# I have a small fan that I want to hook up to my usb port...

but it's a 12 volt not a 6 volt, and it runs to slow on 6 volts. what do I do?

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dog digger says: Apr 11, 2012. 1:15 AM
you can get a voltage booster circuit to step up the voltage to 12v
sahat says: Sep 12, 2010. 11:05 PM
I will assume you are using 12v fan for computer(brushless) and I think it doesn't design for USB which only 5V.

If you insist to keep using that fan to be powered by USB you need to build some kind of power converter to set up the voltage(such as mentioned by frollard)

But if you asking me what will I do, then I probably just buy a USB powered laptop cooler pad and use their fan since it was design to work on 5V USB power.

Regards
mantosh says: Jun 5, 2010. 7:47 AM
you could make it so it plugs into two usbs and combined the power to make it powerful enough
msw100 says: Jan 9, 2010. 10:11 AM
Buy one from a £1.00 shop
psymansays says: Apr 28, 2009. 7:17 PM
A lot of fans use over 1000 milliwatts, running at 12V. At 5V, that may still be over the 500 milliamp limit of the USB port.
frollard in reply to psymansaysApr 29, 2009. 12:12 AM
5v@.5a = 2.5 watts
1000 milliwatts is less than 2500 milliwatts - hence why I said to do the math for the guy :D
psymansays in reply to frollardApr 29, 2009. 10:01 AM
Well, yes, that is true. The thing is, these fans tend to use brushless DC motors, which behave weirdly when running under voltage, often drawing more current than they're rated for. It would be best to use a multimeter to check the amperage from a stronger 5V source before hooking it up to a USB port, is all.
frollard in reply to psymansaysApr 29, 2009. 11:43 PM
Indeed - undervolting a given impedance or resistance will result in higher current to make up the difference.
fwjs28 says: Apr 28, 2009. 12:27 PM
it will just run slower....

ps, most usb ports are 5 volts
oldanvilyoungsmith (author) in reply to fwjs28Apr 28, 2009. 4:01 PM
oh yeah, I meant 5
frollard in reply to oldanvilyoungsmithApr 28, 2009. 5:04 PM
you need a dc-dc boost converter (think joule thief, but bigger) - it can convert the 5 volts up to 12 volts by using more amps (proportionally) (volts times amps are watts...)
A usb port can deliver 5 volts at ~500 mA, at spec - so thats 2.5 watts. Do not use a fan larger than about 2 watts (it'll say on the fan)...because if you boost 5 volts to 12 volts, then you still only have about 2 watts after conversion / 12 = 167 mA.

A better method would be to wire a 'molex' connector to inside your computer case (assuming not using a laptop) - then extending the cable to where you need it.
oldanvilyoungsmith (author) in reply to frollardApr 28, 2009. 8:23 PM
yes, laptop.
fwjs28 in reply to frollardApr 28, 2009. 5:13 PM
or take two usb cables, plug 'em into two ports, then wire both power wires to the fan, and you would get 10v which is almost 12, but just a tad slower....
oldanvilyoungsmith (author) in reply to fwjs28Apr 28, 2009. 8:24 PM
I tried that at the beginning and it didn't work. (assuming that I did it right)
psymansays in reply to fwjs28Apr 28, 2009. 7:15 PM
That would more likely short out one of your USB ports power line directly to the ground on the other, and blow a fuse or something.
ryan_clarkie_clark in reply to psymansaysMar 21, 2011. 6:36 AM
There are external HDD's that utilize this function exacttly. They connect to an extra USB slot for added power when using laptop systems. I have one and it never shorted out.
fwjs28 in reply to psymansaysApr 29, 2009. 12:16 PM
true....
frollard in reply to fwjs28Apr 28, 2009. 7:11 PM
I think they share a common ground, so if you put +5v from one to ground on the other, you have yourself a short circuit. I could be wrong.
fwjs28 in reply to frollardApr 29, 2009. 12:16 PM
i think your right...you would need some fancy equipments.....