Using the lathe is very convenient for me. It’s a 5HP power source that can drive my generator at any speed I care to use.
I hauled a whole bunch of batteries with me, and I wired up that board in advance so I wouldn’t piss around while at work. The planning paid off because I got in, did all the tests, and packed out in 5 hours. I brought my old Wattmeter with me, and it was indispensable. It’s much simpler just reading off that steady needle than trying to decide which of the 3 decimal places to keep on a DMM. Speaking of DMM’s, they actually agreed with each other most of the time, a nice surprise. Just to illustrate and have fun, I ran the current (about 40 amps) through a thin piece of wire (last picture) and made it glow nicely!
The reason for all this stuff is so that I can measure both the input torque and RPM. With those figures I have the input power. With the wattmeter on the output side, the analysis gets pretty simple: efficiency is power_out divided by power_in.
All of the tests used 24V batteries. Maybe I could have tried 48V but I can’t contemplate a 48V system at home right now, so it would be totally academic. The goal of the tests was to size up the prop, and identify the preferred connection scheme for the generator.