USB powered desk fan

Sigh, it is the first of April.

I am using this article as a reference for my design...

But you can now buy all kinds of junk that plugs into USB ports merely to get power from the USB port. Fans, LED lights, cellphones and IPods so you can charge them, some things even more nonsensical.

Michael

A fan?

I would rather build the fan myself because if looks like a fun project. I calculated from ohms law v=ir that if v=3 and i=2.8amps (2 standard AA batteries) then r=1.07 ohms. Are my calculations and units correct? I went to radio shack earlier but could not find a

1ohm resistor or potentiometer. Do I have my units off in my calculations? Am I thinking about this incorrectly?

A fan has to move enough air to make one feel noticeably cooler. This is mostly based on evaporation from the skin and air flow. People who can't sweat don't appreciate fans. Battery operated fans normally must be held about 5 inches from one's face to achieve any effect. USB power limits would make for an anemic fan.

This is simply April 1, which follows March madness, el-regurgitatia.

Your calculations used the wrong data.

A properly designed USB port only supplies 1/2 amp.

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

If there are no outlets, how are you powering your computer? If there are no outlets, why hasn't the building inspector condemned your office?

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

wow. lots of bird walking going on here. i just want to know if i can put a resistor in series to reduce 5v to 3v and what the value of the resistor would be. if anyone has the ability to answer this question please help. otherwise please leave your 2 cents in your pocket.

This has nothing to do with challenges.

If you asked "can I hook up a fan to a USB port", you'd likely get the same sort of answers. The fact that you are "certain" that it can be done is a failing of too many beginner's questions, they ask something they think will be a solution, leaving out the intermediary steps that likely are important to the ultimate solution. You've already gone down a path, without being sure that path is the right one.

Michael

You still haven't told us how much CURRENT the lousy fan draws. Of its over 500 mA (1/2A) it can draw too much current and damage the motherboard. You know WHERE you can put your two cents.

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

coffee warmers, lamps.

Bye. Jasen

Rather than a resistor 3 1N4001 diodes in series will be about right, not that this is necessarily a good idea: if the fan seizes it could damage your computer.

Bye. Jasen

Is it bird walking? Keep your 2 cents and hire a consultant.

I don't know how much current the motor draws. I bought a cheapo battery powered fan from the drug store. It takes 2 AA batteries to power it. That means 3V total and whatever the current of 2 standard AA batteries are. Anyone know what the current would be for 2 AA batteries? There is definitely a solution to this problem because we all know that you can buy a USB powered fan at the store.

Go to the battery manufacturer's web site and look up the AH (Amp Hour) capacity of your model of cells. Get a fresh set of cells, turn on the fan, and see how long it blows before its output is useless. Divide the AH capacity by the # of hours it ran, and that will tell you how many amps of current the fan draws. You might get more life out of the batteries if you turn the fan off for, say, 10 minutes every hour - but be sure and record the "run" time accurately.

Or, you could stick an ammeter in series with the batteries and motor, and measure it. :-)

Good Luck! Rich

Put in fresh batteries and run it until it dies, recording the time it takes to expend the cells OR get yourself a current meter and measure the demand of the fan OR just hook it up and hope for the best.

Case in point, my Sony Vaio laptop powers an external 2.5" hard disk with no trouble at all yet my Dell can't run the same drive without resorting to the external power pack.