I just changed my governor control board on my Kohler 5.5 KCM21 genset because the genset was running at max throttle. The new board fixed that problem and the genset engines idles down as it should. I went to try it with a load on but noticed that my old Magnetec battery charger which never charges above 13.3 v read 15.5 v. I read 120 vac in the outlet. I borrowed my friend's meter which measures HZ and volts. It just beeped and a fault light came on for HF( high frequency). I have three questions 1, Why does the battery charger read higher? 2, Can something other than the governor board cause this HF? The board is suppose to come from the factory preset, but it does have three pots that can be adjusted. 3, Or is this just normal and new boards need to be adjusted when first installed. I did turn off the circuit breakers for everything except the lights and converter before testing so hopefully there was no damage except my batteries being equalized.

Freq is too high because the engine speed is probably too high. I would talk to the factory rep and see what one of those pots controls engine speed. I am not an expert and my advice is, as they say, worth what you paid for it. Good luck.

If the frequency is high, so is the voltage. A frequency error won't fool a charger into excess output. Find a real meter that can read a wider frequency band and see what's really going on. We use those Kohlers in news vans and they simply die of old age.

SCVJeff wrote:If the frequency is high, so is the voltage. A frequency error won't fool a charger into excess output. Find a real meter that can read a wider frequency band and see what's really going on. We use those Kohlers in news vans and they simply die of old age. That is what I have always thought. But I checked it with two different meters and both read 120 vac. Also same two meters also read 120 vac when plugged into shore power and 60 hz on the meter. I tried readjusting the carb both main and idle jets but rpm stayed the same. Makes sense it rpm is high the voltage would be high but it is not.

What does the charger do when on shore power? There is always the possibility that the old Magnetec charger is having problems also.Since you don't have a frequency meter you can use a digital clock to check frequency but it might take an hour or so to show an error. A basic digital clock uses 60 Hz power as the timer. If the frequency is too high the clock will gain time. The clock on the coach microwave oven would work for this test. What I can't remember is how much error a 1 Hz change will cause.

electronic Automatic voltage regulation on the field will control the voltage even if the frequency is offHigh Freq does not mean high voltage when you have AVRGjac wrote:SCVJeff wrote:If the frequency is high, so is the voltage. A frequency error won't fool a charger into excess output. Find a real meter that can read a wider frequency band and see what's really going on. We use those Kohlers in news vans and they simply die of old age. That is what I have always thought. But I checked it with two different meters and both read 120 vac. Also same two meters also read 120 vac when plugged into shore power and 60 hz on the meter. I tried readjusting the carb both main and idle jets but rpm stayed the same. Makes sense it rpm is high the voltage would be high but it is not.

High frequency on generator | Good Sam Community

15 Replies

Gjac
Explorer III
Aug 03, 2015
DrewE wrote:
The Magnetek charger/converter might be a ferro-resonant design, which provides decent inherent voltage regulation but is quite frequency sensitive (higher frequencies leading to higher output voltage). Magnetek made a bewildering array of converters of various designs.
Yes they call it a ferrostat in the brochure that I have so it must be what you are talking about.
DrewE
Explorer II
Aug 03, 2015
The Magnetek charger/converter might be a ferro-resonant design, which provides decent inherent voltage regulation but is quite frequency sensitive (higher frequencies leading to higher output voltage). Magnetek made a bewildering array of converters of various designs.
Gjac
Explorer III
Aug 03, 2015
Called parts for tech this morning they were closed all WE, and talked to Dennis their tech and he said the board should have come from the factory preset. Long story short I tried adjusting one of the 3 pots(overspeed) and was able to bring the hertz back down to 60 HZ. Also my old Magnatec battery charger came back to 13.3 v. Dennis did not know nor do I know why the charger would go from 13.3 v to 15.5 v with a higher frequency while AC voltage remained at 120 v other than it must be frequency sensitive. I had to turn the pot several turns to bring the frequency down to 60 HZ.
Gjac
Explorer III
Aug 02, 2015
SCVJeff wrote:
Been a long time because when they really broke, out they came. What I do remember is that we built an analog dual voltage/ frequency meter set to adjust those things.

Gjac: again it's been awhile, but look for a rod with a spring on the end and about 2" of threaded Rod. That's where you need to make throttle edjustments. The old Onan's were very similar.
Jeff I think you are describing a manual governor spring like on a lawn mower, my Kohler has an electronic governor which consists of a magnetic pickup, a stepper motor and a control board to control the rpms based on the load.
MrWizard
Moderator
Aug 02, 2015
where the AVR is located depends on the generator builder

but yes Kolher could have put it on the govenor board

total integration , everything on one board,
and you have to replace a more expensive part when it fails

it cheaper for the MFG to have one board than three boards,
lower total production parts faster assembly lower labor cost , less parts to keep in stock
but it cost the customer more when its time to make a repair
cbr46
Explorer
Aug 02, 2015
Have you checked the manual?
campkahler.com/files/kohler-7cm21-rv-service-manual.pdf

Oddly, this forum is mirrored at formus.goodsamclub.com (yes, I get the corporate connection)

Best,
- bob
Gjac
Explorer III
Aug 02, 2015
MrWizard wrote:
electronic Automatic voltage regulation on the field will control the voltage even if the frequency is off
High Freq does not mean high voltage when you have AVR

Gjac wrote:
SCVJeff wrote:
If the frequency is high, so is the voltage. A frequency error won't fool a charger into excess output. Find a real meter that can read a wider frequency band and see what's really going on. We use those Kohlers in news vans and they simply die of old age.
That is what I have always thought. But I checked it with two different meters and both read 120 vac. Also same two meters also read 120 vac when plugged into shore power and 60 hz on the meter. I tried readjusting the carb both main and idle jets but rpm stayed the same. Makes sense it rpm is high the voltage would be high but it is not.
. Should this HF cause the high charge voltage? Is the AVR on the governor control board?
Gjac
Explorer III
Aug 02, 2015
Dale.Traveling wrote:
What does the charger do when on shore power? There is always the possibility that the old Magnetec charger is having problems also.

Since you don't have a frequency meter you can use a digital clock to check frequency but it might take an hour or so to show an error. A basic digital clock uses 60 Hz power as the timer. If the frequency is too high the clock will gain time. The clock on the coach microwave oven would work for this test. What I can't remember is how much error a 1 Hz change will cause.
Like I said in the 0P the Magnetek charger has always charged at 13.3 V on shore power when running on the generator it charges at 15.5 V. I do have a meter that measures between 60-80 HZ. I get an error code saying HF which means it is more than 80 HZ.
MountainAir05
Explorer II
Aug 01, 2015
best picture that I could fine.

https://www.cumminsonan.com/www/pdf/manuals/940-0502.pdf
SCVJeff
Explorer
Aug 01, 2015
Been a long time because when they really broke, out they came. What I do remember is that we built an analog dual voltage/ frequency meter set to adjust those things.

Gjac: again it's been awhile, but look for a rod with a spring on the end and about 2" of threaded Rod. That's where you need to make throttle edjustments. The old Onan's were very similar.

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High frequency on generator

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