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Topic: voltage variance on generator (Read 865 times) previous topic - next topic

voltage variance on generator

I was working on the coach today. I had the 10kw generator running with two air conditioners and 20 amp power share on the charger. I saw about a 5 volt variance in the voltage. It was just a rhythm change. Do I have a problem?
Jerry & Joanne       
'95 40' U320c SE Foretravel
towed '11 Jeep Liberty
Green Valley AZ.

Re: voltage variance on generator

Reply #1 –
I have been researching this issue and found this previous post.  My generator RPM also oscillates under load.  Under minimal load up to and including A/C fans the Generator RPM and Voltage is steady, as soon as one of the A/C compressors comes on, the RPM starts to oscillate.  The voltage change is about 5 volts and the cyclic rate is about 1 Hz.
I am assuming it is a lack of dampning in the governor linkage, such as wear in one or more components.  I am going to look at it tomorrow and was hoping someone might have some insight.
Steve DeLange
2005 U320T 40'
Pearland, Texas

Re: voltage variance on generator

Reply #2 –
After running generator with the cover open this afternoon, it doesn't appear the RPM is fluctuating. The oscillating sound appears to be the A/C compressors and fans fluctuating under a variable voltage situation. With only the fans running the voltage is a steady 120v. When either or both compressors run, the voltage oscillates about 3v. The oscillating sound is slight but noticeable when there is no other noise in the cabin.  It may be more noticeable in the rear.  Is this a voltage regulator problem or is the generator breaking down under load?  Any suggestions?
Steve DeLange
2005 U320T 40'
Pearland, Texas

Re: voltage variance on generator

Reply #3 –
I think what y ou are noticing/hearing is the difference between the generator rpm and the compressor rpm, the difference is called "Slip".  When you look at a electric motor, the rpm will never be 1800 rpm like most generators, but 1725 rpm seems to be a popular rpm.
What you hear is the in and out of phase between the two rotating units.  Like a twin engine airplane or twin engined boat, unless the engines are running exactly the same rpm, you have the same sound of in and out of  phase.
Nothing new here, as for the 3 volts, relax, sounds well within normal range, very few generator regulators will maintain a perfect steady voltage setting, only the most expensive type, same with the governor, our units have a mechanical governor,k they depend on droop to maintain speed, without being over sensitive and surge up/down.
I would say relax and enjoy and not be tooooo picky ;D

Re: voltage variance on generator

Reply #4 –
1.25 Hz sound you hear from an out of sync condition between the generator and a compressor would be most noticeable if you stood between the generator and the first compressor.  The sound I am hearing is more noticeable the further aft you go in the cabin.  I determined my generator RPM is steady.  I agree a voltage dip of 3-5 volts is not significant, however an oscillation of 3-5 volts indicates an unstable situation either a regulator or possibly a generator.  Contacted Powertech again and they suspect the exciter may be loose.  Looks like I get to disassemble the generator.
Steve DeLange
2005 U320T 40'
Pearland, Texas