It's been 3 years since I first bought my bench power supply, a Long wei LW-K3010D. This issue has reoccured to me a couple of months ago, but it usually "went away" when the PSU was switched on for a couple of minutes...

The issue: When I use the voltage knob to adjust the voltage, the voltage goes up and down in a sort of crazy way. Let's say the voltage is 0V and I start turning the knob clock-wise. The voltage suddenly goes 12V, then 9, then maybe 15 and if I leave it for a bit goes down to 2V (for reference: it was supposed to go to 0.1-0.2V)

Could it just be a bad potentiometer?

Does anybody know what the heck has gone wrong so I can replace the part? I would be thankful if someone out there is able to give me some insight! Thanks so much!

  • \$\begingroup\$ How do you measure it? Do you have current limit which might be set to a very low value? \$\endgroup\$ – Eugene Sh. Apr 16 at 13:58
  • 2
    \$\begingroup\$ It is a common fault of regulated, variable DC power supplies. Most likely a cheap, flaky potentiometer that varies the voltage. When the wiper lifts or makes poor connection to the resistive strip, the output voltage goes up. Deadly - a great design would have it fall instead. \$\endgroup\$ – glen_geek Apr 16 at 14:08
  • \$\begingroup\$ @EugeneSh. it is probably a bad potentiometer as it doesn't seem to come from the lack of current.... \$\endgroup\$ – Lefteris Garyfalakis Apr 20 at 0:00
  • \$\begingroup\$ @glen_geek Thank you so much for your detailed explanation of how the potentiometer failed! I have ordered new ones now and will update the thread accordingly. Thanks again! \$\endgroup\$ – Lefteris Garyfalakis Apr 20 at 0:01

Yes, a bad pot could very well be the issue here. I have a similar unit and I find that I got what I paid for which, unfortunately, is not very much. My voltage display drifts over time so that if I set the output for 3.3V the display will drift up by 2-3 volts over time even though the output itself it pretty stable.

I've purchased a higher quality surplus (HP branded) unit that works much better. You might consider the same thing or try replacing some parts to see if you can get better performance from yours.

  • \$\begingroup\$ Alright, thank you soo much! Ordered new pots yesterday and should have them this week. I will update the thread accordingly whether this fixes the issue or not. Yeah I might get a better supply and use the current one only when I need more current. \$\endgroup\$ – Lefteris Garyfalakis Apr 19 at 23:59

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