Products > Test Equipment
Korad KA3005P PSU outputs too low voltage
[Chrille]:
I have a Korad KA3005P bench power supply that I bought a while back but it has never been used to power any high current loads until today when I tried to get it to output 1.5A @ 5V to run a circuit that requires a maximum of about 1.2 amps.
When I powered the device it did not start so I started measuring the voltage on the board and it turned out that the voltage provided by the Korad power supply was only slightly above 4V which is obviously not enough to power the IC’s on the board which require about 5V to run.
I then pulled out a 3.9 Ohm power resistor to simulate a 1.2A load @ 5V and hooked it up to the Korad and it consumed about 1.020A when I had the PSU set to 5V. I used my DMM to check the voltage and it was also about 4.05V which is the same behaviour as when I hooked it up to the PCB I wanted to run in the first place.
I performed measurements on different voltages and this is the result:
Voltage set | Voltage measured
3V | 2.36V (0.59A)
4V | 3.11V (0.785A)
5V | 4.05V (1.020A)
When I hooked it up to a breadboard with a small LED and a resistor it was more or less spot on (4.99V measured instead of the 5.0V set on the PSU) but it only consumed a copuple of milli-amps, which is expected.
Is there a setting I have to enable to get it to output the correct voltage with bigger loads or is my Korad PSU damaged/not working correctly?
ataradov:
There is a calibration mode. I don't remember the details, but it starts with powering up the supply while M4 is pressed. I don't know if that will help with high vs low current consumption.
Kean:
What test leads are you using between the PSU and circuit?
Some of the ones I've received with cheaper equipment would drop close to 1V at 1A, and when examined the cable was only a few strands of CCA.
As the PSU doesn't support remote sensing, you need to use somewhat decent cables.
If the cabling isn't the problem, then there is something wrong with the CC circuit or calibration.
J-R:
I agree, this issue appears to just be expected voltage drop across the leads. If you run the calculations, you'll see they all line up quite well:
2.36V/0.59A=4 Ohms
3.11V/0.785A=3.96 Ohms
4.05V/1.020A=3.97 Ohms
To be sure, run the tests again but check the voltage at the Korad's output posts, not the power resistor. See if the voltage matches what is displayed on the Korad.
Kean:
Yeah, but those calculations just show that the voltage and current measurements mean his 3.9 Ω resistor is probably closer to 4 Ω.
I'd suggest the calculations should be done using current vs voltage drop, not the measured voltage at the resistor, to see how that relates to wire resistance.
3.0 - 2.36 = 0.64 V and 0.64 V / 0.59 A = 1.08 Ω
4.0 - 3.11 = 0.89 V and 0.89 V / 0.785 A = 1.13 Ω
5.0 - 4.05 = 0.95 V and 0.95 V / 1.02 A = 0.93 Ω
So roughly 1 ohm total, or 0.5 ohm in each lead, giving approx one volt drop per amp. That matches what I've seen several times with low quality test leads, typically banana to croc clip.
Of course without the suggested measurements of output directly at the Korad, we don't know the exact voltage drop and I'm just assuming the Korad output is close to the setting.
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