Standby Generator < 120V at no load

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  #1  
Old 10-18-14, 05:33 PM
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Standby Generator < 120V at no load

I have a Briggs & Stratton 7KW standby generator, model 40221. At no load, it only produces 115V. Shouldnt it be at 120V at no load? I checked the RPM and its running at 3650 at no load. Frequency using a kill-a-watt shows random fluctuations btwn 59-63 at no load. It wont stay stable at one frequency. Is this normal to have the frequency fluctuate all the time? I cannot find any way to adjust the voltage or the governor. Since the voltage is lower than 120V, when I turn on the microwave, voltage drops to around 108V. Any advice? Thanks.
 
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Old 10-18-14, 05:57 PM
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Welcome to the forums.

Usually at "no load" a generator will sit at 125vac and +/-62 hz. as a rule of thumb.
Is it running AT 3650 RPM or is that drifting too ?
Are you running on natural gas or LPG ?

Your unit has an AVR (automatic voltage regulator) controller.
 
  #3  
Old 10-18-14, 06:27 PM
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Thanks for the prompt response. The RPM is stable at 3650 eventhough the frequency is drifting at no load. I'm only using a Redington tach meter to measure the RPM, so not sure how accurate this is. I'm running on LPG. I dont think this unit has AVR. I looked at the parts list for this model and no AVR is listed, so not sure how it maintains voltage. The wiring diagram in the manual however shows a voltage regulator connected to the stator. Very confusing.
 
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Old 10-18-14, 08:09 PM
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Here is a link for a manual for your unit.
Briggs & Stratton 40221 Installation, Start-up And Operator's Manual

On page 29 it lists 194993GS as an AVR circuit board.
 
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Old 10-19-14, 05:56 AM
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Thanks! Now how did I miss that? Guess I was looking for the words voltage regulator and not AVR!! Given my situation of low voltage and fluctuating frequency, do you think the AVR has gone bad? Any way I can test it?
 
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Old 10-19-14, 07:54 AM
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How does the generator perform under load?
 
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Old 10-19-14, 08:23 AM
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I mainly hook up lights, 1 fridge, 1 freezer and a 1000W microwave to the gen. So, I'm hardly even at 50% of load. During outages, when I use the microwave, it drops to around 108V at the outlet where the microwave is connected to (using a kill-a-watt). I did not get the chance to check the RPM under this situation though. As the microwave load is higher on one of the legs, will the gen adjust the engine speed to compensate or does it only do so when both legs have balanced demand?

My main concern is that the gen only outputs 115V at no load when everything I've read so far suggests it shld be at 120V-125V. At 115V, it does not give it much leeway for voltage drop under load. Or shld the gen auto adjust given its not even at full load?
 

Last edited by klingon888; 10-19-14 at 08:39 AM.
  #8  
Old 10-19-14, 10:26 AM
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The engine should maintain speed regardless of the load on the generator. The engine governor only senses the speed, not the load. If the engine slows the governor increases the throttle to maintain approximately 3600 rpm.

Your governor may not be working correctly.
 
  #9  
Old 10-24-14, 02:08 PM
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Problem Solved .....

For future readers having the same problem....

Thanks to PJmax for the location of the AVR. I replaced it with the new design AVR part# 314338GS, which has a POT to adjust the voltage. Old AVR didn't. First step after replacement was to adjust the freq to 62-62.5 Hz, 3750 RPM, then adjust the POT clock-wise to increase voltage to about 123VAC per the instructions. Problem solved!
 
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