Can a fan be powered via a USB port?

Fuzzilla · Post by **Fuzzilla** » Tue Sep 11, 2007 2:32 pm

I have this idea...

I want to add a cooling fan to the home theater. The DVR has USB ports. I have 12v fans.

Can a USB port send 12v to a 12v fan?

It seems like it should work, a Antec P182SE has that spotlight that runs off the internal USB connector on a modern mobo.

cansan · Post by **cansan** » Tue Sep 11, 2007 3:25 pm

Nope, I think USB is 5 volts and 0.5 amps max, for a total of 2.5 watts.

bonestonne · Post by **bonestonne** » Tue Sep 11, 2007 4:30 pm

Well, USB powered fans are possible, however i've only tried it on 80mm fans to date. when you cut up the USB cable, you'll find 5 total wires [Red, Black, Green, White and Ground]. Red goes to Red, Black goes to Black, and you can cut the rest flush with the shrink wrap, they don't matter.

the fan will only work at 5v though, you can't easily get to 12v.

I'm sure its possible to run a fan, but i know for a fact that its much harder to get the fan running at 12v.

it'll take some experimenting. plus, you may only want to use 1 fan per USB port, i don't think daisy-chaining anything will be a good idea on a USB port. I made the one USB fan i have for my laptop, which just so happened to promptly die 3 hours after using it....the fan works fine though, i'm just procrastinating more with that laptop.

Pgh · Post by **Pgh** » Tue Sep 11, 2007 8:12 pm

http://www.performance-pcs.com/catalog/ ... ts_id=1448

FlorisNielssen · Post by **FlorisNielssen** » Wed Sep 12, 2007 2:23 am

It is possible, but, as said, it has a voltage of 5V. And just 100mA. (The maximum of an USB-port is 500mA, but you have to request it. And a fan can't do that. So a maximum of 0.5W.)

A firewire port gives you 12V however. (That's why you should never connect an USB-port to firewire.) Don't know the ampÃ¨rage (valid English word?), though.

Most fans take more than 0.5W to twist. But there are fans that will work. (I thought the noctua's, not sure.) Daisy-chaining will not work.

Fuzzilla · Post by **Fuzzilla** » Wed Sep 12, 2007 7:50 am

Thanks everyone.

FlorisNielssen wrote:It is possible, but, as said, it has a voltage of 5V. And just 100mA. (The maximum of an USB-port is 500mA, but you have to request it. And a fan can't do that. So a maximum of 0.5W.)

A firewire port gives you 12V however. (That's why you should never connect an USB-port to firewire.) Don't know the ampÃ¨rage (valid English word?), though.

Most fans take more than 0.5W to twist. But there are fans that will work. (I thought the noctua's, not sure.) Daisy-chaining will not work.

Cool!. The DVR has firewire ports as well. Does anyone know the wattage/amperage of a firewire port?

flyingsherpa · Post by **flyingsherpa** » Wed Sep 12, 2007 8:20 am

Fuzzilla wrote:Thanks everyone.
The DVR has firewire ports as well. Does anyone know the wattage/amperage of a firewire port?

according to wikipedia,

Its six-wire cable is more flexible than most Parallel SCSI cables and can supply up to 45 watts of power per port at up to 30 volts, allowing moderate-consumption devices to operate without a separate power supply.

so it should handle a fan no problem.

Fuzzilla · Post by **Fuzzilla** » Wed Sep 12, 2007 2:16 pm

Wicked!

Thanksabunch!!

Matzon · Post by **Matzon** » Wed Sep 12, 2007 2:42 pm

I'm running the antec tricool 120mm fan (from a solo case) using my mac mini's usb port, by cutting the usb cable and getting power from that.
Won't start unless the tricool is set to full speed. But once thats done, it runs like a champ.

FlorisNielssen · Post by **FlorisNielssen** » Thu Sep 13, 2007 4:51 am

Matzon wrote:I'm running the antec tricool 120mm fan (from a solo case) using my mac mini's usb port, by cutting the usb cable and getting power from that.
Won't start unless the tricool is set to full speed. But once thats done, it runs like a champ.

Weird, according to this SPCR article, it draws more than 1W of power, so it shouldn't work.. Maybe the USB-port does give more than 100mA?

Fuzzilla · Post by **Fuzzilla** » Fri Sep 14, 2007 3:18 am

From what I understand a USB port will supply up to 500mA of total power.

Bluefront · Post by **Bluefront** » Fri Sep 14, 2007 3:30 am

There are several desk fans available that run off USB ports.....without problems. These are 5V fans, made to run full-speed at 5V. You can find these things sold separately as just the fan.

5v fans

flyingsherpa · Post by **flyingsherpa** » Fri Sep 14, 2007 8:54 am

Fuzzilla wrote:From what I understand a USB port will supply up to 500mA of total power.

<pedant mode>

500ma is current, not power. 500ma * 5V = 2.5W, which is power.

</pedant mode>

FWIW, I've heard some ports can only deliver 100ma, while others can do 500ma. So if you have one that can handle 500ma, you have 2.5W to work with, which I bet should just barely do a low speed fan on a low-ish setting.

FlorisNielssen · Post by **FlorisNielssen** » Sat Sep 15, 2007 7:16 am

Fuzzilla wrote:From what I understand a USB port will supply up to 500mA of total power.

Wikipedia wrote:The USB specification provides a 5 V (volts) supply on a single wire from which connected USB devices may draw power. The specification provides for no more than 5.25 V and no less than 4.75 V (5 VÂ±5%) between the positive and negative bus power lines. Initially, a device is only allowed to draw 100 mA. It may request more current from the upstream device in units of 100 mA up to a maximum of 500 mA.

A device has to negotiate with the port to ask for more power, according to the standard. But some times it seems to be possible to draw 500mA without negotiating, like with Matzon, I suppose.

Matzon wrote:I'm running the antec tricool 120mm fan (from a solo case) using my mac mini's usb port, by cutting the usb cable and getting power from that.
Won't start unless the tricool is set to full speed. But once thats done, it runs like a champ.

Well, that clears some things in my mind.