Offgridder
My 20kw Generac 3600 RPM generator is running over and under speed by approximately 80 RPMs. Fluctuates continuously on RPMs. It is producing between 146 and 148 volts on each leg instead of 120-125 volts. Would appreciate any information anyone can provide on how to fix! Thank you.
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Peddler
post a SN
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Offgridder
What is a SN?
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Geoff Z
serial number
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Offgridder
Serial number is 5737236 model number is 005-7440
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MacL
Sounds like you have a bad voltage regulator (0F97190SRV).  It is putting out 300 volts, which puts a load on the engine itself with increased magnetic resistance.  Do not allow the switch to transfer until the AVR is replaced to protect appliances and electronics inside the house.  I'd leave the entire unit off and open the main circuit breaker until it is repaired.

When you get the new regulator installed, use the pot on the AVR to adjust the no load voltage to 247-250 volts.
State your problem, not your diagnosis.
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Offgridder
Thank you! I was thinking either the voltage regulator or the stator or both. Makes sense that the voltage regulator is  passing high voltage. Can the voltage regulator be adjusted down? FYI - I have 730 hours on the unit. Is there a simple way to measure voltage coming from the stator to the voltage regulator?
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MacL
You can measure leg to leg at the circuit  breaker on the generator through the screwdriver holes, or across the bottom front lugs on the transfer contactor.  

Once a regulator bites the dust and goes to full output or no output due to internal damage, the adjustment doesn't work any longer.  You're welcome to try.  I always do in case someone turned it that high.  And then I find that turning the screw does little or nothing.

But on the off chance you could get it down to 250, you'd want to observe the voltage over time, looking for spikes, dips.  And if the regulator has failed, not only is the voltage high but it probably also unstable



I don't think you could adjust a good regulator up to 300 volts.  
State your problem, not your diagnosis.
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Offgridder
Your diagnosis is dead on! I turned the generator on today after giving it a breather for a couple of days and low and behold voltage was perfect across both legs. After about 15 minutes though bingo! it's spiked back to 146 to 148 volts per leg. I'll order the AVR today.  Thank you again!
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MacL
This has to be the only website where people actually get the answer they seek.  You're welcome.

Obviously the controller doesn't have over-voltage sensing and probably not undervoltage sensing so do check the output of your generator at least every six months, if you have a meter.  

Of course move the wires "one at a time" and install the new AVR with the all the wires already attached to it.
State your problem, not your diagnosis.
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Offgridder
I installed the new AVR successfully and adjusted the pot but unfortunately I'm not getting duplicate readings on both legs. Leg one reads 120 volts but leg two is 25 volts lower at 95 volts. When I adjust the pot up, leg one maintains a voltage gap of 25 volts relative to leg two... (leg one @125 volts : leg two @100 volts) Any ideas on what could be the culprit? Thank you again!
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UPS
Offgridder wrote:
I installed the new AVR successfully and adjusted the pot but unfortunately I'm not getting duplicate readings on both legs. Leg one reads 120 volts but leg two is 25 volts lower at 95 volts. When I adjust the pot up, leg one maintains a voltage gap of 25 volts relative to leg two... (leg one @125 volts : leg two @100 volts) Any ideas on what could be the culprit? Thank you again!
 
Are you checking the voltages with a load on the unit?
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Offgridder
No, just at the breaker with the breaker on and no load attached.
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MacL
What is the voltage leg to leg?  Should be about 248.

  Sounds like there is some corrosion at a test point.  Are you measuring on the line side of the breaker?  If you are measuring on the load side (output side) of the breaker the breaker could have internal high resistance.  Or maybe the neutral connection is loose, where wire 22 & 33 are connected together.  Voltage drop testing across suspect points should reveal the culprit.  
State your problem, not your diagnosis.
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Offgridder
Not sure how to measure voltage leg to leg. 
I just finished retightening all set screws/connections & reseated all connectors/plugs.  During the process I found the 100 amp breaker lug screw for leg 2 was seized in the breaker. The slot in the lug screw stripped while removing it so I fabricated a new stainless lug screw from a bolt which worked perfectly.  Then I noticed the #4 ground wire connector sleave inbound from my solar system to the generator ground was melted and the ground wire had a slight carbon coating (signs of arching) .  I traced it back to the solar and all was nominal there.  Looks like I took a lightning strike at some point in the past!  The ground connector at the geni was ever so slightly corroded, just a light film really.  This was apparently enough for the lightning current to arc. I cleaned it up and reconnected good and tight. I will have the geni ready to test in a couple hours and will update after.
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Peddler
How is your solar system tied in?  I have never seen a ground from a solar panel system tied back to the generator.  The solar electrical system has to be isolated from the generator so that it is off when the utility is off and can't feed back into the generator.  Others with more experience with this should contribute but I fear you may have a problem. 
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Offgridder
The solar install is off grid and has been working nominally for 14 years. There is no grid tie to a utility. Wiring is as required to tie the generator into the system for battery charging and pass-through power to the residence. The wiring is to spec and has been in operation for 7 years There are no issues there. All grounds in the system terminate at the 40-foot x 1-foot diameter steel sleeve of my water well.  All systems are fully grounded and protected. Anyways the issue is with the voltage on leg 2 being 25 volts low.  I have not been able to test due to a heavy rainstorm. Soon as it passes I'll put the meter on it and see how it looks now that all the connections are reseated.
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