Korad KA3005P power supply faulty/repair

[cavlovic]

I got this power supply a couple of days ago and it worked well until today. I tested it by charging almost empty 72Ah car leadacid battery at 14V 4-5A, under supervision a few times. It worked all well.

Today when I try to do the same thing, once output is turned ON voltage readings are way off of actual voltage. Output on Korad reads 6-7 volts (14V set voltage) and my multimeter reads almost 13V (which is fine as battery is not fully charged).

I also measured current and it reads fine on both Korad and my multimeter. Only voltage reading is way off.

I believe it needs to be calibrated, but not sure how it got so messed up in a few days. I tried to find any information on calibration all day long, but had no luck. I also dissembled the unit but didn't find any obvious pots for adjustments, which led me to believe that it should be done through software or some kind of key combination. Does anyone know how to do this? Manual is all in chinese and I doubt it contains information about calibration.

Also, software which comes with this unit is complete garbage. It's half scrambled and unreadable and it also doesn't function at all. I need to change location to some automatic log location, but I can't seem to be able to do it, so I can only start unit from software but not adjust voltages and current.

Is there any other software that can be used with this Korad KA3005P power supply?

Thank you!

[iloveelectronics]

There was a document posted not too long ago here. Try a search for it.

[Bored@Work]

I believe it needs to be calibrated,

No, it doesn't. It needs to be repaired.

[wraper]

I believe it needs to be calibrated,

No, it doesn't. It needs to be repaired.

+1

[Carrington]

I believe it needs to be calibrated,

No, it doesn't. It needs to be repaired.

+1

[cavlovic]

There was a document posted not too long ago here. Try a search for it.

I know I saw something regarding its' calibration, but just couldn't find it. I also tried google search "site:eevblog.com" and didn't have much luck either. I will keep digging

I believe it needs to be calibrated,

No, it doesn't. It needs to be repaired.

Thank you for the input! I will try to repair it tomorrow and report.

[alm]

Charging a battery without series diode is risky, especially if you turn of the power supply with the battery connected. Many power supplies get really unhappy when they have to sink current. I would expect that to kill the pass transistor or its driving circuit, not the voltage monitoring however.

If this problem suddenly appeared after the battery charging, then I agree with B@W that it's unlikely to be calibration and more likely to be a defect.

[van-c]

I agree that the OP's power supply needs to be sent back for repair.

However, for anyone interested, the following is a calibration procedure I received from SRA Soldering Products.  They obtained it from the manufacturer and the English is a little hard to follow in places, but the procedure does seem to work for calibrating the 0.0V and 30.0V endpoints.  (I didn't try changing the current calibration because on my unit it seemed okay.)  I had to play around with the voltage calibration, though, because getting good agreement at the 0.0V and 30.0V endpoints left the interior points a little inaccurate:

Calibration instrument: benchtop multimeter with 6.5 digits display, 5A electronic load with milliampere display.

Calibration condition: Preheat for 2 minutes after switch on .
Being into calibration mode, press continuously button M4, and switch on at the same time until current and voltage displays blink. At this time, C.V indication is on, which means the power supply is in the mode of zero calibration.
1.      Voltage Zero Calibration: connect the positive pole and negative pole of the multimeter leads into the output terminals respectively. Then, watch the voltmeter and adjust the knob to make the multimeter in the range 0v – 5mv. After that, the zero calibration is over. Press M1 to save the calibration value.
2.      Current Zero Calibration: press the button VOLTAGE/CURRENT, and the current display of the power supply blinks. Connect amperemeter to adjust the current value in the range 0MA – 1MA. Press the button M1 to save the calibration value.
3.      Voltage full-range calibration?adjust voltmeter in the shelf of voltage test. Press M4 and then C.C indication lights on, which means full-range calibration. And then the current display blinks, turn the knob to adjust the voltmeter between 30.01 – 30.02. Press the button M1 to save the calibration value.
4.      Current full-range calibration: press the button VOLTAGE/CURRENT, the current display of the power supply blinks, which means it is in the mode of current calibration. At this time, connect the amperemeter(or electronic load), and then adjust the current value to 5.000A±5MA. After that, press the button M1 to save the calibration value.
5.      Switch off, and then restart the power supply. The calibration ends.

