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Generator high voltage and hertz

  • Thread starter Thread starter Griffweegus
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Griffweegus

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May 24, 2015
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  1. OWNER - I own a Hatteras Yacht
Hatteras Model
68' MOTOR YACHT (1987 - 1987)
Hi Guys,One of my onan generators is putting out 275v and spiking the hertz gauge. Has anyone experienced this? If so, what was the fix?
 
Griffweegus said:
Hi Guys,One of my onan generators is putting out 275v and spiking the hertz gauge. Has anyone experienced this? If so, what was the fix?
Click to expand...
Is the rated output 240v? or 120v? If 240v that might be just a regulator adjustment or fault. The actual voltage can vary with load. Try checking the voltage in a no load status / situation.
 
Hz is controlled by RPM. Sounds like you've got an overspeed problem to start with.
 
Always verify the instrumentation is reading correctly. A decent multi meter will do freq and volts.
 
I have a frequency meter that plugs in to an outlet with a digital readout.

It sounds like there's 2 or more issues.
 
Thanks guys. The gauges are correct. It seems to be an over speed issue. I am gonna work on it this week.
 
Did the Genny suddenly go from working correctly (proper voltage/HZ) to it's present condition? If the RPM is wrong - which, as noted will cause the problem - the difference in the RPM/sound of the engine would be pretty noticeable. And, if it WAS working properly and it IS due to excessive RPM, how did that occur? IOW, the RPM is adjusted mechanically in most cases and it can't just suddenly change.

If it's mechanically adjusted, there is usually a locking nut that prevents the adjusting screw from moving once RPM is set. But even if the lock nut was not tightened, NORMALLY the adjustment screw will unscrew, which will reduce the RPM/voltage/HZ. I've never heard of vibration causing a screw to tighten itself but I suppose anything's possible. ;)

Was work done on the Genny just prior to the problem?
 
Last edited:
Dang, Sky, I'm shocked (NPI)! I can't believe you are using that in lieu of the Marine version. I'm sure WM has them...shouldn't cost more than a hundred bucks! ;)
 
jrbrein said:
Sky,

Will this meter read volts and Hertz from any AC outlet when the generator is supplying power?

Jon
Click to expand...

Yes. But remember, you are only reading one 120v leg.
 
MikeP said:
Dang, Sky, I'm shocked (NPI)! I can't believe you are using that in lieu of the Marine version. I'm sure WM has them...shouldn't cost more than a hundred bucks! ;)
Click to expand...

The boat has it's own meters. I just like that one since it's portable and you don't have to open any boxes or panels to test; just plug it in.

You can also plug a load in like a refrigerator and see how much it draws over time. That comes in handy when figuring amp hours for inverter/battery usage.
 
Sky,

Thanks!
I just ordered one.

Jon
 
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