30V/5A DC Power Supply having issues

Thread Starter

Lumenosity

Joined Mar 1, 2017
461
Hello,

About 2 years ago I purchased this 30V/5A DC Power Supply and for most of that time it's done a great job. Lately, however, it seems to be having more and more problems.

It is becoming very difficult to set it to a specific voltage
It seems to have lost it's ability to be set to most any voltage, but especially lower voltages under 5v for example.

I'm wondering if there's any "common" components in these inexpensive Power Supplies that I might be able to change to remedy this.

Alternatively, I could open it and see what's inside.
I was hoping some of you guys may have one of these and might be familiar with it.

any suggestions appreciated.



Here's a picture of the POTS.
There are no marking on the POTS other than the letters WL
 
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AlbertHall

Joined Jun 4, 2014
8,187
It is becoming very difficult to set it to a specific voltage
It seems to have lost it's ability to be set to most any voltage, but especially lower voltages under 5v for example.
Do you mean it won't go below 5V or does the voltage leap around when you try to adjust it?
In the latter case the problem is likely to be the voltage control pot itself and you may be able to some switch cleaner into it - though many are too well sealed for that. Otherwise it shouldn't be too difficult to replace the control.
 

dendad

Joined Feb 20, 2016
2,935
I have one of those and the problem I had was a crook relay. That is probably not your problem. It is more likely a faulty pot or a dry joint.
 

Thread Starter

Lumenosity

Joined Mar 1, 2017
461
Do you mean it won't go below 5V or does the voltage leap around when you try to adjust it?
In the latter case the problem is likely to be the voltage control pot itself and you may be able to some switch cleaner into it - though many are too well sealed for that. Otherwise it shouldn't be too difficult to replace the control.
Thanks. I'll probably give this a shot.

I can barely set it to any voltage I want. Sometimes when I adjust the knob it does nothing at first....and will suddenly jump to 35v (maximum setting) as I rotate it.

That leads me to believe it could actually be the POT.

If anyone else has had this issue and replaced the POT and could tell me the specs on a replacement would be great. Otherwise I'll just assume I need a POT with a range of 0 to 35v and at least 6A rating?

If it's defective, I wonder how I can determine the OHMs rating (if it's not printed on it somewhere)?
 

MrChips

Joined Oct 2, 2009
19,159
First thing to try is to clean the pot with control cleaner spray or iso-propyl alcohol.

Edit: btw, you do not need a 35V 6A pot. The pot does not pass 6A. It is a low voltage, low current control that is fed to the power controller circuitry.
 

AlbertHall

Joined Jun 4, 2014
8,187
I wonder how I can determine the OHMs rating (if it's not printed on it somewhere)?
If you have a multimeter you can measure it (once it's disconnected from the rest of the circuit) between the two outer connections. The problem is with the centre terminal.

But do try getting some cleaner into it first.
 

Thread Starter

Lumenosity

Joined Mar 1, 2017
461
If you have a multimeter you can measure it (once it's disconnected from the rest of the circuit) between the two outer connections. The problem is with the centre terminal.
But do try getting some cleaner into it first.
Maybe a dumb question but.....

If the POT is defective or burned out etc....would I still be able to accurately get the correct OHMS that way?
If not, is there a secondary way to discover the OHMS of a POT that is not marked?
 

MrChips

Joined Oct 2, 2009
19,159
There are four pots, two for fine setting and two for course setting.
Fine control pot is 1kΩ linear.
Course control pot is 10kΩ linear.

Watch the diameter of the pots. They are 15mm diameter.
 

Thread Starter

Lumenosity

Joined Mar 1, 2017
461
At the bottom of the unit are three receptacles for leads. Red one is Positive, Black one is ground and Yellow one is also ground ?

All three are screw in pieces that can be twisted to unscrew (and remove).

QUESTION:
What would be the result if they were not tight? it seems if they are loose, there may not be a good connection going from the leads to the unit.
I found out that all three where not a as sung tight as they could have been.. I tightened them and the problem (so far) seems to have gone away.

Maybe that was all it was? I didn't know those knobs were able to turn so I hadn't checked them.
 

dendad

Joined Feb 20, 2016
2,935
At the bottom of the unit are three receptacles for leads. Red one is Positive, Black one is ground and Yellow one is also ground ?
The red is positive as you say but the black is not ground but the negative terminal. It can be ground if you connect the black and yellow together, but so can the positive if you connect the red and yellow together.
The power supply output is floating, not connected to ground unless you do so.
If you can measure a connection between the black and yellow without you putting a wire there, then there is a fault.

But it does sound like you may have found the problem :)
 

MrChips

Joined Oct 2, 2009
19,159
At the bottom of the unit are three receptacles for leads. Red one is Positive, Black one is ground and Yellow one is also ground ?

All three are screw in pieces that can be twisted to unscrew (and remove).

QUESTION:
What would be the result if they were not tight? it seems if they are loose, there may not be a good connection going from the leads to the unit.
I found out that all three where not a as sung tight as they could have been.. I tightened them and the problem (so far) seems to have gone away.

