I'm dismayed to see it's nearly a year since the last post, but some minor progress has been made. I have spun the generator up to about 4600 rpm and measured output voltages and currents for a few loads, along with the torque to turn it. I'd like to spin it faster but my poor old pre-war lathe complains too much!
At this speed it generates about 20 V, so I may settle for a nominal 18 V system rather than the 24 V I had hoped.
I am waiting for a high power rheostat from HK to take some higher power measurements, but at around 30 W output I'm getting an electrical x mechanical efficiency of at least 45% when acting as a generator, with a trend for better efficiency as the power levels increase, up nearer to 60%. I'm pretty pleased with these figures.
At worst I will need a mechanical power input of 65/0.45 = 145 W. Equating to 0.2 HP, this should be readily available from the engines through the gearbox. I can keep you posted as and when I get more data.
Regards, Tim