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Old 02-07-2017, 09:19 AM   #1
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Diesel Onan Generator stays at medium idle

I have a Onan HDKAJ1145D generator in my '98 Monaco Dynasty. After start up it goes into high idle then to medium idle but will not drop to low idle. Nothing in the coach is on. I can turn the microwave on and it jumps to high idle and then back to medium when the microwave goes off. Any thoughts would be appreciated. Thanks
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Old 02-07-2017, 09:23 AM   #2
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Is this a new occorance ?

If it's a new problem, try switching off the generator breakers, to make sure something isn't drawing power.
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Old 02-07-2017, 09:39 AM   #3
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When I cut the breaker to the A/C units, it dropped to low idle. But the A/C units were not on and the A/C thermostat was off too. One other odd note is that there is a foul smell in the RV. Similar to a rotten egg.
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Old 02-07-2017, 09:50 AM   #4
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Now it's time to check your batteries.they may be dry and causing your charger to overwork.
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Old 02-07-2017, 10:02 AM   #5
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OK--new info here--seems you no longer have a generator issue. Assume you have at least two A/C units, so at least two a/c breakers--which one causes the idle up? Eventually, you need to methodically shut off all 120v breakers, then turn on and off one at a time until you isolate which circuit is drawing power and causing genset to idle up--to include you main inverter circuit. More important--the new info on rotten eggs smell suggest battery gassing, or a potential electrical issue--wouldn't leave genset or shore power on until you find the source. Once you have the source isolated, we can begin to diagnose the root causes.
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Old 02-07-2017, 10:05 AM   #6
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Yep, One house battery has acid boiling out of caps. That's the smell.
How do I know if it's just a bad battery or some other electrical problem that caused the battery to go bad? Thanks for all the help.
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Old 02-07-2017, 10:20 AM   #7
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FYI - I have two house batteries (Interstate SRM-4D) Only one has gas coming out of it.
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Old 02-07-2017, 10:26 AM   #8
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Modest amount of acid from top of an older bat is not unusual--turn off the charger function on your inverter for now and refocus on isolating the mystery draw on your 120v side. Concern here is that if you have everything turned off, yet you have a draw, its also happening on shore power.
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Old 02-07-2017, 10:52 AM   #9
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Something to be aware of, the generator prime mover RPM is what set's the AC frequency at 60 Hz. When the engine is first started the RPM will normally vary a bit until the governor takes over and locks the RPM to maintain the 60 Hz and 120 Volts. In most, but not all generators, that would be 3600 RPM. As you add loads there can be a momentary RPM change as the governor-engine-generator react but it will settle with in a seconds or two back at 3600. The higher loading will cause the tone or pitch of the engine to change which can be mistaken as an RPM change. Based on the initial question I would say your generator is working as expected. The one variable is if a generator is the inverter type which the Onan is not.

Concerning your batteries based on your statement, "One house battery", I'm guessing you have two or more. If the other batteries are OK then your convertor/charger and various house loads are OK. Batteries go bad sometimes with nothing external causing the failure. Also the one failed battery could be shorted internally and if so it will consume the other batteries in the bank. As such you might have to replace all of them.
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Old 02-07-2017, 11:10 AM   #10
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SB--think you missed the OP's point--changes in genset idle speed seemed to be related to turning a breaker on and off. Example was A/C breaker with unit off? Concerned OP has a significant 120v issue that needs to be addressed first, then sort out the battery issue.
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Old 02-07-2017, 11:31 AM   #11
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Quote:
Originally Posted by Sweetbriar View Post
Something to be aware of, the generator prime mover RPM is what set's the AC frequency at 60 Hz. When the engine is first started the RPM will normally vary a bit until the governor takes over and locks the RPM to maintain the 60 Hz and 120 Volts. In most, but not all generators, that would be 3600 RPM. As you add loads there can be a momentary RPM change as the governor-engine-generator react but it will settle with in a seconds or two back at 3600. The higher loading will cause the tone or pitch of the engine to change which can be mistaken as an RPM change. Based on the initial question I would say your generator is working as expected. The one variable is if a generator is the inverter type which the Onan is not.

Concerning your batteries based on your statement, "One house battery", I'm guessing you have two or more. If the other batteries are OK then your convertor/charger and various house loads are OK. Batteries go bad sometimes with nothing external causing the failure. Also the one failed battery could be shorted internally and if so it will consume the other batteries in the bank. As such you might have to replace all of them.
I'm taking the leap that the OP has a diesel powered, inverter generator. Maybe 1800 RPMs at full load. It runs near 1000 RPm and as the loads increase, so does the RPM.

If one of the batteries is shorted, it will call for a lot of amps. That will make the charger draw more AC amps.

Of course that also happens when plugged in to shore power but not noticeable, like the generator.
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Old 02-07-2017, 11:34 AM   #12
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Originally Posted by 411jeff View Post
Yep, One house battery has acid boiling out of caps. That's the smell.
How do I know if it's just a bad battery or some other electrical problem that caused the battery to go bad? Thanks for all the help.
If they are tied in parallel, + to + and - to -, and one is boiling, that one is bad. Not that it matters because if they are the same age, you should change both now.
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Old 02-07-2017, 11:52 AM   #13
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So the breaker I turned off that allowed the generator to idle down looks to be the one that feeds AC current to the RV. I was thinking it was just the A/C (air conditioner) breaker.
So now I assume AC power (Generator or shore power) goes through this breaker and then feeds the inverter/charger. Would that be correct?

As Twinboat stated: If one of the batteries is shorted, it will call for a lot of amps. That will make the charger draw more AC amps.

Now does this make sense that the generator was idled up due to the battery short and the inverter/charger needed more power?

If that is a YES then I'm down to why the battery overheated.
Faulty battery or an inverter/charger issue? Since I have two house batteries and only one looks to be overheated, I guess it was just the battery?
I've never had a battery just over heat. The water level as of one week ago when I checked it was fine. And only 2 chambers are low on water now after being overheated.

Once again, thanks for everyone's advice.
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Old 02-07-2017, 12:34 PM   #14
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I've had a set of three 4D batteries overheat, one at a time as I removed the offending one. It was a few months after I bought the boat.

I replaced them with 6 volt GCs, using the exact same charger, and didn't have any problems.

The cells just short out when they shead their lead.
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