Re: [CAD_CAM_EDM_DRO] Re: PWM Back Emf

Hi Frank,

We run small DC motors for peristaltic pumps, we are able to measure the
back EMF during a specific off time for the motor. We of course have a
uP doing a lot of other things at the same time, and the emf is read
during a slice of time.

Alan KM6VV

Frank wrote:

> I understand the theory you are describing - detecting a change in
> current implies a change in load and a change in speed, so change
> the PWM voltage to compensate.
>
> However, when I start the motor the current hits about 100mA before
> the motor starts spinning. When it spins the current drops to
> 80mA. Once spinning I can reduce the PWM duty cycle so the current
> is about 30mA and the motor is still spinning slowly. Don't I need
> to be at a known speed/load balance point before applying the
> compensations? I can't just say 50mA represents 10% speed because
> my motor will not have started spinning.
>
> Of course all my logic could be wrong because I am testing with an
> unloaded motor.
>