Trouble checking generator hertz

[Bebop367]

Having trouble checking Hertz on 8000 watt generator. Multi Meter will show approx. 59.6 for an instant (sometimes for a few seconds) and then show 179+- Hz and then jump to three hundred range and all over the place.

I checked 5000 watt generator the same way and it holds steady at 60.6 hz. w/no load and about 59.7 with a pretty good load.

Any tips or suggestion would be appreciated.
Thanks

 

[Quest]

put a resistance load on it (300+watts) and then check again.

Q.

 

[Bebop367]

I put three (3) electric heaters with apporx. 3600 watt load and it showed the same.

Could maybe the electric start system affect the meter?
The other 5k generator has no electric start set up.

 

[AandPDan]

The electric starter should not matter. For one thing it's not being used when you're running the generator.

Possible bad connection between your meter and the generator?

Try another meter.

 

[Wheel]

I've seen a wide range of outputs from generators. Electronic devices should have the power conditioned after the output from any generator. Voltage, Hertz and even the waveform have been far out of spec.

 

[Skid]

Sounds like the frequency is fine (around 60 Hz) but that you've got some energy in the odd harmonics (180 Hz = 3 X 60, 300 Hz = 5 X 60). Let me guess. Square wave inverter.

 

[skyactiv]

Find an old non quartz electric clock that relies on 60 hertz for it's accuracy.

 

[eljefino]

Paint its flywheel/ fan in one spot and use an old magnetic ballast T12 flourescent bulb connected to mains voltage to look for a "strobing" effect.

You probably have some sort of extra noise that gets considered a "spike" by your meter.

You could also put a $15 "tiny tach" on the plug wire.

 

[HerrStig]

Originally Posted By: eljefino
Paint its flywheel/ fan in one spot and use an old magnetic ballast T12 flourescent bulb connected to mains voltage to look for a "strobing" effect.

You probably have some sort of extra noise that gets considered a "spike" by your meter.

You could also put a $15 "tiny tach" on the plug wire.
Try a hobby shop for the little tachs used to check model aircraft propeller speed. What you are doing SHOULD work but only if the output of the generator is "clean".

 

[eljefino]

You misread, I'm trying to get the generator spinning at 3600 RPM exactly. I only assume it's output will then be proper.

Since mains voltage is a pretty good 60 hz, it'd be a good source for the "strobe".

 

[HerrStig]

Originally Posted By: eljefino
You misread, I'm trying to get the generator spinning at 3600 RPM exactly. I only assume it's output will then be proper.

Since mains voltage is a pretty good 60 hz, it'd be a good source for the "strobe".
IF it's a two pole alternator. Most are. Using 60 HZ powered lamp is like using a timing light to freeze the flywheel mark at 60 cycles. If the genset uses an inverter, there should be a "don't touch this dial" adjustment for frequency, but inverter outputs can fool a simple counter.

 

[meep]

keep in mind that the engine will probably spin ever so slightly slower under load. The mechanical governors are really pretty good but they aren't perfect. I think anything within a hertz or two would be good. More hertz is also safer than less.

 

[HerrStig]

Originally Posted By: meep
keep in mind that the engine will probably spin ever so slightly slower under load. The mechanical governors are really pretty good but they aren't perfect. I think anything within a hertz or two would be good. More hertz is also safer than less.
I think the waveform is more important than the frequency unless you are running mechanical clocks with it. Transformers designed in Europe for 50 cycles are usually happy on 60, the new one size fits all swtichers work on 50 or 60 and from 100 to 200 volts. Inteesting stuff going on there.

 

[Vikas]

Buy a $15 Kill-A-Watt plug in thingy and forget the other suggestions. I though ElJe would have chimed in with it.

 

[Bebop367]

I got a Digital Photo Tachometer coming to check RPM.

The Vanguard engine has a RPM adjustment screw that should help if RPM are off.

I almost purchased a Kill a Watt Plug but though it would read hertz all over the place also.

 

[meep]

it's the dirty harmonics (smaller, higher frequency wave forms imposed over the primary 60hz waveform) that are throwing the meter. If you put a load on it, like a small heater or a few incandescent bulbs, you may be able to tame the extra harmonics.

 

[Bebop367]

It does stay showing 59.6+- a few seconds longer with a load.

Thanks to everyone for the comments, I know very little about electric power.

If RPM check to be very close to 60 hz., is it safe to assume the power is OK as far portable generator normally produce?

I have run my other 5k generator powering computers, TV's, central heating units etc. for a day or two a few times with no problems. But it does show very close to 60 hz. with the same cheap multi tester.

 

[1 FMF]

post your make/model of generator.

with generators it depends what you run off it whether you will run into problems. and most times the problems are not disasterous like most people think.
- non electronic things like incandescent lights, halogen work lights, will run fine regardless of generator rpm, electrical freq. and voltage. as long as voltage is 120v +/- 20v it's fine, frequency > 50hz.
- induction motors like air compressors, power drills, refigerators, same deal except they draw a high initial current on startup which can blow the generator fuse. but most things like refrigerator or air conditioner... the big motors, have a capacitor to help prevent that. once running, lower voltage than expected 120v and lower freq. than ~55hz is harder on the motor. check your stickers on the motor it'll say voltage range x..x and frequency x hertz to 62 hertz.
- for electronics today it's really a myth. all the power supplies, like the power supply on your computer or flat screen tv, do the "power conditioning" within and like with the motors will have a sticker staying acceptable input voltage/frequency range. I have run personal computers off portable generators a lot and believe me when i say the voltage/frequency is not stable i can hear the generator surging and i've never had a problem. the only practical thing i can think of that somewhat needs stable voltage/frequency are the electronic ballasts of the cfd lights that have been rammed down our throats, those will die much sooner than later, such as http://www.homedepot.com/b/Electrical-Light-Bulbs-CFL-Light-Bulbs/N-5yc1vZbmat

my recommendation would be to put one 500 watt halogen light or equivalent as a load on the generator, have some kind of load, and set your governor so your meter reads around 61 hz. and then check no load frequency and as long as it's less than 62.5 hz your good. this way as generator load increases, or the carburetor goes south they all do, generator speed is not going to increase it's going to decrease. with AC electricity, frequency is also power, it's not just the voltage.

 

[RF Overlord]

Unless your generator is possessed, it can't possibly be making 179 Hz or anything even close to that. The 59.6 is most likely correct and your cheap meter is being fooled by harmonics, as suggested above.

 

[Bebop367]

I got a meter to check and set RPM.
RPM check approx. 3650 with no load and approx. 3585 with approx. 6000 watt load.
Close enough. I think I will quit worrying and let it be.

Thank you all for the suggestion and comments...they were helpful.