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Voltage regulator

Is there an AC voltage regulator that can regulate the voltage to 115 v AC
from a 5000 watt generator turning at between 500 and 4000 rpm’s ?

A 5000 watt generator should be able to deliver 115 VAC at the rpm you mentioned. It may not be stable enough to run an electronic device but should run fans and drills OK. Why the specific rpm?

Not really over the range of stated rpms. The rpms need to be set at a range specific to the motor/generator winding or armature. This is to create the correct 60 cycle ac waveform. You would have to have a very tricky circuit to generate the correct ac wave form over a range of rpms. If the motor were a dc motor this would be a different story, but if its a generator its an ac source.

The several AC generaters that I am familiar with are governed to run at the proper speed for 60 cps +/- and should not be operated unless at the designed speed. From 5 to 40+ horse power the engines all seemed to run in the 3,000 to 3,600 rpm range.

For 60Hz the RPM has to be a sub-multiple, depending on the alternator’s number of poles:
3600, 1800, 1200, 900 rpm etc.
IIRC the alternators at Hoover Dam spin at 150 rpm.

I expect such a thing exists, but I don’t know how you’d go about finding one for sale.

I think that’s is very similar to what a car’s voltage regulator does. It accomplishes the regulation by varying the amount of magnetizing current to the alternator. The alternator has to put out the same voltage independent of the RPM. But you need something different than a car voltage regulator, b/c you want to put out more power and a typical car alternator, and you want to regulate AC, rather than AC Diode converted to DC which is done on cars.