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Variable Voltage Power Supply Problem


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Hi all, I posted on this topic before and I think the post got lost in the flow of other posts by different forum users. In my original post I mentioned that I was building a bench-top power supply with 12VDC, 24VDC and a variable voltage output from 24VDC up to about 48VDC. I partially completed the unit but I was stumped on the variable voltage output. I used a 12VDC and a 24VDC power supply and my plan was to use the 24VDC output to power a DC to DC buck converter with a pot attached to get the voltage variations. I tested the buck converter off the 24VDC PSU and I got the voltage adjustments I required off the 3296 pot on the converter but when I connected an external 50K pot I got no adjustment and I ended up frying the buck converters that I had. I tried different wire orientations but no positive result and I wired leads directly to where the pins 1, 2 and 3 for the 3296 were removed to the external pot. The power supply works fine, I have my 12 and 24VDC outputs but there's a gaping hole in the front panel where my variable voltage meter is supposed to fit and a hole below this for the pot to adjust voltage on that output. I've searched on Amazon and AliExpress (I'm in the West Indies so this is the best source for me) but I can't find a suitable DC to DC step up voltage regulator with an external pot. The only thing I've found that I think may work are DC motor speed controllers but I'm looking for some guidance here once again. Please excuse my craftsmanship in the pictures below as I did not have a nibbling tool and I used a rotary tool to cut the meter knockouts.



2023.09.01 Power Supply 001.jpg

2023.09.01 Power Supply 002.jpg

2023.09.01 Power supply 004.jpg

2023.09.01 Power supply 006.jpg

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Here are the images of the buck converters I intended to use, the 3296 pot that was removed and the 50K pot that was tested. As you can see, I simply removed the 3296 and installed a Molex connector with a harness for the 50K pot but that never worked. The harness is obviously necessary for mounting on the front panel. I mean, there's a hole there already, right?

3296W Trimming Potentiometer 001.jpg




DC to DC Buck Converter 002.jpg

DC to DC Buck Converter MOD. 006.jpg

DC to DC Buck Converter MOD. 007.jpg

Edited by partyanimallighting
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These are the motor controllers I am seeing on AliExpress and Amazon but I'm not sure that they will work for the purpose I intend to use them for. They do have the external pot that I require and these pots seem to be wired in exactly the same way that my external pot was wired but my wiring did not work. I really hope someone will steer me in the right direction so I can finally finish this little project.


AliExpress DC Motor Controller 001.jpg

AliExpress DC Motor Controller 002.jpg

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How about this: https://www.aliexpress.com/item/32840324731.html

0-50V variable output at 5A, and it’ll take anything from 6V up to 50V as its input voltage (so your could feed it from your 24V rail, for example. 
You’d have to double check the dimensions, but it’s approximately right for the size hole you have in that front panel already. 

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Thanks Tom Baldwin. I did see this during my searches but because I already had an available voltmeter and the voltmeter hole was already cut out and the hole drilled for the pot on the front panel I didn't consider this type. Space would be the other issue as I will have to fit the module itself inside the project case and this display is larger but I can cut the display knockout on the front panel larger. I had originally drilled holes on the back panel to mount the other buck converter (which is a lot smaller) so I'll have to see if I have enough depth from the inside of the back panel to the edge of the two mounted power supplies. Aesthetically, the original planned small buck booster connected to a similar sized voltmeter would have been perfect but if that's not possible...... If I can't get the mounting space, the search will continue. I'd love to get some feedback also as to what I could have done wrong with my initial conversion from the 3296 to the 50K external pot.

2023.09.01 Power supply 008.jpg

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