a teardown of the new R&S power supply which had an overshoot problem:
https://www.eevblog.com/forum/blog/eevblog-1402-rohde-schwarz-nga100-psu-teardown-giveaway/

That's definitely in no way a cheap power supply, and R&S is a well trusted brand name. I actually was considering buying that power supply, but to spend that kind of money and still have overshoot, I decided to save my money and went with a Siglent PSU instead and spend the remainder on other gear I needed.