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UH-OH, here we go again with electricity !

B

Bob Bancroft

Well-known Member
Location
Aurora NY
I'm ready for this next little storm. Got my PTO alternator hooked up to one of the tractors. I test ran it, and decided to check it with the neat electrical monitor which has been discussed on here. My assumption that cycles was a more accurate way than voltage to set the RPM had been confirmed. Well phooey! Lower the RPM to about 110V, and it drops to 50. At any RPM/voltage above that it reads 60. So much for that idea.
 
Bob,

Your regulator is set above 110 so it can sag to that under load, the correct method is get the RPM's right with the frequency. The voltage regulator will control the voltage.
 

Cycles is the ONLY way to set the proper rpm. If the generator had a good quality voltage regulator it would hold 120V at 50,60 and 70Hz.
 
Since I only know enough about this subject to be dangerous, I think I stated my conclusion incorrectly. It's not the theory that disappointed me, it's the meter. I assumed it would show me absolute cycles.
You think my alternator has a voltage regulator? I also assumed since voltage seems to directly correspond to RPM, that RPM was the only "regulator". When I have the alternator running the big fan on a grain bin, I can hear the fan speed up and slow down as I move the throttle around on the tractor. It's like they're hooked directly together as with a PTO shaft.
 
You are "sort of" operating the generator as a VFD when you adjust the RPM, the bad thing is a VFD will keep the voltage up so that amps do not rise.
 
I've got an old Generac 15,000 watt PTO generator. It has a volt-meter and a Hertz meter. Makes around 125 VAC at 60 Hertz cycles. If I rev it to 140 volts, the cycles change along with it. Done that many times by accidentally hitting the throttle. Makes my lights in the house get nice and bright.
 

you adjust the RPM's for the correct frequency. The voltage regulator will take care of the rest. Also measurements taken with no load on the alternator will be somewhat bogus.
 
Some generators have voltage regulators some don't. Speed sets the voltage. I set mine at 62 hertz no load which is around 130 volts. Because both will drop when the load comes in.PTO units are a little different because you have more engine power to run the gen section.With a good meter you should be showing 60-61 hertz. 110-125 at the correct rpm setting.No load.
 
Check your voltage inside the house, running as many loads as possible. You'll probably have a fair amount of voltage drop between the generator and your loads. Also check it at the generator with no load. You probably don't want the no-load voltage to go over 130 volts, nor for the voltage under load to drop below 115.

I assume you're using a Kill-a-Watt meter. Bear in mind these devices aren't real accurate when it comes to reading voltage. You need a "true rms" voltmeter to accurately read the voltage coming out of a generator, and I'm pretty sure the Kill-a-Watt doesn't do TRMS. With a nice clean sine wave off the grid, a peak-averaging meter will accurately read the RMS voltage. But generators typically don't produce clean sine waves, which will cause a peak-averaging meter to read high or low versus TRMS.
 

Of course the AC induction motors vary rpm in proportion to the frequency of the AC power produced by the pto powered AC alternator . Speed the pto Rome up and the output frequency rises.
 
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