Hey everyone.I am new and the reason which i registered here is because i couldnt find some information i wanted with search engines.So i hope you could help me.
Since summer came my cable modem is overheating(no theres no failure).So i want to cool it a bit.The only way i think and want is to supply the fan with power from the USB.
I found some things about the power of the USB http://www.frontx.com/cpx108_2.html and i noticed that USB gives only 5V.Will my fan work?(even in lower rpms).If so which wires should i connect?
Thanks everyone and cu again.

I'm using an Antec USB fan to cool an external HD and also blow on the rear of my hot-running LCD monitor. Works good, and fairly quiet after I made some rubber feet for it. Cost $8 at CompUSA.

malakas: take a look at your fan's datasheet and take a look at starting voltage, but I think you won't have any trouble to start it with 5V, try it.
You'll only get 5V from USB and you have to use the outter pins of it, just try it.
Be warned, you cannot take more than 500mA from it!

Good.thanks.i knew there people in this forum that know many things!

i know what your name means!

Good,lets keep it a secret!

Note that the recuired current draw that USB must supply is 100mA. So if your fan uses more than 0.1A at 5V you might need a powered USB hub in between.
Using a 12V DC wall-wart and possibly a fanmate seems like an easier solution.

I dont think you'll need a high current fan for this application, something like the 40mm delta would be more than enough and wouldn't suck much power at all. I'm tempted to mod one into my mouse, for the occasional blast of de-sweating air.

griff

yuck. i'd vote to tap power off the wall-wart for the cable modem.

USB's amperage rating is 500mA, so 0.5A.

http://www.metku.net/index.html?sect=vi ... /index_eng

I wouldnt worry, a fan this small running at 5V won't even pull 100mA, which is even under the standby rating. You may want to put a small capacitor across the fan just to remove any ripple you might inject into the supply, but i'm quite sure the PSU will deal with that.

griff

if they could do that do bowling balls, then they wouldn't need the fan on the end of the ball-return thing.

maybe the next big thing will be a mouse with a TEC and cooling fins. When you hold down both mouse buttons the scroll wheel adjusts the temperature.

i kid, only. i admire all the folks out there who are willing to crack a case (or mouse) open to make it work the way they want it to. too may people treat computers like boxes of magic.

This depends on the fan, you have to worry about this, before connecting a fan to an USB port you have to check it's amperage, and on 5V the fan's amperage goes up.

Well, the 500mA is the current the system needs to be able to power an USB hub with device(s) in parasitic mode. This is not the same as saying that devices may use 500mA from the USB port.
Checking the complience guidelines:
http://www.usb.org/developers/compliance/
Periferal decive testing requirements, and then bring up the PDF that is the checklist.
Section 4.1.1, point LP8 is the most appropriate at this point.
Basicly a device may draw no more than 100mA except that it is allowed to charge a capacitor of no more than 10uF with higher current.
The current to charge the 10uF capacitor will be provided by a required capacitor on the USB hub side that is substansially larger.

So it might work to draw more power, but 100mA continous power is the max you may use and still be a USB complient device.
Note that fans does often have a rather high spike on the startup current. This is likely to be more than 100mA.
I would also suggest a diod in parallell with the fan (reversed ofcourse) unless you are sure it is buildt into the fan allready.

!!! what? running on lower voltage draws more current? fraid not...

V=IR

if R is fixed, then if V reduces, I must reduce accordingly..

griff

Isnt firewire 12V? and much higher amp ratings?

IF the fan was desinged to run on 12v it will push very little air and use very little current @ 5V, if it is a usb fan and designed to run @ 5V then it will probably use twice the curent to make up for the reduced voltage.

You're absolutely right. Now i hate to be prissy, but look back to the first thread. This guy is having no problems with his actual modem operation, he just wants it a little cooler. We know it's far better to have a little airflow than none at all - i was going to reccomend either the delta 40mm, if it didnt need much airflow, or just a panaflo at 5V. Both of these woud pull less tha 100mA and would cool the modem down.

griff

Here's one from NewEgg for $6. They come with a little stand....just plug it in. Sit it on top of your modem and it should provide sufficient airflow.

Looking at the picture that fan has dual USB plugs.
I guess that has to do with the need for power, much like the latest graphics cards that have dual power connectors.
A wild guess is that this fan needs two connectors to be able to comply with USB standards. To make good use of the cables you should connect it to two different USB hubs, but that is rarely a practical solution. Using up two adjacent USB ports is mostly to make sure no other device will compete for the power.