Hope this helps,

--Van

[cavlovic]

Just a small update.

Today I did go through calibration process, and it did help with display voltages, but is still not fixed. I tore the hole unit apart to get a feel of it and did some visual checks. Nothing wrong upon inspection. I will have to dig a lot deeper with my multimeter. Too bad I don't have a scope, as it would help a lot.

Regarding software: do you know any third party software that can be used with this unit? Mine is too scrambled:

This is the version:

[mcinque]

Just a small update. Mine is too scrambled:

Sometimes who write a software use a local charset for the GUI and probably you're missing it. Maybe chinese?

[cavlovic]

Just a small update. Mine is too scrambled:

Sometimes who write a software use a local charset for the GUI and probably you're missing it. Maybe chinese?

Charset should be included with windows, but they maybe programmed it in previous versions and some charcode labels have changed in windows 7, that's why I'm getting those characters. I will install software on windows XP and check if it's the same.

On the other note, I poked a little today through my power supply. They went through trouble of cleaning flux after soldering, but left a mess after cleaning:


I cleaned all boards, and this should be the board, located in front part of PSU, where all the logic is happening:


Current comes to the most right bottom connector from PCB on back of the power supply, where it's been rectified and smoothed, and exits to the front terminals from J2 connector.

I checked all resistors with my mutimeter, and some of them, just up from those 4 caps, read much lower then their written values. Some 1Mohm read 10K, some 10K read 6K etc. Some of them seem fine. I believe those cause the problem with reading proper values, but just want to make sure with more experienced guys before I start desoldering and replacing those.

For input protection there is a 1N5408 diode, 1000v 3A, which would not stop current from car battery when power supply is off. I guess I had it connected before turning output of the power supply ON.


Here is back PCB with rectifier and pass transistors:


Am I onto anything, or way off my path?

Thank you all!

[alm]

Charset should be included with windows, but they maybe programmed it in previous versions and some charcode labels have changed in windows 7, that's why I'm getting those characters. I will install software on windows XP and check if it's the same.

Locale settings may make a difference. It looks like the garbled labels are easy enough to guess, so it should be usable, though ugly. Third-party software is unlikely to support this power supply which is not very popular or emulating an established standard. Your choices are either using whatever crap the manufacturer gives you or writing it yourself, unless another user already did the latter. If their software is written in LABView, then they probably shipped LV drivers. If you own and are skilled in LV, then writing a better GUI would be fairly easy.

I checked all resistors with my mutimeter, and some of them, just up from those 4 caps, read much lower then their written values. Some 1Mohm read 10K, some 10K read 6K etc. Some of them seem fine. I believe those cause the problem with reading proper values, but just want to make sure with more experienced guys before I start desoldering and replacing those.

Most likely other resistors in parallel. A 1 Mohm resistor is unlikely to go down in resistance to exactly 10 kohm. If you want to be sure, desolder and measure its resistance. I would rather figure out the circuit and measure voltages. Presumably a resistive voltage divider (possibly switchable if it has multiple ranges, those 74HC part might be analog switches), possibly a buffer amplifier (one of those SO-8 packages?) and then an ADC (probably built into that MCU with its part number sanded off). Ideally you would have values from a known good power supply to compare. I would be more suspicious of active devices, since resistors are less likely to be damaged by minor overloads.

For input protection there is a 1N5408 diode, 1000v 3A, which would not stop current from car battery when power supply is off. I guess I had it connected before turning output of the power supply ON.

That's most likely an anti-parallel diode across the input, that does not protect against current flowing from the battery to the power supply. I was talking about a series diode between power supply and battery.

[mcinque]

Charset should be included with windows

Afaik, european, u.s. or australian Windows does not have asians charsets installed by default. Maybe I'm wrong.

Locale settings may make a difference.

I agree.

[alm]

I think there was another piece of crappy software from one of the Chinese test equipment manufacturers (Owon? Hantek? Rigol?) that had a similar issue.

Edit: this may have been the post I was thinking about.

[mos6502]

Is there another PCB in there with opamps? Because it doesn't look like there's analog regulation circuits on there.

Could it be that the KA3005 uses the microcontroller to do the actual regulation?

