" Now....Before I attached the second steel plate I decided to run some tests. I connected the leads from the rectifiers to a 12 V 12 AH gel battery as well as a 200 watt Inverter. I hooked a 40 watt cd player and 60 watt light buld (total 100 watts) and checked my battery levels with a voltmeter. Within a minute or so, the battery voltage started to drop, so I tried to increase the speed of the ac motor. I noticed that the rpms on the genny didn't increase, but the torque did. In other words the ac motor kept turning the shaft at about 120 rpm. It could not go any faster, but it was turning with a lot more torque. I noticed that the battery was charging steadily even though I was extracting 100 watts from it, to power the cd player and the 60 watt light bulb. "
I wouldn't take the 40w of the cd player as an accurate figure but that doesn't matter.
I assume this is a standard ac induction motor but am not sure if it is single phase or 3 phase. In either case these motors are not suited to variable speed operation with reduced voltage and if single phase then I am a bit surprised that it works at all unless it is a fixed capacitor machine, if it was capacitor start then the starting switch would hold the starting capacitor in circuit and this may work at such low voltage but normally it would blow the capacitor.
Your alternator is doing exactly the same to your drive motor as it would do to the turbine prop. With such a big alternator and reasonably high efficiency the thing just wants to run at constant speed above battery cut in volts. Any attempt to raise the speed will just push more amps into the battery so the power input will go up basically as the current, with little rise in speed or volts.
Your motor ( unless fitted with some gearbox) will want to run at some much higher speed depending on the number of poles and you will be running it in stall below pull out point on its normal characteristic. It will never develop more than a fraction of its full load torque and it will only develop a tiny fraction of its half HP even though you are grossly overloading it.
Probably the nominal 100W you got out of the alternator is pretty reasonable under those conditions. You could hand crank it at that speed with significantly more hp than your motor can produce stalled.
If you try with the second disc in place then your motor will stall even more and you will have even less in the way of power out at the lower speed.
It seems as though your alternator is fine but testing with an induction motor on reduced volts is not very practical. Even with some other type of motor that doesn't pull out and stall you will only get a small % of the rated hp if you run it at reduced speed. If intended for 1500rpm and you run it at 150 rpm you will reduce the hp to 1/10. In reality you have done very well but the motor will be grossly overloaded and hence the thermal trip has operated.
Flux
