Re: [mowbot] [OT] Driving 6v DC motor with 12v power supply

Dave Everett (deverett nospam at
Tue, 18 May 1999 08:13:15 +1000

At 10:29 17-05-99 -0500, adamdb nospam at wrote:
>Can I drive a 6v DC motor with a 12v battery by using PWM and a 50% (or
>less) duty cycle? How will this affect the life of the motor?
You can, but only if you reduce the frequency and put a low pass filter on
the output. This would effectively turn the PWM signal into a variable
analog voltage.

Having said that, DON'T DO IT! You'd need a substantial power resistor and
would waste energy in heat.

The best choice is to use a 6v battery.

>Is there a rule of thumb for the frequency to use? I was going to use a
>PIC for control and the timer overflow interrupt, thus giving a frequency
>of 4 KHz. Does this seem reasonable or should the frequency be higher or
>lower (in general).

The freq should be much higher. Each motor will have an optimum frequency
and you should try to find it. It will certainly be above audio (4khz is in
the audio range).
>By the way the motors in question are from a kids sidewalk car and I'm
>sure are just standard DC motors (not the newer coreless motors).
They would be standard motors, I have 4 of them here.

If you can tell me why you want to use 12 instead of 6 I may be able to
devise a workaround.

Dave Everett

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