Workbench DC Power Supply Project.....sounds feasible?

[partyanimallighting]

Hi all, I'm posting in the hope that a wise one will point out any unseen errors. I have two honeycomb power supplies (12V 20A and 24V 10A) mounted under my work desk and I connect to them via two XLR's mounted to the front of the desk with loose wires for connection for testing. I'm thinking of buying a DIY project box and installing the two power supplies in this, along with a fan, voltmeters and chassis mount banana plugs out for each voltage. I was thinking about also including a DC to DC converter (fed off the 24V power supply), also to a voltmeter, banana plugs and a rotary potentiometer, to get a higher voltage feed for testing COB diodes and such, along with units that need higher operating voltages (36V ~ 48V). I don't see any issues with this project but I thought it best to post here in case someone sees a potential fire hazard in the making. If I'm given the all clear, the only issue I will have would be to remove the small blue SMD pot mounted to the DC to DC converter to wire in a rotary pot and what value rotary pot to use for the front panel adjustment. Any and all advice will be gratefully accepted.

 

 

[boatman]

If it helps the small blue pot in the second picture is marked "503" which means it is 50k.

[themadhippy]

might want to include an ammeter ,not essential but useful to see if that burning smell is the circuit under test or just your soldering iron being in the wrong place

[partyanimallighting]

Soooo, boatman, I'm looking for a 3 pin 50k rotary pot which will be wired directly to the three points where the 3296W is soldered onto the PCB, correct? Something like this?

https://www.amazon.com/TWTADE-Potentiometer-Single-Variable-Aluminum/dp/B07GB4WSS3/ref=sr_1_4?crid=MSCYDSD6VC3D&keywords=50k%2Bpotentiometer&qid=1686586951&sprefix=50k%2Bpote%2Caps%2C1227&sr=8-4&th=1

If I use something like this, will there be a limit as to the amount of voltage that passes through it? These little DC to DC converters are rated at maximum 60V and I successfully tested a COB diode tonight with a 24VDC feed into the converter and I got the voltage up to around +-45V and the COB lit up quite nicely but I'm concerned about overload.

I actually thought that this COB was blown and didn't know how to test it and did not want to put 24V into it but YouTube came to the rescue. I had bought a few of these converters a while back and tested a couple but they never worked so I just tossed them in a drawer but I had to find a way to test the COB so I found a working converter out of the pile and I realize now that I'll need that adjustable voltage feature for future testing, hence this post to confirm I'm on the right path with this build.

themadhippy, I am considering ammeters for each output but that depends on if I have the space on the front panel (and I already bought some tiny voltmeters). I don't to buy too big a case that'll take up a lot of space and a horizontal case will be better for spacing out the 3 planned outputs. As for the soldering iron, once it's not burning my flesh......

Here are a couple pictures of the actual pot on the PCB for reference.

 

 

[indyld]

It will no doubt puts volts on the bench and maybe use up some parts lying around. I did something similar with an old ATX PSU quite a while go. 

Thing is, speaking as someone that uses a bench DC power supply every day, you may soon wish you had more functionality and the time spent / parts used don't make up for the lack of such. I use my DC supply for diagnosis much more than just to power something up and this is where the little bit of extra function come in: ammeter, constant voltage, constant current etc. 

My most used voltages are probably 1v, followed by 20v. The former for injection, but I regularly need 3.3, 5, 12, 20v at a range of current limits.

As you seem to have a requirement to repair kit, and are developing confidence in techniques, you might ask if you just need an adjustable, limited, bench DC PSU and skip the DIY stage.

Edited June 13, 2023 by indyld

[sunray]

15 minutes ago, indyld said:

It will no doubt puts volts on the bench and maybe use up some parts lying around. I did something similar with an old ATX PSU quite a while go. 

Thing is, speaking as someone that uses a bench DC power supply every day, you may soon wish you had more functionality and the time spent / parts used don't make up for the lack of such. I use my DC supply for diagnosis much more than just to power something up and this is where the little bit of extra function come in: ammeter, constant voltage, constant current etc. 

My most used voltages are probably 1v, followed by 20v. The former for injection, but I regularly need 3.3, 5, 12, 20v at a range of current limits.

As you seem to have a requirement to repair kit, and are developing confidence in techniques, you might ask if you just need an adjustable, limited, bench DC PSU and skip the DIY stage.

I was thinking along the same lines too, however the vast majority of my bench work is at 12-13.8V or breadboarding which have built in variable psu's.

In my situation the 0-30V PSU tends to be a secondary choice.

 

My hunch here is the enclosure pictured may be approaching half the cost of a variable PSU and therefore not the most appropriate route to go down.

[DrV]

Another vote for a variable current limited supply. I've got a pair of 0-60V 1A supplies which I can connect as a tracking +/- pair (for audio stuff) or use individually and they rank in importance with the 'scope as essential items of test kit. Keep the supplies you already have for second stage testing (once you think you've sorted the initial problems) and invest in a proper bench unit with current limiting for initial powering up of a faulty item. They're not that expensive and are an incredibly useful diagnostic tool.