I looked at the Korad website, and the specs say that the transient response is 100ms. Yes, milliseconds! That's around 1000 times slower than a proper linear supply. Unless that's an error, that would indeed mean that the micro does the actual regulation. Which would be insane, and horrible, and make this supply all but useless except maybe for battery charging.

I watched Dave's review and the steps in the voltage response would also point towards that.

Anyone have a schematic for this piece of ... kit?

[alm]

How about U5-U7 (top right in the second picture)? Can't read the markings, but they look like they might be op-amps to me. Three dual op-amps is plenty for a linear bench supply with an analog regulation loop.

[mos6502]

Right. But they could also be level shifters/buffers for the R2R DAC. IMHO the 100ms transient response (no opamp is THAT slow) and the steps in the voltage after turn-on (watch Dave's video) speak a clear language.

Unfortunately Dave didn't do a transient test. Anyone who owns one of these want to do one? All you need to do is to connect a big resistor to the output and switch it with a MOSFET at ~100 Hz and trace the output voltage on a scope.

I'd love to see a schematic for this thing. These are the cheapest 30V/5A PSUs out there. You can get a KA3005D for 65 Eurobucks here in Germany. But it looks like you'd have to do some major hacking and add your own regulation circuit.

[alm]

I agree with you about the slow transient response, suspicious turn-on behavior and that putting an MCU in the regulation loop would be a bad idea, but without a schematic or someone reverse-engineering the design there is no way to be certain. The slow transient response could also be a really over damped loop response (at least it won't oscillate), for example.

[Electro Fan]

Anyone who owns one of these want to do one? All you need to do is to connect a big resistor to the output and switch it with a MOSFET at ~100 Hz and trace the output voltage on a scope.

+1 on this request/suggestion

[cavlovic]

Is there another PCB in there with opamps? Because it doesn't look like there's analog regulation circuits on there.

Could it be that the KA3005 uses the microcontroller to do the actual regulation?

I looked at the Korad website, and the specs say that the transient response is 100ms. Yes, milliseconds! That's around 1000 times slower than a proper linear supply. Unless that's an error, that would indeed mean that the micro does the actual regulation. Which would be insane, and horrible, and make this supply all but useless except maybe for battery charging.

I watched Dave's review and the steps in the voltage response would also point towards that.

Anyone have a schematic for this piece of ... kit?

Nope, this is the only board with opamps. I would also like to know if anyone has schematics for this power supply. I couldn't find it anywhere.

Once again, the board:


Parts:
U5-U7: dual opamps TL082C:


U12: darlington transistor array ULN2003A:


U13: ATMEL364:look previous at picture with your head or monitor upside down  .

When unit is powered on and my LED lighting pulling 1.4amps at 12V (12V set to power supply), voltage reading jumps around at the unit, but multimeter shows exactly 12v. Current readings on the power supply are fine.

When I put my finger on R10-R17 (right above 4 caps in first picture) and thus heating them up and increasing resistance, voltage drops on power supply, with it the current. From 12V and 1.4amps I managed to bring it down to 11V and sub 1amp. This may tell you a little more about regulation loop.

Any further help is very much appreciated.

Thank you all,
Balsa

[alm]

Like I said, I would trace the voltage measurement connections and go from there. There are likely thin traces coming from J2 (or the input header) going via some resistors to U10. See if there are any active components on this path, check resistors and check if the U10 input gets a stable DC voltage (probably varying between 0-5 V or so, scaling linearly with the output signal).

The fact that voltage regulation appears to be independent of voltage measurement argues against the MCU in the regulation loop in my opinion. Why would you waste two ADC inputs on sensing the output voltage?

[cavlovic]

Like I said, I would trace the voltage measurement connections and go from there. There are likely thin traces coming from J2 (or the input header) going via some resistors to U10. See if there are any active components on this path, check resistors and check if the U10 input gets a stable DC voltage (probably varying between 0-5 V or so, scaling linearly with the output signal).

The fact that voltage regulation appears to be independent of voltage measurement argues against the MCU in the regulation loop in my opinion. Why would you waste two ADC inputs on sensing the output voltage?

I did listen to your advice and traced J2 to U10, through a couple of resistors and caps, but there are no active components in the path.

Then I spent 4 additional hours trying to figure out what is wrong (it was PITA to measure while unit is powered on since there is very little space, even though I have a set of really thin probes), and I may be onto something (my 4 hours equate to maybe a couple of minutes to some of you here, so please bare with me ).

