Introduction: Cheap (AXT) Bench Power Supply 30 Amps!

Picture of Cheap (AXT) Bench Power Supply 30 Amps!

This is my second PSU (Power supply Unit) as my prievieous one mysteriously burnt out (!)
I managed to purchace a new Computer PSU to convert, this one has a nice jucy 5V at 30A! and 12V at 21A!
I also managed to get a 30A panel Ammeter Yay!
Any comments welcome!
(Plz dun be too harsh lol)


corradini (author)2015-10-27

I'm sorry - is this an Instructable?

I'm trying hard to stay inside the "be-nice" comment policy: but what I see here is 11 photos. No directions. No parts list. Might be mostly a 'selfie', not 'helpie'. >;-)

And, given that we're dealing with potentially lethal, or at least super-painful, voltage discharges -- I think it's really irresponsible to post *anything* about an ATX power supply project without significant instructions. (Let alone safety disclaimer/warnings.)

If this is an "Instructable" - there should be "Instruct-tions". If not, it *may* not belong here.

MohitS17 (author)2015-09-08

I built my power supply with the similar instructions as yours using only the 12Volt output to power my Car Airpump (12V 14Amp max).I joined all 5 12V wires (Yellow) together and same for the ground connections to get the max current on the 12V rail which is rated for 17A on this supply.

With no load connected, the SMPS turns on and works fine but as soon as i connect the Car Airpump it trips (shuts itself down) not sure why ?

Now if i connect the same Power supply with a Digital Ampere meter connected in series, the Air Pump works perfectly. Could you help me understand the possible cause for this behaviour and how could i go about fixing or diagnosing it.

amclaussen (author)2015-03-18

You said: "as my prievieous one mysteriously burnt out (!)

Me too!

My first power supply was working OK when supplying close to 7.1 Amps at 12V to an intelligent battery charger. But one day it just stopped working. Fuse was intact and there were no visibly burned parts. That one was rated at 230 watts and its +12V output was supposed to be "9 A".

A second one with even more rated power ("13A") also burned.

Maybe we need to consider that these power supplies were NOT meant to supply a CONTINUOUS full current output... as the computers they feed do not pull afull current for many minutes or hours. Maybe some parts inside the supplies are not up to the task and fail sooner or later. Or some components are of dubious quality (Capacitors?).

Anyone can help with explaining the reasons for failure? Another hint is that the 12VDC output barely reaches about 11.8 V when producing more than 6 Amps...

As I will be using this same charger for a long time, I want to be sure there is a computer power supply that can provide at least 15 Amps at 12 V, just to be sure it will endure. (my power supply modification is used for 12VDC suppy only, for chaging batteries mainly, and the 5 V output is loaded with a 6V automotive light bulb in order to raise the 12V output to near 11.97 VDC at full load when charging a 12V auto battery. Amclaussen.

russ_hensel (author)2015-01-09

Just a note to let you know I have added this instructable to the collection:
Encyclopedia of ATX to Bench Power Supply Conversion
Take a look at about 70 different approaches to this project.

usafbrat (author)2013-07-13

How can you regulate the current, I dont want to blow up any of my components. Any where from (1-Max) amps. Please Help!!!

Vorpaxis (author)usafbrat2014-03-30

This is a belated answer but it doesn't seem to have been answered. You can use a current divider to regulate the current coming out of the PSU. Use a potentiometer to vary one of the resistances to get a variable current.

mikedoth (author)2009-09-26

Don't most home circuits only supply 15 amps?

jhines0042 (author)mikedoth2009-09-27

Yes, 15 amps at 120 volts AC in the US anyway. Sometimes you will find 20 amp wall service, the outlet has a separate little tab cut into it to indicate.

For the rest of the world, check this page on wikipedia:

The thing is that the OUTPUT of the Power supply is not at 120 volts. So the amperage can be boosted as the voltage is dropped.

muttyfutty (author)jhines00422009-09-28

Sorry, lol I ment 'no' as in you didn't understand, not that home circuits dont provide 15A (actually its 13A for 240V and 15A for 120V (I think!)) but you can get larger ampage ones for cookers, ovens etc...

jhines0042 (author)muttyfutty2009-09-28

I knew what you meant, I was simply trying to help clarify your point. Nice instructable, btw. I will probably make one of these myself at some point.

muttyfutty (author)jhines00422009-09-28

Oh, Ok sorry lol thanks,I wish I documented the making so I could make a I'ble oh well, I'm currently working on a flyback driver, hmm...

tstreet1 (author)muttyfutty2011-08-17

Dude, you should post a link to your flyback driver. I'd like to check it out.

mikedoth (author)jhines00422009-09-28

"So the amperage can be boosted as the voltage is dropped." How in the world is this possible?

jhines0042 (author)mikedoth2009-09-29

This link has a great explanation of this exact principle.

Basically if you cut the voltage in half with a transformer you necessarily increase the amperage by a factor of 2. A mathematician would say they are dependent variables.

carlos66ba (author)mikedoth2009-09-28

At 120V, a good power supply has a pretty good energy efficiency. Power = Voltage * Current (roughly speaking, there are some refinements needed for AC). Hence, 5V * 30A = 150 W, only ca. 1.3 A at 120 V, say a bit more because of inefficiency, still leaves things well-below the 15 A...

muttyfutty (author)mikedoth2009-09-27

No, Sorry I should have been more clear,
its 30A output

Quackoman (author)2011-04-14

the ammeter you found looks good but if the max out is 30A you should have gotten an ammeter that can read just above btw it looks very neat.

AngelLaHash (author)2010-06-17

Personaly i just got a light switch and hooked a ATX connection (24pin i think) to one end and 5v/12v on the other.. that way i figured i could use any ATX PSU i wanted. I love the Amp meter tho .. maybe write what connector is what on the case.

kiiko (author)2009-12-20

hehe cool, your tabel looks like mine ^^. lods of fun stuff

muttyfutty (author)kiiko2009-12-20

I really need to tidy that mess up!
can't find my little snipper things...

pjharro (author)2009-10-16

Would you please be able to briefly explain your wiring? What do the lights do?


muttyfutty (author)pjharro2009-10-21

Sorry for the late reply, I've been very buisy!
The Orange light is the mains on light
The large toggleswitch is the mains on/off
The red light is the system O.k indicator, it is connected to the 12V rail
And the small toggleswitch is the system on/off, it connects the Grey,green wires which have to be connected in order for the PSU to work.
Hope I helped!

bumsugger (author)2009-09-29

Looks good,any chance of a ctt. diagram,plus a few "build" details??

muttyfutty (author)bumsugger2009-09-30

well, Ctt diagram, hmmmm. all I did is just erm... hang on...

muttyfutty (author)2009-09-29

O.o ???

About This Instructable




Bio: A li'l kid from Inkland (England if you can't take a joke) High voltage is awesome, so is pie. Lemon Pie is good ... More »
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