Cheap adjustable PC PSU for test loads!!

Just thought some people might benifit from this web page I came across today and a youtube video, I've been having a problem setting my drivers current because of the batterys loosing voltage before I can set the current, and I needed to find a way of getting a constant 4.2V, and this looks like a nice, easy and best of all cheap way of doing it

I know quite a few people have probabally done a PC PSU before but I thought this was quite a neat simple approach to it, I'm going to be giving it ago over the next few days

Web page:
Building an ATX to bench power supply converter - James Gibbard.co.uk

Video:


Extra links:

This link shows the specifics on how to transform a PSU with just set 12v and 3.3V lines (no adjustable voltage, can be added in next guide)

http://www.wikihow.com/Convert-a-Computer-ATX-Power-Supply-to-a-Lab-Power-Supply

This link shows how to change the PSU into an adjustable voltage bench using LM317 regulator, and the +12V and -12V lines. It is possible to build this circuit in a seperate box from what I understand, then have connectors on the back to just plug a PSU in via normal molex/24 pin connectors and then get an adjustable 24V output. The reason for doing this is you need a -12V line with a minimum rating of 1.5A (info can be found on a sticker on the PSU most of the time) and the minimum 1.5A rating tends to come with the more expensive PSU's that you don't want to rip to bits.

http://www.wikihow.com/Add-Variable-Voltage-to-Your-ATX-Based-Bench-Power-Supply

awesom lm317 tut
http://www.rigacci.org/docs/biblio/online/voltreg/fan-regulator/tutorial-full.html

Thanks for finding this Ash!!! +1 :beer: I've been wanting to build one of these but like you, I really like this different approach.

Ooh, I like that! There's actually quite a bit of space left over in the PSU's, you could probably do it as an all in one.

tj and meatball posted this for me a super long time ago. i wish i had lobbied to get it stickied..

PLEASE STICKY THIS ONE

michael.

Kevlar said:

Thanks for finding this Ash!!! +1 :beer: I've been wanting to build one of these but like you, I really like this different approach.

Click to expand...

Welcome

I think I'm going to end up going the normal route, and build it into the PSU's enclosure because I have one spare.

I'm using this guide to do the PSU:

How to Convert a Computer ATX Power Supply to a Lab Power Supply - wikiHow

and then this guide to build the adjustable voltage circuit:

How to Add Variable Voltage to Your ATX Based Bench Power Supply - wikiHow

If you go this route, I'm going to have the +12v and -12v lines going to the adjustable circuit, from there I'll have an adjustable 24V line going to red and black (GND) terminals, (instead of the normal 3.3V going to red) Then I'll have a separate terminal that's yellow or white or something that will have the 3.3V going to it, just incase I need a specific 3.3V quickly, without adjusting the 24V.

After looking at the LM317 circuit guide, he says that it's important the -12v line is rated for a minimum of 1.5A, but my PSU is only rated for 0.3A which is a bit of an ass, because if I understand it right, that means I can only go up to 0.3A for the test load setting, instead of the 1.3A I might need when setting for 445nm's.

I'll probably build the voltage changing circuit into a separate box, like the original guy does, then have connectors so I can plug in my expensive PSU in and get more than 0.3A, without destroying my PSU.

Actually come to think of it, I only really need the voltage regulating circuit if I go that route

Looking on Newegg at a variety of models and prices of PSU's, none are 1.5A on the -12, they are .08 or .03 the ones I saw. But I only checked about 10 out of a few hundred lol.

Thorsteenster said:

Looking on Newegg at a variety of models and prices of PSU's, none are 1.5A on the -12, they are .08 or .03 the ones I saw. But I only checked about 10 out of a few hundred lol.

Click to expand...

If you have any luck I'd love to know, I'm starting to doubt whether you actually need the high amperage on the -12V line, why would the -12v limit the current, when the +12v are like 10-13A.

edit:

scratch that the lower line is what sets the max amperage. I'm thinking because we only need the 4.2V normally for setting a drivers input, it might be possible to use the 5V(red) lines as they seem to rated a lot higher, however on my PSU I can only find

+5VDC and +5Vsb the minimum being Vsb at 2.5A. is the Vsb essentially -5v?

edit edit:

Aparantly the Vsb (purple wire) is the +5V standby wire, not used, and the -5V (white) arn't on the newer supplies, I'm hoping this doesn't mean the 5V lines can't be used with the adjustable regulators.

