EEVblog #404 - Korad PSU Followup

[EEVblog]

Dave.

[JoannaK]

Nice bundle for anyone needing that kind of stuff.

[SeanB]

New output devices and a much easier to service respin on the board. Now you can unsolder the devices and remove the board, then replace them and feed the leads in after assembly.

[EEVblog]

Nice bundle for anyone needing that kind of stuff.

Someone suggested a charity ebay auction, sounds like a plan.

Dave.

[LEECH666]

So Dave, what made you reconsider your opinion on the Korad PSU? This quick video sounded rather positive (calling it a "winner"). I was under the impression that you didn't want anything to do with it anymore after Korad kept coming up with excuses/delays over and over again.

Just curious ...

Florian

[EEVblog]

So Dave, what made you reconsider your opinion on the Korad PSU? This quick video sounded rather positive (calling it a "winner"). I was under the impression that you didn't want anything to do with it anymore after Korad kept coming up with excuses/delays over and over again.

Charles tested the new one, and it seems to perform as expected (hence the word "winner"), see his video. As it did when I tested it until it failed, which they seem to have now, finally, fixed. If it didn't fail when I tested it, it would have gotten a good review.
Yes, we are not happy with Korad about their response and communication,  and I have no interest in reviewing it myself again as result. But that opinion doesn't change the fact that the unit, as it stands, seems to be good bang-per-buck at that price point. As always, YMMV.

Dave.

[firewalker]

Link of the video.



Alexander.

[LEECH666]

Actually I considered bying the Korad, even tho it blew up on your bench, Dave. It goes for ~100€ at the Polish distributor www.hotair.pl , which makes it even more attractive (if you don't mind waiving support), imo. The only reason I didn't buy it yet is because I bought some other really cheap "lab" PSUs. I might do a limited review of them soon.

[EEVblog]

BTW, I tweeted that I will be getting one of these in few days:
http://www.attenelectronics.com/Products/Power_Supply/Programmable_power/2012/0728/89.html

AU$469
Will be interesting to see what it's like.

Dave.

[EEVblog]

Actually I considered bying the Korad, even tho it blew up on your bench, Dave. It goes for ~100€ at the Polish distributor www.hotair.pl , which makes it even more attractive (if you don't mind waiving support),

Exactly!

Good quality PSU's (e.g. Agilent) are very expensive, so often you have to go for the best bang-per-buck you can find.

Dave.

[AndyC_772]

They do occasionally come up on Ebay, though. That's how I've ended up with 3x HP 6632B's on my bench 

[maor]

Does TrioSmartCal sell the new version already? and do they do worldwide shipping?

[EEVblog]

They do occasionally come up on Ebay, though. That's how I've ended up with 3x HP 6632B's on my bench 

Pretty rare here in Oz unfortunately to get good HP supplies, and when they do come up, go for a pretty penny.

Dave.

[EEVblog]

Does TrioSmartCal sell the new version already? and do they do worldwide shipping?

It's on their website and are available.
They probably can ship, ask them, but it will likely cost a LOT.

Dave.

[somlioy]

BTW, I tweeted that I will be getting one of these in few days:
http://www.attenelectronics.com/Products/Power_Supply/Programmable_power/2012/0728/89.html

AU$469
Will be interesting to see what it's like.

Dave.

Oh, that certainly looks like an interesseting power supply. Maybe I'll wait for that review before buying myself a power supply.

[Rick]

They do occasionally come up on Ebay, though. That's how I've ended up with 3x HP 6632B's on my bench 

If it's not a secret, how much have you paid on average for each one?

[AndyC_772]

They all came from the same guy in Finland, and ended up between about £150-£170 each including shipping:

http://www.ebay.co.uk/itm/221123189659

He had a whole bunch to sell - I'm guessing a factory closed down, perhaps - and advertised them in batches over the course of the year. Sadly I've not seen any more recently, though it might be worth dropping him a note to ask if there are any more likely to become available. They all worked fine and were accurately calibrated.

[AndyC_772]

Pretty rare here in Oz unfortunately to get good HP supplies, and when they do come up, go for a pretty penny.

Dave.

I guess it's the shipping cost that's the killer. The 6632B is *heavy*.

[Michal]

Hi Dave.

Is there any label with version number on the PSU? Can we see a photo of it or see it on your next video?? I wonder about buying one.

Michal

[george graves]

Ask the seller - most will know their stock.

I think I'm going to buy two of these this week.  It's 1/6 of the price of a HP unit, and I love the interface.

[Michal]

Ask the seller - most will know their stock.

Thanks for your advice but I don't know which production version is the new one. So I'm pretty sure that seller won't give me any help.

