Computer power supply to power fans

IslandCrow

IslandCrow

Reef Monkey
Premium Member
I have an old 300W computer power supply I thought would be convenient to power computer fans for my tank. Overkill, I know, but I don't see myself using it for anything else. The problem I'm having is that since it's not getting a signal from the computer, it won't turn on by itself. At least, that's what I'm assuming the problem is. If my guess is correct, is there a way to hardwire it so I can use the power supply without a computer?
 
I'm assuming this is an ATX power supply then. Yes there is a way to get it to turn on. You jumper the green wire to any black wire on the ATX connector. A paper clip cut down and bent in half works great.
 
Just to add to this AT power supplies will have a switch attached to them. When ATX power supplies came around they wanted the power switch on the front of the computer to be a soft switch. Meaning it would signal the mother board, which in turn the OS can decide whether it should shutdown, sleep, etc depending on settings. Depending on the BIOS settings holding the power button for 3 seconds will signal the motherboard to immediately cut the power. The motherboard controls the power supply by ground the green wire.

By jumpering the green wire to black you are grounding it and signaling the power supply to turn on.
 
686 is right. the black and green wires need to be connected. I cut them off at the connector and spliced them together. Most power supplies have a swith on the back, you could use that to turn it on/off


i used this
 
Don't do it. Get a DC converter at radio shack to power the fans. Less power.

Or just buy a couple of computer fans that are AC - that is what I did.
 
I agree the AC to DC converter is the cleaner way to do it, but its not dangerous to jumper those two pins together. Your just signaling the power supply to turn on just like the computer motherboard would.

The computer power supply is probably safer in one aspect that if you short anything out it will immediately shutdown without causing damage. I've seen this first hand. Plus all the wires coming out of the power supply only contain a max of 12 volts anyway.

FYI I've been building computers for over 10 years.
 
So are you saying my 300W power supply is going to use 300W regardless of what it's powering, or is it just inefficient in another way? If it's the former, I think I agree that it would be a huge waste of power.
 
No its not going to use 300watt regardless. That would be ridiculous and business would be going bankrupt trying to run their server racks.

I have an Antec 430 watt power supply in my system. With the computer, dual monitors, printer my 700VA 450watt UPS is less than half load. That alone proves my point above.

Although I would say that a dedicated AC to 12V DC converter would beat the power supply in terms of efficiency since it is made for that purpose. Computer power supplies are made to put out higher currents and multiple voltages.
 
OK, that's probably what they were getting at then: it's simply not as efficient. It didn't make sense it would use the entire 300 watts, but I figured the dumbest question is the one that's not asked. I'm not too concerned about wasting a few watts here and there. I may still go with an AC-DC converter for size reasons if nothing else. Guess I have a little more to think about. If nothing else, I've certainly learned a thing or two. Thanks for all the input so far. It's been quite helpful.
 
<a href=showthread.php?s=&postid=9769400#post9769400 target=_blank>Originally posted</a> by IslandCrow
OK, that's probably what they were getting at then: it's simply not as efficient.
Click to expand...


It really depends on the wallwart, and the powersupply.

If you buy cheap, in either case, theyre not going to be efficient.
 
I think you might be better off just going to Radio Shack and get 12 volt AC/DC power adapter and just splice it. You can use a Terminal strip if you have more than 1 fan.
 
An AC to DC power supply would be better than using a PC power supply. A pc power supply has enough amperage in it even when unplugged to KILL. The capacitors can store enormus ammounts of power for days or weeks and still discharge. Not to mention that you are going to try to use this in an environment that will have high humidity and liquids. Plus the powersupply will generate not only 12v but 5v and 3.3v and though you will not be using the other power rails it will still be generating that power. No it won't be much but it will be there.

If you are dead set on using the power supply you may want to get something like http://www.cyberguys.com/templates/searchdetail.asp?productID=2531 It will at least give you a led to show that the power is on and you will cap the ends of the MB connector.

But as suggested it is much safer and smarter to use a power brick. BTW I have seen a powersupply discharge and knock someone on the floor, not a pretty sight.
 
Island,

Nightshade is correct you could be seriously injured using a PC psp to operate a simple fan.
My solution:
I had an unneeded AC to DC transformer from an answering machine that had an output of 12 VDC and supplied enough Ma to run the 3" PC fan. All I needed to do was chop the connector end off of
the wire and use water proof butt connectors to get everything working.
Also a PC fan will run at 9 VDC to allow slower air flow. Sometimes if air is moving too fast there will be little to no heat exchange taking place.
Example: using 2 fans in a custom lamp fixture, one fan pulls air in and the other pushes the air out.
Hope this helps.

Barry
 
OK, you guys have convinced me. I'll go ahead and heed all those warnings on the power supply and not use it for this. I wouldn't have kept it too near the fishtank, but I agree that it's probably just not worth it. Our local Radio Shack guy looked at me like I was speaking Japanese when I asked him about an AC/DC transformer, and finally showed me one for $60 that even price aside wasn't really what I wanted. I'll probably just order one online and save myself all the hassle, since I'm not in any real hurry.

Thanks, everyone. Again, I appreciate all the help and advice.
 
RadioShack sells them

1000mA model

http://www.radioshack.com/product/i...r=1&origkw=12v+dc&kw=12v+dc&parentPage=search

1500mA model
http://www.radioshack.com/product/i...r=1&origkw=12v+dc&kw=12v+dc&parentPage=search

If you go this route get the adaptaplug project connector so you can easily unplug the power brick from the fans. Makes it easier to route the wires.

http://www.radioshack.com/product/i...kw=adaptaplug&kw=adaptaplug&parentPage=search

I've used the 1000mA model with 2 temperature controlled computer fans to keep a in wall projector box cool.
 
Actually, I just happened to have an old multi-charger lying around. It's 600mA with variable voltage settings from 2.5-12V. It looks like it powers 4 fans without a problem, so I think I'm set for now. I like that one from Fry's, though. If I need a second one (which I very well may), that's definitely a candidate.
 
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