Specifications: Motorhome - 2003 Fleetwood Expedition 34W - Cummins 5.9 ISB Generator - Onan/Cummins Quiet Diesel 7500Which battery group is best to use to start the generator? Engine batteries? House batteries?Issue #1: House batteries are used for 2000 Watt Inverter. Generator will not start when house batteries are at 10 volt cutoff to the inverter.Issue #2: House batteries are being replaced and I wonder if it would not be best to move the generator start cables to the engine batteries, OR install a separate battery for starting the Onan generator and provide a charging wire from the engine alternator?When the generator is powering the Xantrex Inverter/Charger, the house batteries would be re-charging.

JumboJet wrote:Specifications: Motorhome - 2003 Fleetwood Expedition 34W - Cummins 5.9 ISB Generator - Onan/Cummins Quiet Diesel 7500Which battery group is best to use to start the generator? Engine batteries? House batteries?Issue #1: House batteries are used for 2000 Watt Inverter. Generator will not start when house batteries are at 10 volt cutoff to the inverter.Issue #2: House batteries are being replaced and I wonder if it would not be best to move the generator start cables to the engine batteries, OR install a separate battery for starting the Onan generator and provide a charging wire from the engine alternator?When the generator is powering the Xantrex Inverter/Charger, the house batteries would be re-charging.I believe the house batteries are preferred and if they go dead your battery boost sw. can be used to start the genset. Also starting the main engine should charge the house batteries pretty quickly.

tropical36?Actually, don't you have that reversed? Doesn't the "battery boost" switch you refer to allow the "house batteries" to assist the engine starting battery when it's too weak to start the engine?Maybe I've had the wrong idea all these years.

I got stranded once with dead chassis and coach batteries ... after that I moved everything that was attached to the chassis battery to the coach battery. I also got in the habit of starting the RV before I tried to start the generator - that put all the batteries on-line and generator seemed to start quicker and didn't tax batteries as much.

I have to ask.....why do you want to rewire what Fleetwood designed. You give a lot of reasons why there could be a failure, but none of them will come to fruition if you maintain your batteries, both house and chassis, properly.About the only thing a coach of your era really needs is a battery maintainer that charges your chassis batteries while plugged in. There are three companies that make them, Xantrex, TRIK-L-START and Magnum.

Fleetwood and most others, start the generator off the house batteries. The boost switch works both ways. The house batteries and chassis batteries, should both charge off the shore power (generator), and when the engine is running. Unless you have a COMPLEETE set of 12 volt wiring plans, I would be very shy of re-wiring a MH, as you could miss something important, that could cause a fire down the line.

Onan Generator Starter Battery - Which one? | Good Sam Community

14 Replies

tropical36
Explorer
Aug 06, 2015
JumboJet wrote:
wildmanbaker wrote:
Not the wiring plans that Fleetwood will send you, but the build/repair plans that are used to build the MH, and RV techs use for repair. Before just replacing the batteries, use a hygrometer to test the cells. Use a manual charger overnight, and test again after an hour of rest. If the hygrometer and a voltage test are good, a load test can be performed. If the batteries are good or replaced, you really need to find out what the hidden loads are, to prevent draining the batteries.

Batteries are swollen and leaking acid out the top. The engine starting batteries are relatively new. The previous owner (has had coach since 2006) does not know the age of the Trojan T-105 6 volt batteries. I do know they will not hold a charge and will not start the generator unless the coach engine is running. The previous owner kept a trickle charger on the batteries.

I figure when you turn the switch off to the batteries, they should maintain a nominal charge enough to crank the generator within 24 hours. They are not doing that.

Changed out my Sam's house batteries last week after six years. First found them dry and filled with water, then they boiled and were so hot, I couldn't touch them. My battery sw. only turns off power to the house and not from the converter charger itself. I'd hate to see a battery explode and hopefully that doesn't happen. Either way, I certainly didn't like this scenario.
GrampaR123
Explorer
Aug 06, 2015
Is no one paying attention to JumboJet's posts? He keeps telling you how and why his batteries are toast and all he keeps getting are suggestions on how to resurrect them. His original post question seems to have been lost in the shuffle, somehow.
cj7365
Explorer
Aug 06, 2015
JumboJet wrote:
Specifications:

Motorhome - 2003 Fleetwood Expedition 34W - Cummins 5.9 ISB

Generator - Onan/Cummins Quiet Diesel 7500

Which battery group is best to use to start the generator? Engine batteries? House batteries?

Issue #1: House batteries are used for 2000 Watt Inverter. Generator will not start when house batteries are at 10 volt cutoff to the inverter.

