Hi.

Using PWM to control a motor has the same affect as lowering the voltage, and I wondered if any one could think of a way of measuring (in the circuit) the 'apparent' voltage - i.e. the voltage that would be needed to make the motor spin at that speed.

Or measure when the duty cycle went beyond a trigger point.

Not for any particular project, just thought process going around in my head.

Cheers,

Tim

 

just measure it with your digital voltmeter, it will give the average voltage

 

oh really? ok, then, but I don't want to know the actual voltage, but I want to measure it with something like an op-amp, to compare the voltage. Would the op-amp measure the average voltage, or would it operate too fast and keep changing?

 

Tim,

[quote=

Using PWM to control a motor has the same affect as lowering the voltage, [/quote]

Actually PWM is much better than lowering the voltage, you get a significantly higher torque from the motor and better control of the rpm.

Ante :roll:

 

at the expense of torque-ripple.

 

Styx,

I did not say it was perfect (even the sun have spots) only much better, and it is!

Tim,

You can set up the op-amp to measure the average voltage if needed.

Ante :roll:

 

using the normal comparator configuration? Or is there extra stuff needed.

Thanks a lot guys!!

 

and i didn't say PWM was bad. In fact it is very good. Only way to control anything with real power and due to it has cause Sycronous machine to start making headway into what was Induction machine areas (nasty things)

 

what you want to do is use a low-pass filter to average out what teh voltage is. You will need to buffer the PWM signal first to stop the low-pass filters imedance messing with the PWM. The cutoff freq of yr low-pass will be based upon what your switching-freq is