Portable generator voltage question

[General Lee]

I have a briggs&stratton 5500w portable genny. I was testing some things the other day and noticed the unit is putting out 129.8 volts with NO LOAD. I hooked up a small box fan and. Shop vac and the volts dropped to 121.

Is it fairly. Normal to have high volts with no load? The unit is in excellent shape (bought new) and has about 125 hours or less on it.

 

[Gregishome]

Yep, better to be a little high than low as it still in the 5% allowance. My 5500 watt Generac does the same thing.

 

[General Lee]

Cool that makes me Feel a little better. For some reason Though my ceiling fans dont like the power from my generator. Even running under capacity with the genny they hum when used so I don't use them. When I noticed the high voltage I thought that may have had something to do with it.

 

[rlitman]

No, the hum is from harmonic distortion, not overvoltage.
Your voltage sounds spot on.

 

[Gooch]

Cool that makes me Feel a little better. For some reason Though my ceiling fans dont like the power from my generator. Even running under capacity with the genny they hum when used so I don't use them. When I noticed the high voltage I thought that may have had something to do with it.

The hum is from not having a clean 60hz AC frequency.(IIRC less, higher overheats them IIRC) Also avoid plugging anything electronic into them(tv, computers, dvd players, even refridgerators have electronics in them now, but in a extended power outage, you'll plug this in.)

 

[ddawg16]

Something to consider.....what kind of meter where you using? The cheapo's are not true RMS meters....so, if your generator output has any harmonics, it could make the reading be higher than it really is.

RMS means Root Mean Square. If you look at the sine wave of your AC power, the actual peak is 1.7 x the RMS....

I would be interested to see what the actual generator part of your generator is....I have always thought they were a simple AC generator...no real electronics...other than the regulator that tries to keep the engine running at the right RPM's. Maybe they are using a DC generator....dumping that output into a DC to AC converter...in which case, your going to have harmonics.

If you are concerned about harmonics, you can get simple line filters....basically, they are transformer chokes...kind of expensive (heavy copper)...but simple and reliable.

 

[rlitman]

Ok, at work I deal with harmonics in generator systems on a kind of regular basis, but it's all three phase. Some things stay the same in single phase, some change.

Anyway, no, a line filter can remove RFI noise, but will not help with THD, UNLESS you have a filter at each source of noise, tuned to the exact type of noise, OR an astronomically expensive "active" harmonic filter.

Straight out of the generator, you are likely to have high amounts of 5th and 7th harmonic, if you have a 2/3 pitch winding (like most generators), and pretty low 3rd harmonic.
But the biggest source of harmonics in your system is from the equipment you have connected to it. Fluorescent lighting for example, tends to have a high harmonic current.

Now, if you have an inverter generator, you essentially have an active harmonic filter already. The inverter will control the output voltage and will eat up a large amount of the harmonic content. Kinda neat, heh?

 

[General Lee]

Sheww, ddawg- I know the basics when it comes to electrical but the stuff your mentioning makes my head spin lol. The volt meter I'm using wasn't to cheap of a model, 30 or 40 bucks but I don't have name brand handy at the moment.

Gooch- given that it's not a top of the line generator I'm sure it isn't putting out the cleanest frequency or electricity. Knock wood, after using it in 2 or three outages totalling 8 days without power, my electronics had no ill effect. It do something to my microwave though. It was old so either it was a coincidence of old age or improper current burned it up.

I'm actually researching and shopping for a bigger genny or a whole house option. Using this portable or any for that matter makes me nervous about damaging whatever it's powering.