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Old 06-13-2018, 08:14 PM   #1
Junior Member
Brand: Still Looking
State: California
Posts: 16
THOR #11959
Using emergency start to charge coach battery with engine

I have a 2003 Isata that doesn't charge the coach batteries while driving. That's just fine 98% of the time since the coach battery get charged from shore power. Occasionally, we won't have shore power for a two or more days in a row.

The RV has and emergency battery switch and solenoid that connects the coach and chassis batteries in parallel in the event the chassis battery is too low to start the engine. I noticed when the switch is down and the engine running the coach battery's voltage goes up to 13.05v indicating it's charging, The engine voltage regulator charges the chassis battery at 14.3. Since the wiring that connects the 2 batteries in parallel is pretty robust, I don't know where over a volt is lost.

The question is.... Occasionally, can I drive with the emergency parallel switch on to charge the coach batteries? I understand if the coach batteries are fully depleted a rather high current could result and won't let that situation happen. Any other issues or dangers I'm not seeing?

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Old 06-13-2018, 08:51 PM   #2
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Brand: Still Looking
Model: 2019 Coachman Catalina
State: Wisconsin
Posts: 216
THOR #5432
The batteries of the coach should be charging when you are driving down the road. If the switch is down then the emergency start is probably off and that is why it is charging. That would be my thought anyway.

2019 Catalina
Towed by 2019 F250
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Old 06-13-2018, 09:37 PM   #3
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Brand: Thor Motor Coach
Model: ACE 27.1
State: Florida
Posts: 5,361
THOR #7035
The same solenoid that cross-connects the 2 battery systems for emergency start also cross-connects them for charging. Most emergency start switchs are momentary, hold to on, spring return to off.

The real question is why isn't that solenoid closing as exprected to cross-connect while charging? The low supply voltage from the engine side may have something to do with it.

I've never seen a bad or loose connection on a Thor product though ........
Ted & Melinda
2016 ACE 27.1
2016 Chevy Sonic Toad
2020 Chevy Colorado Z71 Trail Runner Alternate Toad
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Old 06-13-2018, 11:18 PM   #4
Junior Member
Brand: Still Looking
State: California
Posts: 16
THOR #11959
I've read some RVs charge the coach batteries while driving, others don't.

This one does not charge the coach batteries. There is only one solenoid in the battery control box and most wiring diagrams I've found have 2. I don't know if it design that way or something is defective.

My emergency switch is also momentary, but easy enough to latch down.

So, you all think, the two batteries should be connected in parallel when the engine is running, separated when the engine is off (except for emergency starts)?
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