Howdy, I am thinking about changing my emergency start swtich from the stock momentary type to a single pole, single throw, switch with a hinged cover. Want to have the option to draw from the engine battery if needed, if I kill the coach battery bank. What do you all think about this? Thank you

i think you will instantly regret it the second you drag your engine battery down enough to not be able to start the engine. there is a reason its momentary

On my rig the momentary switch energizes a relay that ties the two battery systems together temporarily.After my chassis engine starts the same relay is energized to charge the house batteries.The idea of the momentary operation, is to allow the electronics to take over.Putting a non-momentary switch in could cause other issues in the battery control center.I would not do it as we do a lot of dry camping away from any help.

The POWER on the emergency start switch comes from the Coach Batteries. If you use a SPST, that will have the solenoid energized all the time. IF you are drawing battery power, that means you will draw BOTH battery banks down dead together and you will NOT have any battery power to jump. Doug

Doug is right that is a fairly hefty relay, it has considerable power drain that you don't wantWhen the engine is not runningYou really don't want to be using the engine battery to support the house batteriesIf you don't have enough house battery, then that is the situation that needs to be addressed

I think it's a bad idea, especially because of your intended use. You could pretty easily find yourself with no battery power to do anything, be it start the main engine or start the generator. The starting battery is not a deep cycle battery and isn't particularly well suited for significant discharges; it's instead more optimized to supply brief, high currents such as the starter needs.On many motorhomes, the same relay is used for the emergency start as for the battery isolator system, as was mentioned, and often this is controlled for the isolator system by the engine run power line from the key switch. If that's the case, you can combine them temporarily by putting the key in the run position without starting the engine. I sometimes do this when exercising the generator for the opposite reason--to try to keep up the starting battery charge during longer-term storage.

Emergency Start Button - Connects both Battery banks

23 Replies

dougrainer
Nomad
Apr 19, 2017
The POWER on the emergency start switch comes from the Coach Batteries. If you use a SPST, that will have the solenoid energized all the time. IF you are drawing battery power, that means you will draw BOTH battery banks down dead together and you will NOT have any battery power to jump. Doug
enblethen
Nomad
Apr 19, 2017
On my rig the momentary switch energizes a relay that ties the two battery systems together temporarily.
After my chassis engine starts the same relay is energized to charge the house batteries.
The idea of the momentary operation, is to allow the electronics to take over.
Putting a non-momentary switch in could cause other issues in the battery control center.
I would not do it as we do a lot of dry camping away from any help.
LittleBill
Explorer
Apr 18, 2017
i think you will instantly regret it the second you drag your engine battery down enough to not be able to start the engine. there is a reason its momentary

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Emergency Start Button - Connects both Battery banks

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