How to make a cheap isolated dual-battery setup

Here’s an updated basic diagram, with the fuses for the solar array (buy two panels, then start calling it your solar array, people will think you are either really cool or some diabolical madman bent on world domination)

Using an 80A isolator when trying to automagically jumpstart your car

While you may be able to jumpstart your car by using the smaller current isolator, there is a real chance you will ‘burn up’ the isolator. This happens when the charge between your starting battery and your house battery is great…ie your starting battery is at 8V and house battery is at 12V. When that differential happens, it’s like water flowing down a steep hill instead of a shallow hill – more faster! More current! More cowbell!

Why is this a problem? When isolators ‘fail’ or ‘burn up’ – they don’t always show it! In fact, the most common failure mode for an isolator being exposed to excessive current is to ‘fuse’ the contacts inside, with no evidence showing on the outside! OUCH that sounds bad! What does all that fancy language mean? The isolator will always be on, your batteries will always be connected, and you’ll be draining both at the same time. Fine in town, not so great when you’ve been hanging out in the Nevada desert after the apocalypse and the zombie hordes are coming your way…and your truck won’t start because you’ve drained both batteries drinking mail-order beer out of your cheapo fridge.

Wiring in two separate batteries, with one or two isolators

If you don’t need your two house batteries separate from each other – you want a big battery bank…just wire the two batteries in parallel after the solenoid.

f you want your starting battery isolated from your house batteries and you want your house batteries isolated, you need to isolators. Just hook them both up the same way…sorry I got lazy making pictures, so you’ll need to visualize it

This diagram is really not that complicated. A few things to remember:

I’ve upgraded the ‘jump start’ solenoid to 200A. This gives us plenty of extra capacity to flow current if we want to use the solenoid to jump start our truck instead of using jump cables (lazy bastard). Better yet, order the way good isolator and get 500A!
I also upgraded the fuses to 200A. You know, because if I didn’t do that I might blow a fuse or two (depending on the voltage difference of the batteries, you were paying attention earlier, right?)

I also upgraded my wiring to 2GA. Remember, always overcompensate for the size of your…wire! We could have probably survived with 4GA, but what if we want to put in a winch later? hmmm, 2GA would likely run the winch, 4GA would definitely NOT run a winch. hmmm…500A isolator…2GA wire…winch, 2 fully engaged batteries…this might need it’s very own ‘how to wire up your winch really cheap’ addendum…
I put ‘in dash’ switches for each isolator. This is a little complicated…each switch needs ‘power’ from somewhere in your cab. I’m sure you can find it. Just wire the switches with power from within your cab and then run the wire to the solenoids. By doing this you can ‘turn on’ your solenoids without having to start the truck!
The trailer circuit is 80A. This is likely the most you will ever need. Remember overkill!

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