Older cpu fans with the round thing on the wire

[keymaker]

It's a round charcoal color thing, the wire goes through it wrapping around it... I use to see them alot
What do they do<p>
Also, those little 2" cpu fans, running on a car battery, bad idea?
I'm giving one a "stress test" right now,
or will they only draw what they can handle/need?

[chessman]

They'll draw what they can handle/need. As long as the voltage is correct. Check for "12V" somewhere on the fan's label. If it says "5V" it'll be toast, unless you rig up a voltage drop.<p>The round thing is called a "choke" it's a ferride core that, when the wire is wrapped around it, helps reduce electromagnetic interference generated by the fan on the power busses.<p>It's not absolutely necessary to have there, and it won't hurt anything to be there.

[Gary]

Harbour Freight sells a 5watt 12v solar cell for about $35.00 on sale. Runs the larger computer power supply type fan quite well on sunny days to try to keep the car cooler. These fans don't use much power and using a solar p.v. panel acts as its own controller. Put one on a car last June and the glue attaching the panel to the trunk, just started to give way, so put it away in the trunk until summer.<p>In my case, the trick is to get the hot air out of the cab and out of the car without the fan air "short-circuiting". That is, blowing out the cab into the trunk and the air getting back into the cab through the little fabric covered holes. I need to add some kind of duct system to mine.<p>What are you using your fan for?