Korad display bug

[Maxlor]

I've noticed a display bug with my Korad KA3005P (well, Velleman relabelled) power supply. I had been using it to charge a Lipo Cell, with voltage limited to 4.20V, and current limited to 0.5A. The display on the PSU correctly indicates e.g. 3.90V/0.5A/CC while the battery is still fairly empty. However, once the voltage rises to around 4.05V, the display jumps to 4.20V/0.5A/CC. Actual voltage at the output jacks is still 4.05, or slightly above it. In other words, the voltage reading is wrong, displaying the set voltage instead of the actual voltage when that is near the set voltage. Performance seems unaffected, current control remains in effect and the current control/voltage control switchover happens as it should.

Is it just my unit that has this fluke, or can other people see this too?

[hexreader]

I have the same Vellemann supply.

Whilst I love my unit, and it is fantastic value for money, I would not trust it in any way.

Accuracy is poor at the best of times, and Dave has video reviews of Korad PSU versions from the early VERY buggy units through to the improved versions.

It is a very cheap, low quality supply. I think you are expecting too much of it.

If it charges your batteries, then great...  that is a good use for it.

If you want accuracy, reliability and quality - spend more money on a branded supply (or at least attach external voltage and current meters that can be relied upon)

What you are seeing sounds like pretty good performance for such a cheap unit.

.... just my thoughts...   feel free to ignore

[jaxbird]

I have the same Vellemann supply.

Whilst I love my unit, and it is fantastic value for money, I would not trust it in any way.

Accuracy is poor at the best of times, and Dave has video reviews of Korad PSU versions from the early VERY buggy units through to the improved versions.

It is a very cheap, low quality supply. I think you are expecting too much of it.

...

Had the Korad branded unit from just around Dave's review, I agree it's exceptional value, not sure what the cost is today, but so far it's served me well (much beyond my expectations actually). In my experience it's been fairly precise, give or take a few mA or a few 10s of mV across the whole range it's been pretty much spot on.

I believe the issue described by Maxlor is an actual software display issue, not just due to lack of accuracy, in my experience it can go a bit funny when both setting a voltage limit and a current limit , but not something I've found a big deal. I don't expect this to be fixed in any updates, but looking on the bright side, it sounds like the psu is doing the right thing just not displaying the measured values when they are very close to the set values.

[Zbig]

I believe the issue described by Maxlor is an actual software display issue, not just due to lack of accuracy, in my experience it can go a bit funny when both setting a voltage limit and a current limit , but not something I've found a big deal.

That's actually what you should always do, IMO - setting the current limit and the voltage to not that much more than what you expect it to go given your current (I) limit. Or setting your current limit to the desired value and dialing the voltage up carefully until CC kicks in. Otherwise, you risk blowing your DUT up with the energy stored in the output filtering caps before it depletes, even after the regulation circuitry adjusts the voltage.

[Maxlor]

I have the same Vellemann supply.

Whilst I love my unit, and it is fantastic value for money, I would not trust it in any way.

Accuracy is poor at the best of times, and Dave has video reviews of Korad PSU versions from the early VERY buggy units through to the improved versions.

It is a very cheap, low quality supply. I think you are expecting too much of it.

If it charges your batteries, then great...  that is a good use for it.

If you want accuracy, reliability and quality - spend more money on a branded supply (or at least attach external voltage and current meters that can be relied upon)

What you are seeing sounds like pretty good performance for such a cheap unit.

.... just my thoughts...   feel free to ignore

In general, I'll have to disagree. While I'd not go so far to trust any expensive components to the values shown on display, I have no complaints about its accuracy, and I really like its precision, you won't find another programmable with this kind of resolution in this price class. I've checked its output under many different operation conditions since I got it last year, and it's never more than a few counts out. Ripple is fine too, overshoot could be better, it can be bad in pathological CV/CC switchover situations.

There are a couple of issues and weird design decisions, but I have yet to see another PSU with this performance and featureset in this price class. I am aware of course that I can get better equipment if I spend an order of magnitude more on it...

My original question remains open though. Is it just my unit that has this display bug where the wrong voltage is displayed near the CC/CV switchover point, or do others have it too?

[Andreas]

Is it just my unit that has this fluke, or can other people see this too?

I think it's a feature. I have this also with 0.5A and 18.1V setpoint. Above 17.89V the display jumps to 18.1V.
And even the current display seems to have similar (at least clipping) behaviour around current limit setpoint.

