I honestly can't remember much about my college circuits class, but I am attempting a small project anyways.

I have a very small 1.5V motor with a tiny 0.5in fan attached to it. as of right now it is just being powered by a single AAA battery. The only thing between the two is a switch. I want to be able to slow the fan down, either permanently or by some means in which I can adjust it's speed. I was wondering what type of resistor or other component might I use for this. I'm looking for specifics ,i.e ohms?, watts?, tolerance? I don't remember what all these mean, but I would like to reduce the fan speed by about 20-30% if possible. OR even better would be something that lets em adjust the speed of the motor. (I also am trying to keep this as compact as possible, so smaller the component the better)

Any help is much appreciated.
Thanks

Liam

 

Have you got any idea what current is taken by the motor at the moment?

I guess that it is about 0.2A but that could be a long way out. It is based on an upper limit of what an AAA can produce and the lower limit of what you would actually want to slow down. Measure it for a more accurate first try.

If that is the case, you would want to drop the voltage to about 1V so you would need (1.5V - 1V) / 0.2A = 2.5 hm:

The power would only need to be 0.5 V * 0.2 A = 0.25W but it would be a good idea to have a 1/2 W resistor.

It is difficult to adjust the voltage when it is that small except by having several different value resistors.

 

Thanks for the info.

I'm not sure what the amperage is on the motor. This is me trying to modify something I got outta a box. It's a real tiny motor(0.45inX0.3inX0.5in). I want to reduce the rpms, so as to quiet the fan down.

 

if I bought two 1/2 watt 1 ohm resistors, would that be a safe starting point? I could wire in the one, see how it works, then step up to the other. I'm willing to spend a little money on trial and error.

 

correction. i meant two 10 ohm resistors.

 

wait. i think i'm wrong again. i went to radioshack's website and couldn't find resistors that meet my requirements. you say try 2.5 ohms, but i can't find anything smaller than 10 ohms.

did you mean 25 ohms?
is there a difference between ohms and Ohms?

I need a little more help here. sorry.

 

There's no difference between ohms and Ohms.

Small resistors below 10 ohms are not common but are available from suppliers such as Digi-Key or Mouser

You can parallel connect four 10 ohm resistors to get 2.5 ohms.

You could also use an adjustable resistor. Radio Shack sells a 25 ohm 3w rheostat (RadioShack.com - Cables, Parts & Connectors: Component parts: Pots, trimmers & thermistors: 25-Ohm 3-Watt Rheostat), which would probably do what you need if it's not too physically large.

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Carl

 

ok. i think i figured it out. dusted off an old physics book from college. I forgot all about the difference between running to resistors in parallel and running them in series.

If i run four 10ohm resistors in parallel i'll get them equivaent 2.5 ohms required. i think.

 

I have a little fan with flexible rubber blades. It is dead quiet. It uses two AAA cells which last about 45 minutes (Ni-MH rechargeable). It draws about 1A.

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Uncle $crooge

 

You could try 2.4 ohm or 2.7 ohm resistors, in either 0.25W or 0.5W sizes, for this circuit.

 

OP says resistors less than 10 ohms are not available to him. This is why the suggestion to use several 10 ohm resistors in parallel.