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Old 09-18-2020, 10:57 AM   #1
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40Hz to 60Hz Generator frequency

Hi Guys.

I have an Onan 6.5 kW LPG generator which is running nicely. It run exactly at 1800 rpm and it produces also 120V.

Now I have an inverter (Xantrex Freedom 2000W) which also works like a charm. The problem is when I try to charge the batteries with the generator the inverter will not 'accept' the current as it reads 40Hz coming from the generator at 120V (on the display). I have yet to measure the wave with an oscilloscope.

They funny thing is when I turn my rear A/C on and put load on the generator you can hear the generator putting on load, RPM stay around 1800 but now the magic happens: the Inverter reads now 60Hz from the Generator and 'accepts' the signal. Hence it charges batteries.

I don't want to always run a heavy load to have the batteries charged so any clue what can cause this weird phenomena?

Again the RPM is OK. No drops or overshoots, voltage reads OK. Just needs significant load to get to 60Hz otherwise 40Hz.
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Old 09-18-2020, 11:16 AM   #2
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It sounds like your tach is in error, or your generator idles at 1800 RPM. According to what I found, is that at idle, your generator puts out 40 Hz, and at full throttle, 2880 RPM, puts out between 58 and 62 Hz. So, apparently, with your inverter on, and nothing else, the generator isn't sensing a load, and is staying at idle.
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Old 09-18-2020, 01:58 PM   #3
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Quote:
Originally Posted by HarryStone View Post
It sounds like your tach is in error, or your generator idles at 1800 RPM. According to what I found, is that at idle, your generator puts out 40 Hz, and at full throttle, 2880 RPM, puts out between 58 and 62 Hz. So, apparently, with your inverter on, and nothing else, the generator isn't sensing a load, and is staying at idle.
Hey that's an interesting thought which I will test today. I have a buddy coming over so we can test a few more things like signals with the oscilloscope.

Maybe we test your hypnosis first: Check RPM at Idle and at load look if there is linear correlation with the frequency.

Even if this is the case I'm in trouble because it is a chicken-egg story. The Inverter does not take the signal when not at 58-62 hertz, gen set does not make 60 hertz unless there is a draw.

Don't want to have to put a big resistor somewhere just to trigger this
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Old 09-18-2020, 02:11 PM   #4
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Well, that's about a worthless generator. How much load does it need to change to 60 Hz? How do you think small AC motors feel about that 40 Hz? Would a residential fridge even start or kick the generator up to speed?


For the OP: If you start the A/C and now the inverter becomes happy, can you turn off the A/C and the inverter load be enough to continue charging?
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Old 09-18-2020, 02:52 PM   #5
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Originally Posted by tfryman View Post
Well, that's about a worthless generator. How much load does it need to change to 60 Hz? How do you think small AC motors feel about that 40 Hz? Would a residential fridge even start or kick the generator up to speed?


For the OP: If you start the A/C and now the inverter becomes happy, can you turn off the A/C and the inverter load be enough to continue charging?
Ha, yes that is the first thing I tried but it switches back to 40Hz on the inverter display hence kicking off the signal again.
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Old 09-18-2020, 03:25 PM   #6
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You don't say what year your unit is but on the new ones the engine turn 2880 RPMs.

The generator head is belt driven to 3600 RPMs for 60 HZs.

They don't idle at all, only inverter style generators idle. They run at constant speed. What your hearing is the load changing the sound.

Read the specs of your unit to see what constant speed the engine should run.
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Old 09-18-2020, 04:28 PM   #7
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There is no idle on your generator, constant speed at all loads. What you are likely seeing is waveform distortion from cheap electronic switching type devices. This would smooth out at even slightly heavier loads. This would not be seen on shore power, since it has a VERY large Ďbackupí.

You would have to figure out which device in your electrical system is causing the distortion or extra zero crosses. Could actually even be your Ground Fault AC outlet. A filter could then be used. Alternative generator, maybe a new voltage regulator. Have see this before, it is odd and rare, but understood in tight generator circles.
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Old 09-20-2020, 09:48 AM   #8
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The oscilloscope gave the breakthrough. We measured during load 62Hz but without load a whopping 79 Hz. The inverter read 39Hz so roughly half that. Likely the inverter did not register all peaks at that high frequency. So instead of suspect low RPM the generator now seemed to do too high. I looked into that and indeed saw 2200 instead 1800 at no load. Tuned the Gen set to 1850 at no load and now it works like a charm. Governor needed some finetuning.
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Old 09-20-2020, 11:45 AM   #9
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Old 09-20-2020, 07:07 PM   #10
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Great job, it all works. Sounds like you still have wave form distortion. Would be interesting to see what you get with breakers on gen thrown.

However; if it all works move on to the next item that is broke.
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