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Old 07-20-2021, 05:15 PM   #1
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Default Start RV from House Battery

Anyone know if you can jumper the House batteries to a dead chassis battery to start the engine ?

One-year-old house battery has Twice come up dead out of 50 times. Can't seem to find out what can draw down the battery with the key off and transfer switch off. Any ideas are welcome.
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Old 07-20-2021, 05:54 PM   #2
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Anyone know if you can jumper the House batteries to a dead chassis battery to start the engine ?

One-year-old house battery has Twice come up dead out of 50 times. Can't seem to find out what can draw down the battery with the key off and transfer switch off. Any ideas are welcome.

We can do it our 07 Raodtrek, but when I upgraded the electrical I made sure I used large enough components to do it safely.


You would need to get rid of the automatic battery separator that ties the front and rear together or jumper around it when needed, most likely need to upsize the cable to the rear along with the circuit breakers in that cable.


If you don't have the lithium or an engine generator you would probably have a #4 cable and 80 amp breakers in to the coach which isn't large enough for engine starting. We have very large cabling and battery capacity so no problem there, and use a manual charge relay to combine the front are rear batteries so very easy for use to do with a switch.



Don't just jumper around the existing separator without confirming the wiring can handle it. It is OK to charge the chassis battery from the coach on shore or solar power though, and the separator should do that for you automatically.
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Old 07-20-2021, 07:02 PM   #3
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We can do it our 07 Raodtrek, but when I upgraded the electrical I made sure I used large enough components to do it safely.


You would need to get rid of the automatic battery separator that ties the front and rear together or jumper around it when needed, most likely need to upsize the cable to the rear along with the circuit breakers in that cable.


If you don't have the lithium or an engine generator you would probably have a #4 cable and 80 amp breakers in to the coach which isn't large enough for engine starting. We have very large cabling and battery capacity so no problem there, and use a manual charge relay to combine the front are rear batteries so very easy for use to do with a switch.



Don't just jumper around the existing separator without confirming the wiring can handle it. It is OK to charge the chassis battery from the coach on shore or solar power though, and the separator should do that for you automatically.

Thanks Booster. In an emergency can you just use a single jumper cable to jump around the isolator?
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Old 07-20-2021, 07:20 PM   #4
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Thanks Booster. In an emergency can you just use a single jumper cable to jump around the isolator?

Yes, but only if your wire size to the coach and breakers in that cable are big enough to carry starting level currents which are often over 100+ amps. If your setup was like ours, you would be limited to 80 amps and may or may turn the motor, but probably would overheat connections, and would trip the 80 amp breakers.
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Old 07-20-2021, 09:21 PM   #5
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I can't tell you how many times I've come up with a dead battery in my RV. I could call AAA, but instead carry a Clore Automotive Jump-N-Carry 12 Volt Jump Starter. It can stay plugged in all the time, so whenever we're on shore power it can recharge. Easily starts the diesel in my Roadtrek Sprinter. Check with Amazon.
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Old 07-20-2021, 11:40 PM   #6
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Some MH have a monetary switch that connects house batteries to motor battery. You hold it down for several minuets and then start motor.
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Old 07-21-2021, 12:39 PM   #7
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Thanks Booster. In an emergency can you just use a single jumper cable to jump around the isolator?
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Yes, but only if your wire size to the coach and breakers in that cable are big enough to carry starting level currents which are often over 100+ amps.
True. Or, you can jump it and wait for the weak battery to draw from the full house battery. It would be best if one has a genset to run, charging the house and vehicle batteries, so you don't end up with dead house batteries too. Disconnect the jumper before trying to start.

I'm going to check my set up, because I think that I might be able to jump the directly from my house batteries with 12' jumper cables.
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Old 07-21-2021, 01:03 PM   #8
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True. Or, you can jump it and wait for the weak battery to draw from the full house battery. It would be best if one has a genset to run, charging the house and vehicle batteries, so you don't end up with dead house batteries too. Disconnect the jumper before trying to start.

I'm going to check my set up, because I think that I might be able to jump the directly from my house batteries with 12' jumper cables.

Yes, you can try that, but often there is either a high inrush of current that will trip small breakers if the battery bank is big enough. In other cases there may not be enough voltage difference to get the staring battery high enough charge to start. Biggest risk is that you can wind up with all the batteries dead, but you might also start the engine.


If you use the 12' cables, you usually can use both cables on the positive side of the connections and none on the negative as the grounds are already tied together in the van. This will give less voltage drop in the cables which tend to not be very big wire so lots of voltage loss.
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Old 07-22-2021, 05:36 AM   #9
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This isn't the same thing; I carry a small lithium jump starter with me. I used it for my RV once, I had an appointment to get a new house battery installed and it turned out the vehicle battery was dead.

I have used it numerous times to start other vehicles and friends' vehicles. One friend liked it so much he purchased one.
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Old 07-22-2021, 06:49 PM   #10
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This isn't the same thing; I carry a small lithium jump starter with me. I used it for my RV once, I had an appointment to get a new house battery installed and it turned out the vehicle battery was dead.

I have used it numerous times to start other vehicles and friends' vehicles. One friend liked it so much he purchased one.
I carry the same with me. It's a small package. Smaller than carrying a coil of jumper cables. That said, I've never used it. I've had friends who have used theirs on vans (not RVs) and they've said it worked well.
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