Speed Reduction for a DC Motor

Thread Starter

jj_alukkas

Joined Jan 8, 2009
753
I have a Car Radiator Fan motor for 12v DC, 2-wire and pulls 1.5A when unloaded to something near 6A when loaded. I am using it for another project and need to reduce the speed by half. It need not be variable, just a one step reduction to near half the normal speed. Any simple tricks to do it? Can use FET's or anything, but I would prefer to have it built for 10A load. I searched and found only PWM driven variable models, which would not be of much use for my application. How to go with this?
 

iONic

Joined Nov 16, 2007
1,650
Actually PWM is a very efficient way to get your fan down to half speed. With a fixed Duty-Cycle of 50% you will have the fan at half speed.

Waiting to see what your application is though.
 
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Thread Starter

jj_alukkas

Joined Jan 8, 2009
753
Actually PWM is a very efficient way to get you fan down to half speed. With a fixed Duty-Cycle of 50% you will have the fan at half speed.

Waiting to see what your application is though.
So I guess for the simplest pwm, I would need a 555 driving an FET or power transistor?
 

SgtWookie

Joined Jul 17, 2007
22,210
That's basically it, but you will also need a large diode across the motor; or the current going through the motor will have noplace to go when the MOSFET turns off, and it will blast its' way through the MOSFET, killing it.

The diode should be rated for at least as much current as you expect to have going through the motor.
 

THE_RB

Joined Feb 11, 2008
5,438
There are a lot of cheap kits on the market for "DC motor PWM speed controller" you might want to do a google and just buy a $20 kit that will be easy to assemble and reliable.
 
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