Convert an ATX Power Supply Into a Regular DC Power Supply!

Step 8 Conclusion

My 400 Watt power supply can deliver 23 Amps through the 12V rail, and 40 Amps through the 5V. That's very good for something that, aside from the initial cost of the PSU, cost about $10.

Comments

[Blacklight [HUN]]

Nice job.
My problem is that I can't run a zvs driver (pulls around 5A at 24V), a plasma speaker either.
It just simply turns off.
What could be the problem? :S

[louige99]

well you have 24V at 5A which is 120W, i assume your PSU is rated above that but that doesnt really mean much at all. most PSU's only allow certain max power for a combination of rails. For instance, a PSU with a 12V, 5V, and 3.3V rail might be rated at 250W, but the combined wattage of the 5V and 3.3V rails might only be 110W.

In short, check what specific ratings are on the stickers on the PSU and search the internet for the data sheet if you can find it. If you cant, i would say thats your problem and you can really only fix it by getting a new PSU that has a 25V 5A rating on it

[NiKiToS]

In the other instructable they had a fuse connected to each voltage output, is it really needed?

[sschoemann]

no BUT any equipment you power with it (other than low current experimental circuits) should have it's own fuse, at it's specific rated current.

[ivaneduardo747]

No, the ATX specification says that every power supply must handle over-current situations where the current is too high for the supply's capability. Also, it will shut down on short circuits.

[wlaukaitis]

Hey this looks great! I have a little Dell i want to convert. I have a question though...

Isn't is 400w@12v?

instead of 400w@120v

[joinaqd]

wow 400 Watts...wonder how much its cost is per hour to operate?

I=V/P
= 120/400
= 0.3 Amps
Wow dude thats a lot current

[7862Tony]

400 Watts is what the supply is capable of delivering ,not what it consumes!!
These PS are brilliant. Do not forget to add a push button momentarily ON switch ,from the green wire to 1 of the blacks. this will start the P.S. Also before one can work out consumption , one have to know the efficiency of the P.S.

[INDUCTION_MIND]

i think you meant to:
400w/120v = 3.33 amps

[joinaqd]

Ur correct , my bad, i was sleepy that day..

[ste5442]

I wish I could make a supply as efficient as this :-)
Sounds like the answer to the worlds energy problems!
A simple mixup - think of P=IV as a triangle with P at the top and I and V at the bottom. P/I=V, P/V=I, IV=P.

PCBPolice

[thetech101]

You got that almost perfectly backwards. It's P = V * I.
400 W = 120 V * I.
400 W / 120 V = I.
I = 3.33333333 A.

That's nto so much current.
In my area it's .10 per kwh. Or .04 cents.

[JakeTobak]

400 W = 0.4 kW
0.4 kW * 1 hour = 0.4 kWh
Depending on where you live, that might be 4-7 cents an hour I estimate.

[danlab]

That is only if you run the thing at full power, under most conditions it won't use nearly as much power as it is rated for.

[chuckr44]

In Michigan power is 8.8 centers per kwh.

[chuckr44]

Should be "8.8 cents per kwh".

[awang8]

400 watts

I=V/P

240/400

0.6 Amps

Mains = 240v @10 Amps

240x10=2400

400=2400

4/24

2/12

1/6

1/6th of total mains power = 0.6 Amps. There you go.

[Sparkington]

600 mA is not a lot of current, I have seen bigger toaster before that require 25A connections.

[joinaqd]

woops! my bad! i did the math wrong!

[sschoemann]

I think a bunch of you need this rather badly!

http://www.the12volt.com/ohm/ohmslawcalculators.asp

[MACSWAG]

wow!can you do this and make it do 24 v dc.

[Thav]

There should also be a -12V line floating around in the power supply somewhere. If you bring the -12V out to the front, you can connect your circuit from -12V to +12V to get 24V DC. There are two things to watch out for. That 24V will NOT be ground referenced like you might imagine, so if you hook an oscilloscope to the -12V to measure up to the +12V line (to see your shiny new 24V supply) you stand a very good chance of toasting your circuit or your oscilloscope because one of the scope's leads is usually a low impedance connection to ground. If you have isolated probes, that's another thing, but those are more expensive and it's unlikely that most people will have them. Less importantly, the 24V supply you make will likely be able to supply much less power than then +12V supply alone, because the -12V is usually limited maybe 50 times less than the +12V, so you might only get about two times the -12V rated power from the 24V supply. If you need more power than that, you might want to look into DC-DC power converters.

[dcallaghan]

Yes some maths wrong there:

I=P/V, I=400/120, I=3.33'A (I=1.66'A @ 240VAC)

I dont know why you would calculate the current as mains is sold in kWh anyway.

As the supply wont be 100% efficient the input power will be higher than 400W when the outputs are loaded up to 400W.

You can get 24VDC by using the -12V and 12V wires although current will be limited to what the -12V output can provide.

[francoiskapp]

Other than the incorrect maths, you guys are also forgetting that you don't use the maximum power all the time. The typical efficiency of ATX supplies comes down at the low power end, but it is still not too bad. So if you are only taking out a couple of watts on the output and wasting a few watts in the supply, those are the numbers you should use in your calculation.

[omikun]

The 120Volt is the AC input. The output voltages are in 3.3, 5, and 12V.

[francoiskapp]

Just a small warning: Most ATX supplies have a minimum current on one (or two) rails below which regulation is not guaranteed. I've done this many times and I have not yet had problems, but just in case I started adding a minimum load resistor to the rails in question. It's a bit wasteful though, so for non-critical use, leave it out. I also add an LED on the POWER OK and a switch on the PSU ON, but that's not really needed.

[ste5442]

I think the ATX spec states that the power supplies should reach their target voltage (and be within spec) with no load now.
There may be older supplies which need a minimum load though?

Good work on the 'ible :-)

PCBPolice