# Understanding stepper motor as generator Vs DC motor (RMS to equivalent DC)

I am using a stepper motor as a generator in a proof of concept experiment for something. The motor came from an old printer so do not have specs for it, but I believe it's unipolar. It has 5 wires, one of which appears to be common to the other 4. That is, there is 80 ohms from this common to the other 4, and 160 between any other 2 leads. I drove it with a DC motor to view the outouts of all channels, shown below. Waveform is a bit jagged I think due to a slight vibration in the coupling

I have previously used a DC brushed motor and want to compare outputs, DC vs AC. My first question is, are the following calculations/conclusions correct?

So, here is the outout of the actual experiment:

I have each of the 4 coils driving an 80 ohm load (a resistor) and get this outout (just showing 2 channels) , giving a 10v peak to peak sinewave. To convert this to the equivalent DC I calculate RMS, which for a sinewave is Vpeak * 0.707 (or 1 over squareroot 2) which works out at 3.5V and power = (3.5V*3.5V)/80R = 0.15W

So, is my 10V peak to peak sinewave generating the same power as a 3.5V DC supply would, for example will it heat up the resistor the same amount?

Second question is, as I have 4 coils, can I say the motor is generating 0.6 W? Without going into details, I assume it is possible to combine the 4 out of phase outputs into one?

• I just read this: A Generator built from a Stepper Motor and Supercapacitors youtube.com/watch?v=1QK6zRQ8D4A Commented Jul 28, 2022 at 14:55