[partyanimallighting]

Well all things considered, I do have lots of old (new unused) stuff lying around such as maybe 20 or 30 honeycomb 12 and 24V PSU's, I checked and the meters I bought are amps and volts so that's another plus. I also have power switches, chassis mount banana plugs in a variety of colors, fans etc. The only things that I really have to buy actually is the DIY case (sunray, I can pick one of the up for around $18.00) and the 50K pot (thanks boatman) hence my interest in pursuing this little project (it'll cost me nothing really) and I know when my OCD kicks in it'll look like a came out of a factory (a Chinese factory that is). My main dabble areas as some of you who have helped me with problems before would know, are LED PAR's and other LED based fixtures so it's basically 12V and 24V, sometimes 28V but rare. The first time I ever tested a high power 300W LED COB was earlier this week and I used the Buck converter to drive it and that's when I saw the need for the variable voltage output. Apart from the PAR's, I'll find myself fiddling around with LED moving heads and the PSU's are the normal issue with these and again, it'll be 12V or 24V, maybe 36V. And then there are my 5R's and 15R's but I've been warned here about messing around with those 380V PSU's and I was told to stay away from attempting to repair them. Just replace them. I understand the advice to buy one but I think I would have a lot of fun building this and, as I gain some experience with my repairs, I will definitely buy a proper supply and downgrade my DIY project to secondary bench PSU status. Can I get an amen?

Edited June 15, 2023 by partyanimallighting

[sunray]

5 hours ago, partyanimallighting said:

Well all things considered, I do have lots of old (new unused) stuff lying around such as maybe 20 or 30 honeycomb 12 and 24V PSU's, I checked and the meters I bought are amps and volts so that's another plus. I also have power switches, chassis mount banana plugs in a variety of colors, fans etc. The only things that I really have to buy actually is the DIY case (sunray, I can pick one of the up for around $18.00) and the 50K pot (thanks boatman) hence my interest in pursuing this little project (it'll cost me nothing really) and I know when my OCD kicks in it'll look like a came out of a factory (a Chinese factory that is). My main dabble areas as some of you who have helped me with problems before would know, are LED PAR's and other LED based fixtures so it's basically 12V and 24V, sometimes 28V but rare. The first time I ever tested a high power 300W LED COB was earlier this week and I used the Buck converter to drive it and that's when I saw the need for the variable voltage output. Apart from the PAR's, I'll find myself fiddling around with LED moving heads and the PSU's are the normal issue with these and again, it'll be 12V or 24V, maybe 36V. And then there are my 5R's and 15R's but I've been warned here about messing around with those 380V PSU's and I was told to stay away from attempting to repair them. Just replace them. I understand the advice to buy one but I think I would have a lot of fun building this and, as I gain some experience with my repairs, I will definitely buy a proper supply and downgrade my DIY project to secondary bench PSU status. Can I get an amen?

Amen.

 

I've always been a dabbler / constructor and I have loads of old junk laying around "in case it comes in handy" for my projects I wish to do but know will never get done. One thing I learnt way back was the basic parts are dirt cheap but then the enclosure, sockets, knobs etc were always the killer. Hence my comment about the price of enclosure.

[partyanimallighting]

What is it? Why can't we throw out stuff? A couple of weeks ago I found an Elation Opto-Branch 4 DMX splitter in storage. Completely cannibalized and gutted out. Toss it? Noooo!! I took it apart, replaced all the missing encapsulated transformers, put in IC sockets and re-seated 8 75176's, 4 LM339's and 1 HD74HC04P which had failed and was the cause of the unit being tossed in a crate in the first place. I even replaced the power cord with a True Con. Powered up and boom!! No, not an explosion. A fully functional unit rescued and ready to serve again after being packed away since 2010 based on the date on the original picture. Total cost? About US35.00 😁 This is the same reason I'm working on those Acclaim X-Power PRO's in another post. Recycle. Recycle. Recycle.

Edited June 15, 2023 by partyanimallighting

[themadhippy]

Quote

and the 50K pot

personal choice,but I'd recommend a multiturn pot,you'll swear at it when you need to go to from the extremes of the range,but swear by it when your trying to dial in  an exact voltage.

[alistermorton]

Or a coarse/fine drive, as used to be popular on communication receivers?

[sunray]

6 hours ago, alistermorton said:

Or a coarse/fine drive, as used to be popular on communication receivers?

As on my 0-30V PSU, I much prefer this option.

[partyanimallighting]

Is this type of pot readily available online? Is it that this particular pot does not have a stop but continuous rotation? Similar to the 3296 mini pot on the buck DC to DC converter? Did some searches and I'm seeing linear taper pots and I'm thinking that's what I'm looking for. Please excuse my lack of knowledge. Remember I'm the new guy.

 

[themadhippy]

31 minutes ago, partyanimallighting said:

Is this type of pot readily available online?

if you mean multiturn then yea,useless me posting links as they'll be uk centric,but a search for

3590S Precision Wirewound Potentiometer

should get you close

 

Quote

Is it that this particular pot does not have a stop but continuous rotation

no ,they have stops, but it takes 10  rotations of the knob for full travel

Quote

linear taper pots and I'm thinking that's what I'm looking for

yep that be the type