PTO generator/volts vs hertz

[Hughman]

PG&E provided me with an opportunity to exercise my generator and transfer switch a couple of weeks ago courtesy of a 6 hour outage. The transfer switch and generator operated flawlessly. The only blip I heard from the tractor was when I kicked on the well pump (800' deep).

Question I have is which is more important, volts or hertz? When I hook up a meter to one leg I read 115v @ 60hz.

 

[Hughman]

If I bump the tractor rpm up a bit I get 120v @ 61.5hz.

My primary concern is the well pump.

 

[techman]

Not easy to say which is more important. Many devices can tolerate deviations in Hz, including motors, lights, heating devices and most electronics. Voltage can cause some issues. Too high can potentially damage some devices and very low can result in motor issues. If you keep the voltage around 120 and Hz are off a few you should have no problems.

 

[workinonit]

One is no more or less important than the other. Voltage can deviate based on the amount and types of VAR loads you are running. Frequency deviates based on how good your tractor governor is when kW load is added and removed. In larger generators voltage and frequency can be controlled separately. Our smaller gensets don't have that capability so we have to find a happy medium. Generally speaking if you control frequency to 60 Hz voltage will be in a safe band.

 

[steve tym]

As Hz go up, the speed of the motor will go up and the amps will go up. At some point over heating the motor. Both are important.

 

[DarkBlack]

As Hz go up, the speed of the motor will go up and the amps will go up. At some point over heating the motor. Both are important.

That’s incorrect. At a given voltage, AC motors draw more current (amps) and can potentially overheat when the power frequency is below specified. You have it backwards

 

[ponytug]

PG&E provided me with an opportunity to exercise my generator and transfer switch a couple of weeks ago courtesy of a 6 hour outage. The transfer switch and generator operated flawlessly. The only blip I heard from the tractor was when I kicked on the well pump (800' deep).

Question I have is which is more important, volts or hertz? When I hook up a meter to one leg I read 115v @ 60hz.

One point about the legs. US split phase has two hots and a neutral. Hot to hot should be close to 240VAC, perhaps a bit above if you have a long cord to the house to get 240 in the house. Depending on the generator, it may or may not have a great ability to keep the hot to hot at 240 and simultaneously keep each of the two hot to neutral voltages at 120VAC. So, next time, I would make start by making six voltage measurements with no load, and then again with loads on both hots;

• Hot to hot
• Hot #1 to neutral
• Hot #2 to neutral
• Neutral to ground voltage
• Hot #1 to ground
• Hot #2 to ground

Ideally, use multiple meters to measure both hot legs at the same time. You may have measured the voltage on a heavily loaded leg, while the other leg was lightly loaded.

Frequency (Hz) is straight up what the tractor spins the PTO and generator at.

You might look into your PTO generator voltage regulation a bit, if you are up to it. Many generators have ways to adjust the voltage, some of them very readily from the control panel, some not so readily.

All the best,

Peter

 

[RjCorazza]

I'm not as electrically savvy as most of you, but my old Onan 1800 rpm RV generator was adjusted soley to the hertz (60hz here in the States), and there was an acceptable voltage range listed. It's been a long time ago, but I recall 110v being the lower acceptable voltage. Certainly not gospel, but that's what the OEM recommended.
Anyway, I adjust my PTO generator to 60hz while under load and the voltage is always in a reasonable range. The tractor grunts a little when the big loads turn on, but the voltage and hertz remain relatively stable.

 

[etpm]

Here's the way induction motors work: when the voltage drops the motor slows so then the motor will draw more current, amps, in an effort to speed up. This extra current causes heating in the motor windings. If the voltage stays low for a long time, and if the power supply can supply enough current, the motor will overheat. This is why refrigerators will burn out compressors during a brownout, when the voltage drops too much. Frequency variations of 5 Hz up or down will not hurt an induction motor. But low voltage can. That said, 115 volts is OK. Modern motors, motors made in the last 60 years or so, maybe even longer, are made to operate properly anywhere from 110 volts to 125 volts. This is because of the variation in the supplied voltage from the power producers.
Eric

 

[garry1p]

Both HZ and voltage are important.
The power company holds HZ to +/- 1% for a reason and voltage +/- 5%.

Rule of thumb for a generator acceptable voltage fluctuation low 114VAC maximum 126VAC frequency 59.5/60.5
An air conditioner will burn itself up at voltage below 108V very quickly due to over heating when AC is over 136VAC motor and compressor will be toast in very short order.
Same with frequency to high and electric motors run to fast, to low motor runs to slow both cause overheating.