[TRIO_Smartcal]

All ours are modified stock. Plus all our stock has been tested by us for short circuit test and a ramp up to full load test.

We are not the cheapest resellers of these in the world and I'm well aware of that. Our volume in the Aussie market is not high so our cost to get them here by air is not the lowest either and this shows up in the sales price. We don't import stuff by sea as the risk is too great.

Included in our price is a 2 year warranty and Dave knows where we live!!

The only place we ship to now outside Australia is New Zealand.

I can look at the costs to ship to Europe. We use DHL or TNT.  I'll post  the cost to the London area on here as a guide when our logistics manager returns from Christmas leave on the 7th Jan.

[SeanB]

Probably in the region of $ 70 per 5kg parcel, as that is a pretty common cost for international courier, with a 10kg limit normally. Triple that for a "Hazardous" cargo. ie one with lithium primary or secondary cells, compressed or flammable gas or any flammable liquid or anything containing either listed chemicals or strong acids or bases.

[opticpow]

Hi Dave.

Is there any label with version number on the PSU? Can we see a photo of it or see it on your next video?? I wonder about buying one.

Michal

Michal,

I think your bet bet is buying from somewhere you trust. Yes, it might not be the cheapest place but you know you will backup incase something gones wrong, and with this supplies short history, well worth it IMHO. I ordered one from Trio just before Xmas, and I'm a happy first time customer. Seeing how they reponded to the issue tells me everything I need to know.

Cheers,

Wayne.

[David_AVD]

I ordered mine from Trio yesterday.   

[Michal]

I am from Poland, that is in Europe.  So that wouldn't be the best solution for me to buy something in the Australian market.

Please give me some info if there is a sticker with printed version number of the PSU shown in EEVblog #404. If not, please write so. That would help me buy the newer one.

Hmm....

All ours are modified stock. Plus all our stock has been tested by us for short circuit test and a ramp up to full load test.

How to understand that. TRIO is modifying these PSU's and I won't buy one in the European market or what?

I'm confused now.

[HackedFridgeMagnet]

It seems Trio is upgrading all its existing stock to the new version.
Other distributors in other parts of the world may not be doing this, you will have to ask them or Korad directly.
Any stickers on the Korad boxes that Trio are selling probably wont help you identify old versions from upgraded versions.
You will probably need to see or see photos of inside the box to be sure.

[Michal]

So is the upgrade TRIO's own project? Or they've got KORAD's spare parts to replace? Anyway, that's really unusual situation.

[EEVblog]

So the upgrade is TRIO's own project? Or they've got spare parts to replace? Anyway, that's really unusual situation.

No, it's an official board set sent from Korad, after they investigated the issue and (it seems) fixed it.
They sent the new boards Trio because they complained that they got dud supplies.
Whether or not Korad will actively do the same with other suppliers and ship them boards too, I don't know, you'll have to ask them.
And I can't imagine every supplier being willing to strip the things down and refit boards themselves. Trio are doing this off their own bat.
It is most likely that all existing stock out there is the old batch.
But I would like to think that any new stock coming from Korad is the new design.
Also, we don't know if any 110V versions have the same issue.

Dave.

[alm]

My take on it is that the service from Korad sucks, even Trio Smartcal had problems getting anything out of them. They're much more likely to listen to Trio than to a random consumer, however, since they represent a much larger sales volume. I would be hesitant to buy Korad products without a good distributor to handle any issues for me. Support might very well be non-existent.

[EEVblog]

My take on it is that the service from Korad sucks, even Trio Smartcal had problems getting anything out of them. They're much more likely to listen to Trio than to a random consumer, however, since they represent a much larger sales volume. I would be hesitant to buy Korad products without a good distributor to handle any issues for me. Support might very well be non-existent.

Well, when you buy from a reputable distributor, then that's what you are paying extra for, that extra piece of mind. They are the ones that will usually fix any issues for you, regardless of how good/bad the manufacturer or product might be. Some dealers for example offer their own extra warranty, and if it fails outside the manufacturers warranty (or they have trouble getting the manufacturer to support the warranty) then they are the ones that eat it.

Dave.

[alm]

But in the case of a reputable manufacturer like Fluke, you can always go back to the original manufacturer if the distributor is unable/unwilling to help you. In the case of Korad, the distributor might be your only hope. I would be much more willing to buy a Fluke DMM from a distributor with lousy support than a Korad power supply.

People used to say about 3Com network interface cards that no where you found it, even if you picked it out of the garbage, if it didn't work you could send it to 3Com and they'll give you a working one. With that kind of manufacturer support, who needs distributors?

