The Jump Start System

I had a lot of problems when I bought the van with the battery going flat overnight and wanted an emergency jump start system.

When I first bought the van it had a lot of electrical problems and the battery would go flat intermittently from time to time. Although the problem is very rare now since the van has had a new battery and new alternator it does still happen rarely and I thought it might be a good idea to be able to jump start the van from the leisure batteries.

The starter battery of my van has a cranking rating (CCA) of 850 amps. The leisure batteries in my van are Numax LV26MF and have a CCA of 740amps. My batteries are in banks of two under each of the front seats so it struck me that a single bank of two would give me 1480 amps on tap to start the vehicle if needed. I just needed a system in place to join them.

Here is the existing wiring.


What I wanted was to be able to connect the leisure battery bank under the passenger seat to the starter battery. I was advised to use a heavy duty isolator switch (300a) to make the connection by a member on the SBMCC forum and to use at least 25mm cable. What did cross my mind though was the existing cables in the above drawing are fused at 50a and the current used by the starter motor could easily blow these.

I decided to use another isolator to isolate just the passenger seat battery bank. Then to replace the 16mm cable joining these two batteries together with 25mm. I would then run another 25mm cable from this battery bank to the starter battery with the 300a isolator and a higher rated fuse (probably around 300a) added to it.

Here is what I came up with.


Now if I do have a flat starter battery I can switch the isolator between the leisure battery banks off then switch the 300a isolator that connects directly to the starter battery on and start the vehicle. Both of the isolators will be sat together and be accessible by opening the passenger door.

Update – september 2013

When I originally designed the jump start system I was going to use a different battery set-up and charging system. This has now been revised and the way I’m now wiring my batteries (more efficient) means I needed a different jump start solution as well. This is what has now been installed:


It may look complicated but all it really is, is a switch that bypasses the new charger. To make this work all I have to do is turn the isolator switch which lets the current from the leisure batteries flow into and rapidly charge the starter battery. I then leave the van for 10 minutes, turn the switch off again and start the van.

It’s important not to try and start the van with the switch on as this could blow the fuses in the system. It’s just a rapid charging system. But it works 🙂

4 comments on “The Jump Start System

  1. Have you ever had to engage the switch? We have the same CTEK system and have found that it will automatically engage the service battery if the starter is failing… It will momentarily disconnect the consumer circuit…

    • Yes, had to use quite often until recently. Now, finally, the issue is fixed, so the battery doesn’t drain like it always has.

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