Issue #1: House batteries are used for 2000 Watt Inverter. Generator will not start when house batteries are at 10 volt cutoff to the inverter.

Issue #2: House batteries are being replaced and I wonder if it would not be best to move the generator start cables to the engine batteries, OR install a separate battery for starting the Onan generator and provide a charging wire from the engine alternator?

When the generator is powering the Xantrex Inverter/Charger, the house batteries would be re-charging.

I would be concerned about letting my batteries drop down to 10volts, this is a killer on your batteries

An easy fix, is start your gen set, before your batteries get down that low
JumboJet
Explorer
Aug 06, 2015
wildmanbaker wrote:
Not the wiring plans that Fleetwood will send you, but the build/repair plans that are used to build the MH, and RV techs use for repair. Before just replacing the batteries, use a hygrometer to test the cells. Use a manual charger overnight, and test again after an hour of rest. If the hygrometer and a voltage test are good, a load test can be performed. If the batteries are good or replaced, you really need to find out what the hidden loads are, to prevent draining the batteries.

Batteries are swollen and leaking acid out the top. The engine starting batteries are relatively new. The previous owner (has had coach since 2006) does not know the age of the Trojan T-105 6 volt batteries. I do know they will not hold a charge and will not start the generator unless the coach engine is running. The previous owner kept a trickle charger on the batteries.

I figure when you turn the switch off to the batteries, they should maintain a nominal charge enough to crank the generator within 24 hours. They are not doing that.
jwmII
Explorer
Aug 06, 2015
wildmanbaker wrote:
Not the wiring plans that Fleetwood will send you, but the build/repair plans that are used to build the MH, and RV techs use for repair. Before just replacing the batteries, use a hygrometer to test the cells. Use a manual charger overnight, and test again after an hour of rest. If the hygrometer and a voltage test are good, a load test can be performed. If the batteries are good or replaced, you really need to find out what the hidden loads are, to prevent draining the batteries.

HyGrometer? Not really. A hydrometer would work better, Really.
jwmII
Explorer
Aug 06, 2015
ksg5000 wrote:
I got stranded once with dead chassis and coach batteries ... after that I moved everything that was attached to the chassis battery to the coach battery. I also got in the habit of starting the RV before I tried to start the generator - that put all the batteries on-line and generator seemed to start quicker and didn't tax batteries as much.

Electricity flows both ways.
wildmanbaker
Explorer
Aug 06, 2015
Not the wiring plans that Fleetwood will send you, but the build/repair plans that are used to build the MH, and RV techs use for repair. Before just replacing the batteries, use a hygrometer to test the cells. Use a manual charger overnight, and test again after an hour of rest. If the hygrometer and a voltage test are good, a load test can be performed. If the batteries are good or replaced, you really need to find out what the hidden loads are, to prevent draining the batteries.
JumboJet
Explorer
Aug 05, 2015
wildmanbaker wrote:
Unless you have a COMPLEETE set of 12 volt wiring plans, I would be very shy of re-wiring a MH, as you could miss something important, that could cause a fire down the line.

I do have a complete set of wiring plans - AC and DC.

Like another person said -
ksg5000 wrote:
I got stranded once with dead chassis and coach batteries

The Xantrex charger is toast and being replaced. The house batteries were showing only 9.71 volts. The engine batteries did not have enough voltage to crank the diesel engine.

I am replacing the 6 volt batteries (I have no idea how old they are and individually, each showed less than 5 volts) and replacing the Xantrex Inverter/Charger.

The battery boost emergency switch does NO good when you do not have enough voltage to start the engine or the generator.

There must be enough load on the batteries to drain marginal batteries in just a few days. The engine was cranked on Thursday and operated for about an hour and the batteries were down on Monday.
DrewE
Explorer II
Aug 05, 2015
GrampaR123 wrote:
tropical36?
Actually, don't you have that reversed? Doesn't the "battery boost" switch you refer to allow the "house batteries" to assist the engine starting battery when it's too weak to start the engine?
Maybe I've had the wrong idea all these years.

The battery boost/emergency start switch usually just connects the two together, much like you could do manually with jumper cables. Usually it's intended to allow one to start the main engine when the chassis battery is run down, but the wiring and solenoid controlled by the switch don't care which direction the electrons flow.
wildmanbaker
Explorer
Aug 05, 2015
Fleetwood and most others, start the generator off the house batteries. The boost switch works both ways. The house batteries and chassis batteries, should both charge off the shore power (generator), and when the engine is running. Unless you have a COMPLEETE set of 12 volt wiring plans, I would be very shy of re-wiring a MH, as you could miss something important, that could cause a fire down the line.