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Generac Generators (SEARS, etc.)

Generac voltage problems


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  #1  
Old 12-08-2008, 12:30:56 AM
kphee kphee is offline
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Default Generac voltage problems

I was given a 7 year old Generac 10000 watt generator. When I measure the voltage on the 240 V circuit I get 190 volts at idle which jumps to 300 V at speeds above idle.
I do not know what controls the engine speed, it does not increase when a load is applied. Also what controls the voltage? There are two large capacitors on top of the generator head and I assume this is a brushless unit since I do not see any slip rings and brushes when I opened the end cap of the generator head.
What should I check to fix the engine speed problem and the voltage problem? Are they related?
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Old 12-08-2008, 09:45:41 AM
K D Redd K D Redd is offline
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Default Re: Generac voltage problems

Yes, they are related. I would work on the engines governor system first. Most, but not all of these generator need the engine to run at 3600 RPM to output 60 HZ AC. This would be a 2 pole system. If you by chance have a 4 pole generator, on which the engine only needs to turn 1800 RPM for 60 HZ power, and the engine was turning near 3600 RPM your voltage would be VERY high. You might look at the thread "Wrong info on Onan name plate" on the Onan sub-board for a thread of someone who had a 1800 RPM generator with a governor problem causing the generator to develop to much voltage. There should be a data plate somewhere on your unit giving the RPM of the unit. To many, a small engine running near 1800 RPM's will sound as if it is at idle. Is this engine a GENERAC engine?
With you "At Idle" reading of 190 volts, I would say the RPM that the engine is running then is near what it should be running all of the time.

Kent
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Old 12-08-2008, 11:09:50 AM
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Billy J Shafer Billy J Shafer is offline
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Default Re: Generac voltage problems

You might try going to RV.NET. New guy on the tech form that is a trainer with Generac. He may be your best bet on getting Generac info.
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Old 12-08-2008, 09:15:57 PM
kphee kphee is offline
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Default Re: Generac voltage problems

This Generac has a Robins engine. What I gather from the reply from K D Redd is that the voltage output is tied to the engine speed? So the governor is supposed to maintain a constant RPM at all loads?
If my interpretation is correct then that explains the high voltage when I manually force the engine throttle valve open, so then the no-load idle speed must be set too low since the 240 V outlet is only measuring 190 V at idle.
Thanks Billy I will look into the RV.net forum also.

Ken
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Old 12-08-2008, 09:27:56 PM
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Talking Re: Generac voltage problems

Ken, the thing you need to do is set the Frequency to 62 Hz, with NO Load, by adjusting the rpm at the Governor, and then measure the Voltage. Should be 120 Vac +10% or so. Then Load the Genset to 80% of MAX Load, and check the Frequency, and Voltage again. Frequency should not be lower than 58 Hz, and the Voltage should not sag lower than about 109 Vac. If those parameters are met, then your running just "Spiffy". If NOT, then you need to adjust the Governor, so that it keeps the Output within those Specs. Rpm needs to stay within 58-62 Hz, and this is used to set the Governor, Loaded and Unloaded. The voltage of these units is set by the Design Ratio of the Field to Stator Windings, and is not usually adjustable
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Old 12-08-2008, 10:49:49 PM
kphee kphee is offline
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Default Re: Generac voltage problems

Thanks BTPost, you really cleared up my confusion on how this generator works, I was wondering why I couldn't find a voltage regulator on this unit, now I know!

I have one more question, what do I use to measure the current frequency? Do I need something like a Fluke clamp meter?
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Old 12-09-2008, 12:57:51 AM
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Talking Re: Generac voltage problems

No, you need a Frequency Meter, something like a Kill-a-Watt, or you can use an older electric clock. With the clock, you plug it into the genset and compare it to a clock that uses a Watch Crystal for timekeeping, and time the genset for a Minute. If the electric clock is faster you slow down the genset, or if it is slower you speed up the genset. You can also use an RPM meter and set it for 3600 or 1800 Rpm depending on how your Genend is wound.
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