How to: Battery Isolator for Van Build

Materials needed for this project →

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Step 1:

Access the car starter batteries and Disconnect the negative wire.

NOTE: My electrical system is made up of two 100ah battle born lithium batteries connected in parallel. I have a 2019 Ford Transit 150. This works for me but may not work for your system if you have a different van or battery bank.

In order to safely handle the car’s starter battery positive terminal (which is where you will be connecting your battery isolator) you need to first remove the negative cable. This breaks the circuit and makes it safe to touch the positive terminal of the battery.

To access the battery terminals, push the seat forward, unbolt a few bolts in the back, remove the metal/fabric covering as well as the plastic bit, unscrew the nut holding the negative wire to the battery’s terminal and set it aside so it won’t accidentally touch the negative terminal.

Push the seat backward to access the front of the starter battery where the positive terminal is. Disconnect this (you will reconnect it with your own positive cable and terminal connector on top of the pre-existing cable soon).

Step 2:

Measure, cut, and fit your positive cable to the starter battery.

Once you have decided where your little isolator will actually go, you can measure the amount of wire you will need to reach the positive terminal on the starter battery.

PRO TIP: I fit a terminal connector onto one side of my 4AWG cable, connected that to the car’s positive terminal of the starter battery, and then fed it through the base of the seat, through my plywood, and into my electrical system before cutting. Rather than measuring, I just held the other end of the wire right where the isolator was mounted and cut knowing that the other end was already connected to the starter battery.

When connecting the terminal connector on the end of your 4AWG cable to the car’s starter battery terminal, make sure you lay the terminal connectors (both yours and the car’s) as flat as possible so that the surface area is maximized.

Step 3:

Mount and connect your battery isolator.

The isolator comes with a small black wire to ground the system. If your electrical system is already grounded you can connect the provided negative wire to your system (I grounded mine to the car chassis via my negative bus bar). Make sure your isolator is close enough to your negative bus bar or the negative posts on your fuse block (this is where I connected mine) to reach given the length of the provided negative wire.

The bottom of the isolator has two posts. One marked for STARTER battery and one for SECONDARY battery. Your car starter battery gets connected to the STARTER battery terminal (after running through the 150a breaker). Then a cable from the SECONDARY terminal runs to the positive bus bar in your system.

Take your 4AWG cable running off the car starter battery, connect it to one of the posts on your 150a breaker, then run another 4AWG cable from the leftover terminal of the 150a breaker to the STARTER battery terminal on the bottom of your isolator.

Take another 4AWG cable and run it from the SECONDARY battery terminal on the bottom of the isolator to the positive bus bar.

Once your negative cable is attached, all the positive cables are mounted and secured properly, and everything is exactly where you want it (screwed down, tightened down etc.) you can reconnect the negative cable in your car’s starter battery.

NOTE: When reconnecting the negative cable you will see a spark. That is normal.

Step 4:

Test your system!

Once everything is reconnected, secured properly, and ready to go you can start up your car and see the isolator kick in! Very exciting.

I used my battery monitor to watch the power flow into my battery bank. The way these work is that when your car’s starter battery is full, all the excess power coming from your car will flow though the isolator and charge your secondary batteries.

An added bonus of this isolator is that your secondary batteries (my battle borns, in this case) will now support the car battery which is amazing. This means I could, hypothetically, start my car using my battle born batteries if my car starter battery was dead. That is super reassuring since I know I will be in some remote places with the van and would hate to wake up to a dead car battery.

Final thoughts:

It is so awesome knowing that my battle born batteries are charging while I am driving. For the simplicity of this install, as compared to building the whole electrical system, I would highly recommend this to someone planning to live full time out of their van (we don’t live in the van we live out of the van).

One thing I would change, if I could go back, I would place another 150a breaker right after the 140a isolator before connecting to the positive bus bar in my system for added peace of mind as far as safety. I know I could go back and do this right now but let’s be honest…it hasn’t exploded yet so the likelihood of going back to fix something not broken is low.

Famous last words?

Originally published on my site,