Maybe that was all it was? I didn't know those knobs were able to turn so I hadn't checked them.
Those connectors are called "banana jacks" or "binding posts".



How did you connect to these posts? Did you plug in mating "banana plugs"?
You tighten the "knobs" only if you are wrapping conductive wire around the knob or inserting bare conductive wire in the tiny hole in the metal post.
If you used banana plugs a loose "knob" would not cause your problem.

BTW, your power comes from the two outer posts, not from the center post. BLACK is not ground. Your power supply is a "floating" power supply. If you don't know what this means, don't be afraid to ask.

The center post is safety ground.
 

MisterBill2

Joined Jan 23, 2018
3,721
Any part of the supply that becomes a loose connection can cause all sorts of problems. Those potentiometers (pots) are notorious for developing an unstable connection with the slider portion.Often cleaning will restore their functionality for a while. If one of the output terminal connections has become loose that will also cause erratic output voltage jumps. I have a similar looking power supply, 0-50 volts and 0-50 amps. It was claimed to be defective and so I purchased it very cheap. The "defect" is that the voltage limit and current limit adjustments must be set above zero, as well as the over voltage limiter. So there it was just a case of knowing how the thing worked that got it to a usable point. It also has the cheap pots, I have not yet needed to replace them,but for a lab type instrument would use better quality devices, even though it would mean changing all of the connections from the pots to the control assembly
 

John_2016

Joined Nov 23, 2016
55
Since it's a cheap power supply, does it make sense to briefly assess how much time do you really want to go on with the repair, that
from the photo supplied there has already been some components resoldered, and buty a new power supply?
 

MisterBill2

Joined Jan 23, 2018
3,721
Since it's a cheap power supply, does it make sense to briefly assess how much time do you really want to go on with the repair, that
from the photo supplied there has already been some components resoldered, and buty a new power supply?
The "cheap" power supply of mine, which looks similar to that one, but much bigger, runs $600 on discount sellers websites. So cheap may be a very relative term. Much less than an HP supply of equal ratings from back when HP sold test equipment, for sure, though.
 

Thread Starter

Lumenosity

Joined Mar 1, 2017
461
When tightened, the problems remain.
I would say the FINE adjustments don't really seem to do anything and never have as best I can recall.

I have a situation where I'm trying to apply low current (1 Amp) and 16v DC to an automotive battery.
I find this impossible. I have to set the current to roughly 4 amps to get a voltage of 16 volts.

Even then, it dances around and will drop to zero, then spring back up...it's all over the place.
Are these symptoms still likely the pots? Should I be able to set the current at 1 amp and the voltage at 16v? Or is it all dependent on the battery?
 
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Thread Starter

Lumenosity

Joined Mar 1, 2017
461
Results of testing the pots....apparently I do have several bad pots. Replacements ordered.

POT 4 Fine (Current)
End terminals - 950 ohms, center to end terminals - erratic until cleaned (good on one side only after cleaning)

POT 3 Coarse (Current)
End terminals - 11k ohms, center to end - erratic until cleaned (good after cleaning)

POT 2 Fine (Voltage)
End terminals - Open (infinity), center to end terminals - Infinity

POT 1 Coarse (Voltage)
End terminals 10.00k ohms, center to end terminals - erratic until cleaned (good after cleaning)
 
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MisterBill2

Joined Jan 23, 2018
3,721
The symptoms were pointing in that direction, so it made sense to check hem. I also suggest looking at the solder connections as well. Back a few years, quite a few, actually, Radio Shack had a lot of failed solder connections in some of their products. So it can happen there as well.
 

AlbertHall

Joined Jun 4, 2014
8,187
Should I be able to set the current at 1 amp and the voltage at 16v? Or is it all dependent on the battery?
It is dependent on the battery or whatever load is connected to the supply.
The power supply can set either the voltage or the current but not both at the same time.

Car batteries shouldn't normally be able to get to 16V. The maximum charging voltage should be 14.2V to 14.8V.
 

Thread Starter

Lumenosity

Joined Mar 1, 2017
461
It is dependent on the battery or whatever load is connected to the supply.
The power supply can set either the voltage or the current but not both at the same time.

Car batteries shouldn't normally be able to get to 16V. The maximum charging voltage should be 14.2V to 14.8V.
Agreed. However, that higher voltage was intended only for a two hour period for desulfating. And is why I wanted low current. (I know, I'm opening a can of worms)
The battery was new, but I inadvertatnly let it slowly self-discharge to 11.6 volts and it may have been below 12v (but above 11.6v) for several months

Is there a way to apply a 16v @ 1 amp charge to a 12v 6AH battery?
 

AlbertHall

Joined Jun 4, 2014
8,187
Is there a way to apply a 16v @ 1 amp charge to a 12v 6AH battery?
You can apply 1A and the battery will decide what voltage that produces across its terminals.
You can apply 16V across the battery and the battery will decide how much current that drives through it.
 
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