[EEVblog]

But in the case of a reputable manufacturer like Fluke, you can always go back to the original manufacturer if the distributor is unable/unwilling to help you. In the case of Korad, the distributor might be your only hope. I would be much more willing to buy a Fluke DMM from a distributor with lousy support than a Korad power supply.

People used to say about 3Com network interface cards that no where you found it, even if you picked it out of the garbage, if it didn't work you could send it to 3Com and they'll give you a working one. With that kind of manufacturer support, who needs distributors?

A local dealer will often give you instant service, and local of course. i.e. if it fails, you walk back in the door and they will likely just give you a new one instantly (or a loaner), and they are left to sort out the details, not you.
Few manufacturers are going to offer that kind of service, and they usually aren't local. Good luck if you are overseas without a local manufacturers office...

Dave.

[alm]

If the equipment is sufficiently complex, then the only thing the dealer can do is to sit on the equipment for an extra week before sending it off to the manufacturer. Best case is that you get it back just as fast as if you'd have shipped it yourself, and you save on shipping costs. Worst case is that they attempt to replicate an intermittent problem, fail, and send it back to you as 'fixed'. The fasted way to deal with this is to include a note to the effect of 'please send this directly to the manufacturer referencing technical bulletin #'.

If the manufacturer is unwilling to help, then a good dealer might give you a replacement or (partial) refund. If the manufacturer is unresponsive, then the dealer might do the screaming and calling several times per day work for you. That's when a good dealer is important.

[Michal]

I sent email to my local distributor, hotair.pl. I hope they're fixing these PSU's to. Or maybe they have the new ones from Korad on the stock.

[Bored@Work]

A local dealer will often give you instant service, and local of course. i.e. if it fails, you walk back in the door and they will likely just give you a new one instantly (or a loaner), and they are left to sort out the details, not you.

Local dealers have the nasty habit of going out of business, especially in the current economic climate.

Even if they are still around, here local dealers have a very special local habit, letting you jump through all sorts of hoops before they even consider lifting a finger. Irrespective of what the contract says, what the law says and what warranty they promised, typically there first response is to point to the manufacturer and then go silent.

Dealing with the middle man is a pain here. And that's why direct manufacturer support is a must for me. And that is why I don't have much good to say about the likes of Rigol, Hantek, Uni-T or even GW-Instek. No, I don't care if they have a walk-in repair center at the other side of the word, a service phone number for China or instant support in the US.

[Michal]

I got answer from hotair.pl. They said this is the old problem with KA3005P an they sold out all their PSU's (new ones). I've got to wait two weeks for new shipment and then buy.

Happy New Year !!!

[Polossatik]

They all came from the same guy in Finland, and ended up between about £150-£170 each including shipping:

http://www.ebay.co.uk/itm/221123189659

He had a whole bunch to sell - I'm guessing a factory closed down, perhaps - and advertised them in batches over the course of the year. Sadly I've not seen any more recently, though it might be worth dropping him a note to ask if there are any more likely to become available. They all worked fine and were accurately calibrated.

just fyi: i contacted the seller and he said when asked if there where more: "Hi , I may get more of them in the near future. I'll check the stock when I get back to Finland, I'm just now abroad."

[UPI]

FYI - Here is what I received from SRA (through Amazon) on December 28th 2012.

It seems to have some but not all updated parts.

The transformer still says 220V and I don't see the "bodge" capacitor. Everything else looks updated.

[george graves]

Look like they are also selling a two unit version with an added 5v 3 amp out.

I  can just see one side blowing up, and you'd be stuck with both on your desk.

[ivan747]

I think they just provided a 240V country, Australia, with 220V transformers. The transistors were already at their maximum ratings and after getting the extra 10-20 volts they failed. American ones should come with a 220/110 volt transformer because they use 110V. Maybe that's why Australian ones have the new power transistor board.

[IanB]

Actually, no. America is a 120 V country as I mentioned above. If you are not getting 120 V out of your receptacles you are being short changed by your power company.

[JackOfVA]

We started out as a 110V country, thanks to Tom Edison. He picked a nice round number, 100V for DC distribution, and then added 10%, 110V total. The first AC systems maintained the 110V DC standard (in VAC RMS, of course), and over time the nominal distribution voltage has crept upward as (a) it permits more efficient use of the distribution network and (b) it allows the power company to sell more electricity.

If one wishes to be more pedantic, Edison's original DC system was actually +/- 110V, with a neutral/ground. But from what I recall reading, only 110V was made available to customers, some got +110V and others -110V and none had 220V DC.