Otherwise the display is perhaps much too noisy.

With best regards

Andreas

[nixxon]

I've noticed a display bug with my Korad KA3005P (well, Velleman relabelled) power supply. I had been using it to charge a Lipo Cell, with voltage limited to 4.20V, and current limited to 0.5A. The display on the PSU correctly indicates e.g. 3.90V/0.5A/CC while the battery is still fairly empty. However, once the voltage rises to around 4.05V, the display jumps to 4.20V/0.5A/CC. Actual voltage at the output jacks is still 4.05, or slightly above it. In other words, the voltage reading is wrong, displaying the set voltage instead of the actual voltage when that is near the set voltage. Performance seems unaffected, current control remains in effect and the current control/voltage control switchover happens as it should.

Is it just my unit that has this fluke, or can other people see this too?

My new Velleman LABPS3005D (older unit is called PS3005D without the "LAB" prefix) does the same thing. I charge a 6V, 12 Ah Lead Acid battery with the power supply set to 7.2V and 2 Amps. As the Voltage on the power supply display passes 6.95V, the supply suddenly increases to the set voltage and displays 7.2V while still charging at 2.00 Amps, because the unit knows it displays to high a voltage. Why did they design it like this?? 

[Electro Fan]

If you haven't tried the calibration procedure it's worth a try.  My Korad KA3005P has remained reasonably accurate (or at least consistent) for more than 3 years since I followed the process.

https://www.eevblog.com/forum/beginners/korad-ka3005p/?action=dlattach;attach=61421

[CharlieWorton]

This power supply is selling for $211 CAD on Amazon.ca.  I chose it mostly on the basis of price vs features.  I've only just purchased the unit - still haven't thrown the box away - but I'm really pretty happy with it.  I've posted a (perhaps) overenthusiastic review on Amazon.ca at this link https://www.amazon.ca/KA3005P-Programmable-Precision-Variable-Adjustable-Regulated/dp/B0085QLNFM/ref=sr_1_1?ie=UTF8&qid=1496982811&sr=8-1&keywords=Korad+KA3005P as well as a couple images of the interior.  It really does look vastly superior on the inside to the one that Dave reviewed.  I'd actually like Dave to revisit this PSU, and check its accuracy and workmanship.  In his copious spare time, of course.  That one had terrible workmanship; but the new ones are pretty good.  At least, mine looks nice inside.  So if you want to see my power supply with its clothes off, follow the link. - Charlie

[astrand@lysator.liu.se]

I have the same problem. Calibration did not help 

[alm]

Are you guys using series diodes when charging? I wonder if there is some undershoot in the voltage limiting that draws current from the battery and confuses the supply. You will have to correct for the diode drop in your voltage setpoint, but at least the battery is less likely to kill the power supply.

[Yansi]

Interesting. Have two of those Korad units. None of them is crappy as that Dave reviewed (even using Nippon branded caps inside!)  and none of them has the problems above described. Using them to charge accumulators quite often with no problems.   So wtf?



After replacing the funny heatsink with bloody loud fan with a decent adequate heatsink and much slower fan, these two Korad supplies are working very well. No problems and I trust them no problem.

It most likely seems there might be quite some significantly different batches, or even fakes?

[pascal_sweden]

Can you indicate from where you ordered your "genuine" Korad power supplies?

Interesting. Have two of those Korad units. None of them is crappy as that Dave reviewed (even using Nippon branded caps inside!)  and none of them has the problems above described. Using them to charge accumulators quite often with no problems.   So wtf?



After replacing the funny heatsink with bloody loud fan with a decent adequate heatsink and much slower fan, these two Korad supplies are working very well. No problems and I trust them no problem.

It most likely seems there might be quite some significantly different batches, or even fakes?

[Yansi]

Some local distributor of test equipment.  Don't know where did he got them, and do not care. They were not from Ebay or Aliexpress and probably cost a bit more than you can buy them on ebay, but it is already few years since I have them, so do not remember the price. (I do not trust ebay/china with  regards to buying more expensive and/or heavy parts).

I use the two units on daily basis, even abusing them with inductive loads, making sparks sometimes and they did not fail once. (knock knock). 

I have found a few photos of the power board, from when I have changed the heatsinks to a proper size.

The caps within that unit were Nippon branded, all PCBs are standard FR4. Maybe KORAD makes different versions of the PSU based on the customer requirements, so there might be differences between component selection. Just guessing... I might have only had big luck this time!