Powering fans by USB?????

[Anubis_386]

I got aload of spare 80mm fans and CPU coolers lying around n I was wondering if its possible to buy or make something so you can power em by USB ..... They are all 12V with either 4 or 3 pin connectors ..... failing that .... is it possible to mod a PSU to work without a mobo?

[dwschoon]

I know that if you bridge 2 of the pins on the atx connector of a ps, the ps will start up. I dont know which ones though.

[Agentorange88]

You can make some power supplys run without anything connected. Bassicly you need to connect two pins on the main connector of the power supply. I can't recal which exact pins they are, but I know one is a ground and the other I beleive is a 12v. I would suggest searching the case and power supply section to find out exactly which pins they are. If you power supply doesn't start then it needs a load on it. Some people like to use old hard drives. Just be carefull when messing around with a power supply, they can kill you if you dont know what you'r doing.

EDIT: link I found that might be of some use.
http://www.hardwaremods.com/guides/psu_jump/psu_jumping.html

[Anubis_386]

Ok thanks - that website is very helpfull. Back to the USB thing .... any ideas?

[Roofles]

If you can find fans that run at 5V and use less than 100mA (USB 1.0) or 500mA (USB 2.0) then yes, you could run fans off your usb plug.

Also you could boost the voltage using some ic's, but they wont be able to draw enough current to run a fan at 12V.

[Anubis_386]

Well bang goes that idea - i'll just jump an old PSU and use that.

Thanks :beer:

[four4875]

you cant get one of the little dip packaged buck inverters the boost 5 to 12 v, and be able to handle like a 120 ma load on the 12v side, and have like 50% efficiency?
(120 ma seens like a decent load for a fan at 12V, if its a weak fan lol.)

seems that it should all run just under 500ma.

anyone know how much power the keyboard is rated for? that seems like a more likely port to use. ive seen some older mobos with a 5A fuse on the board and thats about it limitin the power to the kb, but these were socket 7s.

[Roofles]

you cant get one of the little dip packaged buck inverters the boost 5 to 12 v, and be able to handle like a 120 ma load on the 12v side, and have like 50% efficiency?
(120 ma seens like a decent load for a fan at 12V, if its a weak fan lol.)



You are correct in that there are IC's that exist to boost 5V to 12V but in that transition the power must be equal. Power = Voltage * Current. 5V * .5mA = 2.5W and then that 2.5W must be transfered to the other side at 12V which means (assuming no power lost to heat or inefficiency) that you get 208mA at the output. Most fans I know run about .6 Amps, at least ones you would use for cooling.

Now I know they make usb fan coolers for laptops but those are not very powerful.

Another side note, most motors pull 3-10 times (based on rating) the current upon start up. Only for a short period of time, but if you use a chip that is only rated for nearly what it is running at, you run the risk of frying it. A common rule is that you buy something rated at double what its running at.

[ThePCGuy]

I'd personally walk from the idea of USB powered fans based on the info above, and if you've recently looked at the size of the conductors that hook that usb port up to your motherboard? I'm guessing 22-24 guage. In order to jump a powersupply without a motherboard, you need to bridge the green wire in the atx plug, with a ground source. Now maybe someone else can chime in here, because I believe that you can turn the supply on that way, but if you remove it, it immediately turns off. I'm not sure if you could simply use a switch on it, so lets hear some ideas.

- Jim