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Old 04-02-2013, 08:25 AM   #1
4 Rivet Member
raveson's Avatar
1989 34.5' Airstream 345
boca raton , Florida
Join Date: Aug 2006
Posts: 284
Generator info

Had an ONAN dealer service my 6500 Emerald III gen yesterday. One of the problems is the gen will not charge the chassie batttery when running. Long story short, machanic first said the wireing was all backwards. The gen should run off the coach batteries. When checking further, he found that the Emerald III was capable of charging the chassie battery, but some part of the windings had failed. Easiest soliution(suggested by him) is to get a 3-5 amp trickle charger and charge through the univolt system. Also if you have service, make sure that the commutaters and brushes are checked and serviced. Found out that this had not been done since the gen was new (1989) much to my surprise. 3 years ago, that cost me a burned out voltage regulator which cost in the range of $450. Brushes were hanging up that results in arching that leads to the comutater needing to be honed/polished. Worst thing, when they replaced the regulator the brushes were not checked. This can be determined by looking at the screws that hold the brushes in place. If they still have the orig silicone goop over the heads have someone open up and service them.
Happy motoring!

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Old 04-02-2013, 07:42 PM   #2
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1974 20' Argosy 20
Richmond , Kentucky
Join Date: Jan 2003
Posts: 5,139

I just went through this recently with my Onan Emerald III out of the 86 345. In most cases the problem is actually a diode on the control board that goes bad. That's what happened to mine. I haven't taken the time to get a control board as yet but will when it comes time to install the generator in the motorhome.

Onan Emerald III control board

If you use the coach batteries for starting the generator then anytime the generator is running the coach DC converter should be charging the coach batteries. So in reality having the charging circuit functional isn't really that big of an issue.


Air forums # 1674
1974 20' Argosy Motor Home
1974 31' Excella trailer (parting out, as of 4/1/2015 I have wheels, brake drums, windows & holding tanks left to sell)
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Old 04-03-2013, 07:45 AM   #3
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1989 34.5' Airstream 345
boca raton , Florida
Join Date: Aug 2006
Posts: 284
Looking at the bill, I believe it is a diode. Replaced that board 3 years ago, think the trickle charger will be a better fix. As long as I'm plugged to shore power or on gen, both battery areas wil be trickle charged.
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