PWM in, PWM out (no Sine wave) Please Help [SOLVED]

[Eagle411]

I'm using the Dual Motor Board connected to a 30V supply through a 10ohm resistor. The output isn't connected to a load. I'm measuring the output on my oscilloscope between the motor outputs and the HV battery negative. I'm not getting a sin wave. I'm getting a PWM output, but the duty cycle pulses a little.




I've asked this in another thread, but it wasn't the initial ask. I'm hopeing someone will take pitty on me.

[uhi22]

This is normal from my point of view. In stand-still, all three phase outputs have the identical 50% PWM, so the effective voltage over the motor windings is zero. If the inverter wants to drive a current through the motor windings, it applies slightly different PWM duty cycles to the phases, so that we get a non-zero effective voltage.

If you want to see the sine wave, you must: 1. use a differential probe between the phases, 2. use an additional low-pass-filter to hide the PWM and 3. adjust the oscilloscope to a much slower time interval, to capture a few Hertz instead of kHz.

[Eagle411]

I really appreciate your help!!! Analog and power are two things I haven't done much with, but I'm learning. thanks

[Eagle411]

I did two of the three recommendations and this is the result. Seems more like what I would expect. I hooked the outputs to the motor with no change in the output waveform or current draw (which was 0.01 A). The voltage supply was set to 15V.

[uhi22]

Perfect. If you now add an RC lowpass between the phases and the osci probe, e.g. 4.7kohms and 100nF, the sine wave will be visible.

[arber333]

Perfect. If you now add an RC lowpass between the phases and the osci probe, e.g. 4.7kohms and 100nF, the sine wave will be visible.

Would a trio of incandescent light bulbs be good for that?