Connecting Batteries Together. (1 Viewer)

indytravels

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Dec 28, 2018
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I am fitting 3x 100w solar panels and connecting them to the batteries via a Votronic MTTP 350 Dual controller.

The two leisure batteries seem to be connected together (in parallel) at the built in battery charger, would I be better to also connect the two batteries (in parallel) with direct cables?
The cables going into the charger look quite thin, when I connect a separate battery charger to one battery and take a reading from the other it reads 0.10v lower than the one with the charger connected.

My plan is to connect solar to one battery and a b2b charger to the other battery. Any advise greatly appreciated.
 
Mar 23, 2012
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sleights
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Not an expert but I would have thought the max charging current to be a lot lower than the max output from the battery if say an inverter was being used so should be fine. Of course it could be said the thicker the better to avoid any loss
 

Lenny HB

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Oct 18, 2007
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Since 2008 & many years tugging
The batteries should connected together next to each other not at the charger. Use a decent size cable at least 16 mm sq. While at it worth replacing the cables to the charger as well. If it's a Brit van they are famous for using well under size cables.
 
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indytravels

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Dec 28, 2018
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About to buy one
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Caravan since 1985
Thank you everyone for your help and advise. I will be connecting the two batteries together using 16mm cables, and connect the solar panels/b2b across the two batteries.

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Apr 27, 2016
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The cables going into the charger look quite thin, when I connect a separate battery charger to one battery and take a reading from the other it reads 0.10v lower than the one with the charger connected.

My plan is to connect solar to one battery and a b2b charger to the other battery. Any advise greatly appreciated.
When connecting batteries in parallel banks, it's best to use thick wire to minimise voltage losses. But more important is to arrange the connections so the voltage losses are equal. Otherwise one battery will always be charged slightly less than the others, which is detrimental long-term.

If there's just one charger source, then having equal lengths all the way from battery to charger is one way of doing this. It doesn't work so well with multiple charging sources.

The arrangement in @tacr2man's post is a popular alternative for two batteries. For more than one charge source (B2B, Solar) connect them all to the same terminals as the charger, not to different ones.
 

Abacist

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Oct 15, 2013
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My plan is to connect solar to one battery and a b2b charger to the other battery. Any advise greatly appreciated.

Personally I would connect the two batteries together with large cables to form one big battery and then connect the solar controller to the batteries and also the B2B charger. Then you will have the B2B charging as you are driving along and the solar charging when you are parked up. You then have the best of both worlds as both batteries are being charged simultaneously making more power available at any one time.
 

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