If you look at old equipment nameplates or catalogs, you will see the nominal line voltage stated as 110V (really old), 115V, 117.5V and now 120V. My line voltage used to run 123-124V but after the power company reworked its local distribution network a couple years ago, it's almost always within 1V of 120V.

My UPS power supply has trip points at 135V / 95V, and within that range it will not switch to inverter.

[george graves]

That's interesting....cause house hold outlets are 120 - but if you have a dryer outlet it's usually refereed to as a 220 - not 240.  At least that's what it's called.

[mickpah]

wiki to the rescue again http://en.wikipedia.org/wiki/Mains_electricity_by_country , looks to me that the majority of the world is using 220-240 including China at 220v.
If I was looking looking to market a global product 230v +/- 10 % looks to be a nice fit and a 110V version for those who like big think mains cables and have the money for all the extra copper in the walls

[saturation]

The US is typically 240V or more multiphase AC distributed to customers, however within dwellings 240V are split into 2 branches, each with 120V and converted to single phase.  Large appliances in the US are typically 240V; water heaters, central airconditioners, etc., .

http://en.wikipedia.org/wiki/Mains_electricity#History_of_voltage_and_frequency

[jancumps]

I've got 3-phase + neutral at home. The previous owner had heavy machinery.
I can take 400V  between two phases, and 230V between phase and neutral.

[saturation]

The real difference between 120V and 240V is mostly is in-room wiring, much less how the power company distributes power.  Naturally, the other difference is the line frequency.

The 120V system used in the US  uses smaller diameter wires for room distribution vs say the UK, its typically 14 AWG ~ 2mm^2, compared to UK code which requires 4mm^2.   Although the wire diameters evntually vary depending on distance from the distribution panel and what the appliance its expected to serve, these wires are typical for mains receptacles.

http://en.wikipedia.org/wiki/Electrical_wiring_in_the_United_Kingdom

http://en.wikipedia.org/wiki/Electrical_wiring_(US)

wiki to the rescue again http://en.wikipedia.org/wiki/Mains_electricity_by_country , looks to me that the majority of the world is using 220-240 including China at 220v.
If I was looking looking to market a global product 230v +/- 10 % looks to be a nice fit and a 110V version for those who like big think mains cables and have the money for all the extra copper in the walls

[mickpah]

ahh, as always the devil is in the detail.
 In Australia at least a circuit protected by a circuit beaker can have  20 power outlets , each rated at 10 amps (in practice this is 10 points each with two sockets) protected by a 15A breaker using 2.5 mm² cable. This is subject to  derating factors for how the cable is run but it a good starting point for discussion. I have no idea what the wiring rules are in the US, so will leave that for others.

Can't beat ohms law.
2kW resistive  at 240v = 8.3 amps  , 2kW resistive  at 110v = 18.2 amps , no getting around the fact you need the copper in the walls to carry the load if you don't want voltage drop and heat loss ( fire).

[Monkeh]

The 120V system used in the US  uses smaller diameter wires for room distribution vs say the UK, its typically 14 AWG ~ 2mm^2, compared to UK code which requires 4mm^2.

Please don't talk out your arse. UK 'code' requires nothing of the sort.

120V systems wired in the US manner use far more copper. That's an unavoidable fact.

[xani]

Does anyone have experience with triple ( KORAD KA3005D-3S 2x(30V 5A)+5V ) version of that power supply ? I

[poundy]

Is the switch-on behaviour of the "new" PSU still showing the same transients and overshoot in the combinations the original test showed?

[uoficowboy]

I recently picked up the Korad KA3005D on Amazon. It seems to work well, except for a couple of quirks:

1. The power button doesn't work all the time. It gets stuck on. I just attempted a rework of the switch and I *think* that has fixed things, but I'm not positive of that. The switch appears to be a Chinese copy of the E-switch P197EESB. So if the problem reoccurs, I'll just replace it with that one.

2. Whatever is driving the display is not super smart. I occasionally use it to charge LiPo batteries. I'll set a current and a voltage (say, 50ma and 4.2V). For most of the time, it'll properly display the voltage and current (ie 50ma and 3.8V). But as it approaches the set voltage (4.2V) it'll switch over to displaying the set voltage, instead of the output voltage. So, this is what I just saw about 5 minutes ago:

50ma 3.8V CC (measured voltage: 3.8V)
50ma 3.9V CC (measured voltage: 3.9V)
50ma 4.0V CC (measured voltage: 4.0V)
50ma 4.2V CC (measured voltage 4.05V)
50ma 4.2V CC (measured voltage: 4.1V)
40ma 4.2V CV (measured voltage: 4.2V)
30ma 4.2V CV (measured voltage: 4.2V)
etc (I'm simplifying here, obviously)

The switchover seemed to be around the 4.01V mark. I even saw the display oscillating there - between 4.01 and 4.2V (where 4.01V was the correct voltage). Anybody else seen this?

