Second Leisure Battery instal - some help to check my thinking.

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Jun 22, 2022
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Chausson Suite Maxi
I put this question in the Chausson forum, but realised that it probably needs to be in here.

I have a second battery and have identified the space to put it, I just need a little help on wiring.

I have followed the wires out of the existing battery and as far as I can see the first place that they appear is at a split relay box, so I have something that looks like this:

VanWiring1.jpg


'Main' in the picture is the existing LB.

The positive battery cable (25mm) and a much thinner negative cable come from the main leisure battery to the relay.

Can I check my thinking on how I wire in a second LB, please?

I think that I want to end up with it like this:

VanWiring2.jpg


But having looked at the diagram on this page - Second leisure battery

img11.jpg


It looks like I don't have to connect the negatives battery to battery? As long as they are both grounded they will be OK?

It looks like a fuse 'in-line' between the two positives would be a good idea? I have not seen this recommended elsewhere.

Any suggestions gratefully recieved!

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For batteries very close to each other, joined by a wire link, there is very little possibility of the positive coming into contact with a negative or ground, so usually no fuses are used. If they are in separate locations, there's much more possibility of that, for example where the linking wire goes through a hole in a metal panel. In that case two fuses are required, one at each end of the link wire, near each battery. This is in addition to any existing fuse arrangements.

The reason no negative is required is that the current flows through the chassis, which is a solid metal construction that can carry large currents without too much voltage drop. It's a good idea in metal vehicles like a PVC. However in a motorhome with fibreglass/foam/thin aluminium construction it can be hard to find a convenient chassis connection, so a negative link wire might be easier to install, especially since you are installing the positive link anyway.

Make sure the link wires are thick enough to keep the voltage drop below about 3%. The voltage drop depends on the length of wire, and the amps, as well as the cross-sectional area (CSA) of the wire in square millimetres. There are charts and calculators online to give you the voltage drop, such as this one.
 
Last edited:
Thanks, that's very helpful.
 

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