Author Topic: Bench PSU not much current limit adj range after pots replaced  (Read 627 times)

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Offline CirclotronTopic starter

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Bench PSU not much current limit adj range after pots replaced
« on: October 01, 2024, 12:20:03 am »
I've got one of these cheapo noisy bench power supplies that I use for rough-enough-is-good-enough purposes. A while back the voltage setting was becoming unstable, jumping up and down several volts. I read somewhere that they have dodgy pots. As luck would have it, I had a big bag full of exactly suitable 10K pots that work threw out, so I replaced all four and things were back to normal, or so I thought. I was so pleased with myself... Some time later I found that the adjustment range on the current limit setting is not what it should be. Should go from zero to 5 amps, but it only goes from about 4 to 5 amps.

Now I'm *fairly* sure all four original pots were 10K but maybe they weren't. Does anyone have one of these that they could have a look? Or maybe a schematic. Haven't found a schematic on the interwebz. Seems like the same case is used with any number of different internals.
 

Offline FIXITNOW2003

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Re: Bench PSU not much current limit adj range after pots replaced
« Reply #1 on: October 01, 2024, 06:23:27 am »
only circuit i can find on this not all 10K!
 

Offline CirclotronTopic starter

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Re: Bench PSU not much current limit adj range after pots replaced
« Reply #2 on: October 01, 2024, 07:50:20 am »
In the meantime I found the info that put me onto the bad pots, but it seems I didn't look too carefully. The fine adjustment pots are both meant to be 1K. It's weird that the volts setting works okay with one wrong pot but not the current setting.

 

Offline CirclotronTopic starter

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Re: Bench PSU not much current limit adj range after pots replaced
« Reply #3 on: October 01, 2024, 10:50:08 am »
It's weird that the volts setting works okay with one wrong pot but not the current setting.
Just now I set the coarse voltage pot to 20.0V and with the fine pot I could wind it up to 22.9V Could someone try that with their same PSU and see what the figure is?
 

Offline CirclotronTopic starter

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Online J-R

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Re: Bench PSU not much current limit adj range after pots replaced
« Reply #5 on: October 02, 2024, 05:43:46 am »
It's weird that the volts setting works okay with one wrong pot but not the current setting.
Just now I set the coarse voltage pot to 20.0V and with the fine pot I could wind it up to 22.9V Could someone try that with their same PSU and see what the figure is?
I get 22.7V, I think you got it.
 
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Offline CirclotronTopic starter

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Re: Bench PSU not much current limit adj range after pots replaced
« Reply #6 on: October 02, 2024, 10:14:30 am »
I got a pair of 1K pots today. I'll put them in the fine adj positions and see how it goes.
 

Offline CirclotronTopic starter

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Re: Bench PSU not much current limit adj range after pots replaced
« Reply #7 on: October 02, 2024, 10:28:26 am »
Okay, so I pulled it apart and I think I've found the problem...  :palm:
 

Online J-R

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Re: Bench PSU not much current limit adj range after pots replaced
« Reply #8 on: October 02, 2024, 10:58:27 pm »
Okay, so I pulled it apart and I think I've found the problem...  :palm:
Oops, lol
 


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