I've been reading a few tutorials, and even though I can't seem to find a PSU with a higher -12V line than 0.8A, quite a few of the tutorials are quoting a maximum current on the adjustable voltage of 1.5A (LM317 limit.)

Is there a way of getting the adjustable voltage with out having to use the -12V line? and use just the +12V line with the high current rating?

Would you input into the adjustable voltage circuit the +12V line and the GND (black) wires? instead of the -12V?

I'm not interested in 22V, if I can get 1.5A from just the +12V line.

Cheers

in the mean time, I'm going to try and find an old PSU with a -5V as they tend to have high current lines, and I don't need anything above 4.2V.

edit:

Sorry if I'm rambling a little but
I believe after some more reading, you can just use the +12V line and the black GND line as the input to the regulating circuit, then you arn't limited by the -12V low current. This is fine for us as we won't need anything above 12V for lasers anyways, on my PSU I can draw upto 13A on the 12V line, so I'm going to look at using another LM regulator to get a little more current than 1.5A that the LM317T will supply.

Spent most of yesterday and this morning get a supply running with a variable LM317 12v feed.

Finally got it working, after a few hicups such as having too insulate the binding post for the +12V as it was shorting with the case, and other things such as space constrictions moving the fan around and getting all the bits fitted and soldered up.

Then, after everything was finally sorted, I put it put the top cover with all the parts on including the LM317 cirucit and it's heatsink, screwed it down flicked it on and then got a large spark out of the fan gril into my chest (scared the crap outta me) and a large bang, the heatsink on the LM317 shorted on the PSU's heatsink and blew the 1uF cap on the LM317 circuit, sods law it's the only componant I had one of and the only part they're out of stock at maplins.

Look's like I'll have to wait a few days, probabally have to find a new PSU as well as this one won't turn on, could be a blown fuse but anyways, atleast I know it's all working, just gotta watch out for heatsink insulation

Not to derail this completely, but I'm curious if anyone has tried anything like this with a PC Power supply.

Bench Supply from PC Power Supply (ATX PS Adapter) | eBay

I see these all the time on eBay, but have no idea if they are worth anything. I've been considering purchasing one, since I always have an abundance of PC power supplies sitting around.

Ive built One similar to the one in the OP. Right now its Just Loose and Not in a In closer. Iam Using a LM350 Regulator to make it Adjustable.

If your on a budget its a Great Project.

The Only thing i do not like is when you shut of the supply it does a little Spike at the end.

So Now when iam using it i got into the habit of Unplugging the + or - that is going to the driver before i shut the Supply off so it does not allow the spike to pass through the driver.

Iam getting one of those cheaper Power supply on Ebay Next week. Cant wait to get it.
MASTECH VARIABLE DC POWER SUPPLY (HY1505D)0-15 V/ 0-5A | eBay

Edit:
Must Of Rep'ed you earlier. Wont let me Now.

lazeerer said:

Ive built One similar to the one in the OP. Right now its Just Loose and Not in a In closer. Iam Using a LM350 Regulator to make it Adjustable.

If your on a budget its a Great Project.

The Only thing i do not like is when you shut of the supply it does a little Spike at the end.

So Now when iam using it i got into the habit of Unplugging the + or - that is going to the driver before i shut the Supply off so it does not allow the spike to pass through the driver.

Iam getting one of those cheaper Power supply on Ebay Next week. Cant wait to get it.
MASTECH VARIABLE DC POWER SUPPLY (HY1505D)0-15 V/ 0-5A | eBay

Edit:
Must Of Rep'ed you earlier. Wont let me Now.

Click to expand...

I was looking at trying to get hold of the LM350 but I couldn't find one locally which is a shame, the extra current would be nice compared to the 1.5A limit on the 317

I think since I've now extracted all the supplies from the previous blown PSU, I'm gonna get some male 24 pin connectors (I think male the ones that clip into the connectors coming from the PSU) and mount the circuit in a detatchable box to save trying to squeeze it into the PSU's enclosure.

^PM Me.