3. The current measurement has a small offset to it - maybe 4ma. Anybody know of any clever way to calibrate this thing? I often operate at low currents, so it'd be nice to get rid of that offset!

Overall, this is a great supply for the money IMHO.

[Huluvu]

The switchover seemed to be around the 4.01V mark. I even saw the display oscillating there - between 4.01 and 4.2V (where 4.01V was the correct voltage). Anybody else seen this?

3. The current measurement has a small offset to it - maybe 4ma. Anybody know of any clever way to calibrate this thing? I often operate at low currents, so it'd be nice to get rid of that offset!

I never ever would rely on the displayed values shown by an Power Supply if I need really accurate readings.
Most power supply's are not calibrate able and the confidence level is very low.

[uoficowboy]

The switchover seemed to be around the 4.01V mark. I even saw the display oscillating there - between 4.01 and 4.2V (where 4.01V was the correct voltage). Anybody else seen this?

3. The current measurement has a small offset to it - maybe 4ma. Anybody know of any clever way to calibrate this thing? I often operate at low currents, so it'd be nice to get rid of that offset!

I never ever would rely on the displayed values shown by an Power Supply if I need really accurate readings.
Most power supply's are not calibrate able and the confidence level is very low.

My main concern is not that the displayed voltage is inaccurate - rather that the displayed voltage is the set voltage, not the output voltage, when in current limiting mode and your output voltage is close to the set voltage. This is almost for sure a software bug.

On a side note - I replaced the power switch and the device turns on and off reliably. A colleague later showed me a way of tweaking the contact inside the button to make it springier so if anybody else has this problem the original switch may still be salvageable.

[Rasz]

My main concern is not that the displayed voltage is inaccurate - rather that the displayed voltage is the set voltage, not the output voltage, when in current limiting mode and your output voltage is close to the set voltage. This is almost for sure a software bug.

Mmm sounds familiar. This is most probably not a bug, but a way chinese do it.
I have cheap Chinese knockoff RKC REX C-100 ($14) Controller and its exactly the same, as soon as it approaches SET temperature it starts to lie in your face about its super duper stability/accuracy. It almost makes me think its an Asian thing (mm sweet racial discrimination). Those products lie just like Japanese Businessman/Government official would - shaking your hand, nodding his head and lying straight in your face because its more honorable to lie than to admit defeat.

[MBY]

The switchover seemed to be around the 4.01V mark. I even saw the display oscillating there - between 4.01 and 4.2V (where 4.01V was the correct voltage). Anybody else seen this?

3. The current measurement has a small offset to it - maybe 4ma. Anybody know of any clever way to calibrate this thing? I often operate at low currents, so it'd be nice to get rid of that offset!

I never ever would rely on the displayed values shown by an Power Supply if I need really accurate readings.
Most power supply's are not calibrate able and the confidence level is very low.

My main concern is not that the displayed voltage is inaccurate - rather that the displayed voltage is the set voltage, not the output voltage, when in current limiting mode and your output voltage is close to the set voltage. This is almost for sure a software bug.

On a side note - I replaced the power switch and the device turns on and off reliably. A colleague later showed me a way of tweaking the contact inside the button to make it springier so if anybody else has this problem the original switch may still be salvageable.

Thats a serious issue and a complete show-stopper! Can more people please try to confirm this?

[Mdbelen]

Hi, i can still confirm this issue with my unit (KA3005P), just recently ordered from hotair.pl. (Btw they sadly put stickers on some case screws so I can't open it without losing warranty.)
I tried with 1 and 3S 1W LEDs = 3 and 10V and for both there was a gap of 200mV. This is a >5% error for low voltages. Pretty damn much for a claimed accuracy of 0.5%+20mV! What a retarded software """feature""".

To summarize misbehavior in few a words:
If in CC-mode V_real approaches V_set to (V_real = V_set - 0,2V) the display switches from displaying V_real to display V_set.
This does not happen for the displayed current in CV-mode though.

Another notsonice fact i discovered:
OVP does not trigger reliably for me: If OVP is enabled and output is open looped it does not trigger (though ofc V_real=V_set). Also if I slowly increase the current through a load until V_real reaches V_set it does not trigger, no matter how much further I increase C_set. It does only trigger if I increase the C_real pretty fast, thus "shoot" in the V_set limit pretty fast.
Don't know how much this matters in practical usage, as OVP won't be used often anyway I guess.

3S=3 in series | CC=constant current | CV=constant voltage | C=current | V=voltage