Problem power supply Long Wey PS-K3010DF - Page 1
Forum section: electronics / testgear

author: AlCarlos
author_rank: Newbie
timestamp: July 16, 2023, 09:28:43 am
content: Hello everyoneI take advantage of my new subscription to your site to inform you that I have a problem with my 10Ampere Long Wey PS-K3010DF power supplying a LW-K305D-1 motherboard that is similar to the 5 Amp power supply K305D.The problem with my Long Wey PS-K3010DF is that it stays fixed at 11 ampere maximum and turning the non-adjusting pot always stays at 11 ampere.Can anyone help me to solve this problem? I do not even know where to begin with.Thanks to who solves the problem

author: nvmR
author_rank: Regular Contributor
timestamp: July 16, 2023, 10:19:35 am
content: Welcome to the forum. What happens when the load is disconnected?

author: AlCarlos
author_rank: Newbie
timestamp: July 16, 2023, 03:02:32 pm
content: Thanks. The current goes to zero ampere.

author: nvmR
author_rank: Regular Contributor
timestamp: July 17, 2023, 07:02:57 am
content: try to use a simple resistor as a load, and see if it behaves ok. You can cut it off some junk pcb.Try to characterize it under ohms law: I = V/R.See if at some voltage level, your supply starts failing. If not, get some ceramic resistors with a high wattage, and repeat. If all is ok, then your first load is probably a short, or very low resistance.

author: AlCarlos
author_rank: Newbie
timestamp: July 17, 2023, 10:42:47 am
content: Thanks for helping me. I'm going to look for a power resistor and make the suggested measurements.I used a 12V/35W automotive lamp and got the following results:12V - 2.54A6V - 1.74A3V -1.21AWhat do you think?

author: Kean
author_rank: Unknown
timestamp: July 17, 2023, 07:19:25 pm
content: Quote from: AlCarlos on July 17, 2023, 10:42:47 amA 12V 35W globe would draw a bit under 3 amps at 12V, which is what you see. It also translates to approx 4 ohms, so the other measurements also make sense. A globe is not a very precise resistor as it will change value with temperature which will be proportional to the current flowing. But all those readings are in the ballpark.This indicates that the most of power supply readouts are likely working as expected, but it doesn't tell us if the current limiting is working. I would suggest the next step is to see if you can adjust the current limit pot when you have the globe connected and if you can limit the current below those previous readings. Any of those voltage settings would be fine to test, but I'd probably start at 12V.I am not clear on what exactly you are trying to do from your first post. You mention mention two different power supply models, and what you described indicates the output was likely shorted how you had it hooked up.

author: AlCarlos
author_rank: Newbie
timestamp: July 20, 2023, 04:16:58 pm
content: Thank you for your help and attention. I will try to better explain the problem of not adjusting the amperage.

author: AlCarlos
author_rank: Newbie
timestamp: July 20, 2023, 04:29:22 pm
content: The power suplly does not adjust the amperage. It is always set at 11 amps.

author: AlCarlos
author_rank: Newbie
timestamp: July 20, 2023, 04:34:47 pm
content: The manual can be accessed at the link below:https://manuals.plus/m/d0195160cc9df0fdbb378ffe035f3efcccb16d1f10b0372160de306f8c0ef0ce.pdf

author: AlCarlos
author_rank: Newbie
timestamp: July 20, 2023, 04:37:34 pm
content: The power suplly does not adjust the amperage. It is always set at 11 amps.

author: slavoy
author_rank: Regular Contributor
timestamp: July 20, 2023, 05:12:34 pm
content: Start with the simplest things: measure if the potentiometers for current limiting have the correct connections to the PCB. I suspect that this power supply is based on the TL494 controller, and in the datasheet of this IC, you'll find the implementation diagram for the current limiting, so take a closer look there and on the board following the traces from the potentiometers.And I almost forgot - I understand that you are aware of safety precautions when repairing SMPS.

author: nvmR
author_rank: Regular Contributor
timestamp: July 21, 2023, 11:07:47 am
content: Your supply is not stuck at 11A, for the load that you are connecting, the max your supply can output is 11A.Measure your load using a fluke, and see what the resistance is. See that when plugging this into ohms law, for the voltage that you want, the supply cannot supply enough current.