Korad KA3005P PSU outputs too low voltage - Page 1
Forum section: electronics / testgear

author: [Chrille]
author_rank: Contributor
timestamp: December 18, 2024, 09:44:15 pm
content: 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 measured3V | 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?

author: ataradov
author_rank: Super Contributor
timestamp: December 18, 2024, 11:07:28 pm
content: 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.

author: Kean
author_rank: Unknown
timestamp: December 19, 2024, 02:36:21 am
content: 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.

author: J-R
author_rank: Super Contributor
timestamp: December 19, 2024, 05:46:29 am
content: 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 Ohms3.11V/0.785A=3.96 Ohms4.05V/1.020A=3.97 OhmsTo 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.

author: Kean
author_rank: Unknown
timestamp: December 19, 2024, 06:08:57 am
content: 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 Ω4.0 - 3.11 = 0.89 V and 0.89 V / 0.785 A = 1.13 Ω5.0 - 4.05 = 0.95 V and 0.95 V / 1.02 A = 0.93 ΩSo 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.

author: J-R
author_rank: Super Contributor
timestamp: December 19, 2024, 08:35:03 am
content: Ah yes, I like that math much better. Not sure what I was trying to show with mine.

author: [Chrille]
author_rank: Contributor
timestamp: December 21, 2024, 08:41:42 pm
content: I tried another set of cables yesterday. This time I used my fluke test leads with attached alligator clips and they worked a lot better. I got about 4.85V at the load when the power supply was set to output 5.00V and 4.95V when the PSU was set at 5.1V output and the test load consumed about 1.24A if I remember correctly so it looks like the power supply works as expected when using better quality leads.Thanks for your input and suggestions!