Electronics Test Bench PS

I would like to build a regulated test bench PSU w/meters ect. to test all the neat circuits that I have learned from this site. I have found schematics on many sites on the web, but I would be building a bunch of circuits with nothing to test them with. So I was wondering if a computer PSU could be modified to suit my needs. If so, does anyone know of any docs or guides that would help me? Would it be too hard to mod the PSU for variable voltage? I have a nice little ATX 250w PSU from a dead Dell that I can use…Liton PS-5231-1.

Thank you in advance for any help on this…

 

eBay

I just bought one off eBay.
Mine's a little 50W one I think. It's got an on/off switch and a couple of standard PC power molexs. Just the job. It cos £5.
Have a trawl through eBay.

 

you could do it with a computer psu but they have fairly noisy lines, may be better getting a regulated wall wart then adding the bits u want such as meters

 

I wouldn't think that the walmart transformer would be much better than the PSU, probably have a nice 60 (or 50) hz humm.

 

a regulated wall wart should be just fine spesh if you get a linear one.

col

 

I was looking for something a little more versatile, something I could use for testing circuits also. Ever since I started my computer mod, I have taken a keen interest in electronics. I’m even contemplating taking a course or two in basic electronics. So I’ve come to the conclusion that a test bench is in order. I found an oscilloscope program that utilizes the Mic. In port on a sound card (probably OK for a beginner like me), but it be nice to turn the testing power supply into a project. I did a bit-tech search but I could not find anything relating to what I would like to do.
It just seems like such a logical thing to do…Looking at the PSU circuit board I see labels for -12V, -5V, +12V, +5V, PowerOn and Gnd plus a couple of other wires (+5V-S, +5VFP, TFSC & PG) I do not know. The mains plug is filtered and there is a thermistor attached to the main heat sink for thermal protection (good guess?). It seems most of the test bench requirements are there. I just need to find out how to break out a circuit for the variable voltage and where to attach Volt & Amp meters and after reading dfhaii & ConKbot of Doom’s comments, a way to stabilize the power.

I know that buying one would be easier but what lessons would I learn by doing that, besides setting back a couple hundred dollars...

 

I use an old PSU for testing my circuits, i can get 12v, -12v, 5v, 3.3v, 7v, 0v and alsorts of other voltages and i can load it upto 300W, all from an old PSU i ripped out of a machine for free.

Just take a PSU, plug it in, and then short the GREEN wire to any BLACK wire on the ATX connector, i used a peice of wire to do this, jsut stuck it right in the connector, a paperclip would suffice. The power remains on as long as green is shorted to black and the psu has power (duh).

Its an excelent budget solution in my view.

I have a guide (with photo's and info on what every one of the wires does) in the works for pc review (see sig) as part of my 'Electronics 101 Guides'.

 

That’s all I needed to hear…Thanks acrimonious for those encouraging words and I’ll be right over to check out your guide. Did you mod your PSU for variable voltage, meters and such? I really would like to build a high-end Test Bench Power Supply.

 

No i haven't added any modifications to it as such, i've decreased the fan speed to keep the noise down, since i wont be putting anywhere near 300W load on it it should run fine without the fan on full.

Variable voltage because a little more tricky but its possible and to monitor the lines with a voltmeter and an amp meter is easilly done. I might look into including the meters in my guide at a later stage, i'll have to order the componenets first though.

 

acrimonious,
Is there any reading that you know of that might help me with the variable voltage end of this project?

 

The easiest way is to feed all the lines into 2 12Pole rotary switches. You could get LOADS of different voltages from that.

Other options your looking at a variable voltage regulator like the one in this bit-tech fan bus: http://bit-tech.net/article/52/5

 

Couldn’t I tap into the power circuit on the other side of the rectifier and go from there for the variable voltage and current?

 

You could but you'd be in deep water. In the end you would only need to rectify the output again.

 

My bad….I should have said “on the rectified end of the rectifier”. That would give me the starting point of the DC current on the PSU and then (from what I have been reading) go from there or will that hurt the PSU in some way?

Or…I found this PS schematic on the net and noticed that the bottom circuit is what I would need to add to the PSU but it starts right after the step down trans. Would this be a better solution?

PS Schematic

 

How much regulation do you want?

If you only want between 0v and 12v then this is no issue at all, just puttinga regulator on a 12v line.

If you watn between -12 and 24v then it gets tricky, very tricky indeed, and because of the way the PSU is you'll only be able to draw small currents.

 

I don't need anything special really. I’ve done some looking around at test bench power supplies and they all pretty much have the same features give or take a few. I just thought it would be a neat project to do but hearing what you have to say, a computer PSU conversion would be ok for some applications but not as a general test bench power supply. I guess I’ll have to build one from scratch and hope it works when I'm done…

 

I'm building a bench PSU of this type at the moment. Basicially I'm having +5, +12 and a variable power output, a 7-segment LED voltmeter display (which was about £12 as a kit from Quasar electronics if memory serves correctly) and fused outputs. I'm using a MIC2941ABT based regulator circuit for the variable output from http://www.cpemma.co.uk/reg.html. All this in a nice sturdy MDF box with brushed aluminium front panel for the 4mm sockets, controls and dials etc.

This is how it's looking so far:

 

Cool...I'm going to continue with building the bench PS.

I have a noob question What is the average current requirement for most electronic projects? I found a PS schematic at Sam Electronic Circuits (tons of stuff) that is essentially two separate power circuits sharing one power source. One is a +4.5V-25V 15A circuit and the other is 1.25V-25V 3A. Which of the two would be the best to integrate into my project? I am planning on tapping into the PSU on the sec. side of the first trans. like the schematic shows.

Any other comments would be appreciated…Thanks!

 

I think the 3A circuit will suffice…Any comment before I continue?

I'm having trouble finding the stepped down voltage…
I follow the mains to the (yellow) circuit board and it goes to this rec. D5SBA60 50 (red). On the AC side of the rec I get 116V+-, but on the DC side I get 1 on the multi…Where did I go wrong? What is the purpose of the coil with the yellow band if it does not reduce voltage? I get 116V+- on both sides of it.

 

Could someone please help me...I don't understand what is going on in this PSU...

Thanks!