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Old 03-09-2010, 02:45 PM   #1
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Starting Engine with House Battery on SMB with Isolator

Hi guys,

I am running a 2003 E-350. 12V electrical system only, no inverter. Isolator, not separator. Lifelife 4D battery.

My understanding is that with an isolator, it is not possible (given the factory setup) to start the engine with the House battery. SO - if I'm out in the middle of nowhere and my Starter battery dies, it would be no help to me that my House battery is still pumping 12.5V. First off, do have this right? Secondly, what have other folks with my setup done to get around this? Right now I'm thinking a set of 20-foot long jumper cables (and removal of the cabin floor to get to the House battery) would be the best way to get the job done. Any cleaner/smarter solutions out there that don't involve installing a separator or hauling around 30 lbs worth of jumper cables?

Sorry if this is a repeat thread, but I searched and couldn't find the info I needed.



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Old 03-09-2010, 04:47 PM   #2
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Re: Starting Engine with House Battery on SMB with Isolator

I'm thinking the long jumper cables is your best answer.

And you should always carry them so you can jumpstart my van!

Take a look at a 6.0 van. On the side of the frame there are places to connect jumper cables. It might make sense to do something like that so the jumper cables could be shorter.


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Old 03-09-2010, 07:14 PM   #3
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Re: Starting Engine with House Battery on SMB with Isolator

You also might be able to add and heavy duty relay (such as a seprator) and have a circuit wired between the batteries. Another solution would be to put in a correct size inverter that could run a battery charger...provided the starting battery will hold a charge it might take an hour to bring the battery back up but better than nothing. I agree with Mike on the jumper cables but the house battery would have to be full enough to help in any of those situations. A diesel engine could be hard to start no matter what and a generator running a charger might be needed if the house battery is low. Gas engine is more forgiving. Just don't totally depend on jumper cables always.
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Old 03-09-2010, 08:25 PM   #4
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Re: Starting Engine with House Battery on SMB with Isolator

If your isolator is more accessible you should just be able to move the battery cables to one stud together, thus tying the house to the starter through approved cable sizes.

Alternatively invest in a BlueSea separator with an override switch.
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Old 03-09-2010, 09:23 PM   #5
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Re: Starting Engine with House Battery on SMB with Isolator

If you were to choose to replace the isolator with a separator you will need to look at changing the wiring also. Also the existing wire from the isolator will probably not enough for the current transfer needed in starting 4Ga under 10ft and 2Ga over 10ft. If you really want to keep the isolator you can try wiring a battery switch so that you go from battery to battery in parallel to the existing isolator. When you need it you turn the switch, this could be a manual switch or if you could go with a solenoid type switch. In the end you might be better off to purchase a separator either the new Blue Sea or SurePower. I just ran a switch in parallel to my separator you can take a look at this thread viewtopic.php?f=13&t=4353. It should give you some ideas, I apologize for the hard read, but I have always been more proficient at the technical side of things versus the writing side.

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