openinverter forum

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.

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.

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

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.

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.

uhi22 wrote: ↑Wed Feb 25, 2026 5:56 am 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?