Voltage set and detection part:
Both outputs of U5 opamp are used for voltage regulation and display. Output 1 (PIN 1) goes from 0.04v (0v set output voltage) to 2.84v (31v set output voltage) and this output is only dependent of set voltage, regardless of load. Output 2 of U5 reads 0.7V to 1.16V, also jumping all over the place, and this opamp output is dependent of the load, and this should be the one that causes voltage reading problems. Output 2 of U6 also reads 0.04v to 2.84v and this one is not dependent of the load attached.

Current set and detection part:
Output 1 of the U6 reads 0.04v (0amps set current) to 2.56v (5.1amps set current). Same goes for output 1 of the U7. Both of them are not dependent of the load and represent just set current values. Output 2 of U7 reads -3v to 2.71v and this one is load dependent and probably is used for displaying actual current flow. This reading started acting up today also, so both voltage and current readings are off, even though they are spot on to set values.

I believe that both output for voltage and current when load is present should read almost identical to their set values (0.04v-2.84v for voltage and 0.04v-2.56v for current) if opamps didn't fail.

I guess those opamps need replacement, and they are causing  all the trouble. I also may be off my path here, so any input is much appreciated.

Also, if anyone happens to have Korad KA3005P or D laying around, measuring output 2 (PIN 7) of both U5 and U7 under load, from minimum to maximum voltage and current would help me a lot.

Thank you all,
Balsa

[KORAD TECHNOLOGY]

I got this power supply a couple of days ago and it worked well until today. I tested it by charging almost empty 72Ah car leadacid battery at 14V 4-5A, under supervision a few times. It worked all well.

Today when I try to do the same thing, once output is turned ON voltage readings are way off of actual voltage. Output on Korad reads 6-7 volts (14V set voltage) and my multimeter reads almost 13V (which is fine as battery is not fully charged).

I also measured current and it reads fine on both Korad and my multimeter. Only voltage reading is way off.

I believe it needs to be calibrated, but not sure how it got so messed up in a few days. I tried to find any information on calibration all day long, but had no luck. I also dissembled the unit but didn't find any obvious pots for adjustments, which led me to believe that it should be done through software or some kind of key combination. Does anyone know how to do this? Manual is all in chinese and I doubt it contains information about calibration.

Also, software which comes with this unit is complete garbage. It's half scrambled and unreadable and it also doesn't function at all. I need to change location to some automatic log location, but I can't seem to be able to do it, so I can only start unit from software but not adjust voltages and current.

Is there any other software that can be used with this Korad KA3005P power supply?

Thank you!

This is Krissy from KORAD TECHNOLOGY. Would you please kindly send me your e-mail address? I want to solve it soonest. Thank you in advance!

[cavlovic]

I got this power supply a couple of days ago and it worked well until today. I tested it by charging almost empty 72Ah car leadacid battery at 14V 4-5A, under supervision a few times. It worked all well.

Today when I try to do the same thing, once output is turned ON voltage readings are way off of actual voltage. Output on Korad reads 6-7 volts (14V set voltage) and my multimeter reads almost 13V (which is fine as battery is not fully charged).

I also measured current and it reads fine on both Korad and my multimeter. Only voltage reading is way off.

I believe it needs to be calibrated, but not sure how it got so messed up in a few days. I tried to find any information on calibration all day long, but had no luck. I also dissembled the unit but didn't find any obvious pots for adjustments, which led me to believe that it should be done through software or some kind of key combination. Does anyone know how to do this? Manual is all in chinese and I doubt it contains information about calibration.

Also, software which comes with this unit is complete garbage. It's half scrambled and unreadable and it also doesn't function at all. I need to change location to some automatic log location, but I can't seem to be able to do it, so I can only start unit from software but not adjust voltages and current.

Is there any other software that can be used with this Korad KA3005P power supply?

Thank you!

This is Krissy from KORAD TECHNOLOGY. Would you please kindly send me your e-mail address? I want to solve it soonest. Thank you in advance!

PM sent.

[mos6502]

This is Krissy from KORAD TECHNOLOGY. Would you please kindly send me your e-mail address? I want to solve it soonest. Thank you in advance!

What is your policy regarding schematics? Can you give them out or not?