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50ft narrowboat twin alternaters one for leisure batteries one for engine battery can i connect negitives to all batteries at present two seperate systems

Asked by: bruce  | 9.47pm, Sunday 3 April

WW says:

I am assuming that the battery isolators are in the positive line. The negatives can certainly be connected together, but I think you will find that they already are (unless the alternators are isolated)! This is because the alternators are bolted to the engine and the negative connection is usually to the body of the alternator.
If it is all working fine, I would leave it alone as connecting the two sets together will create a earth ring which could cause problems. If all is not working properly then try and identify the earth connections for the two battery banks. You will definitely have a thick cable from the starter negative to the engine for the starter motor, this usually forms the single earthing point for the electrics. If you have another from the cabin battery negative to the engine or alternator, all should be fine.
Generally there should only be ONE earth connection to the engine and hence the hull. An earth loop can generate circulating currents which can erode the steel hull if it is part of the circuit!

Rupert Smedley  | 9.57AM, Wednesday 6 April

Readers say:

Thanks for answer, all is working ok so will leave well alone.

bruce  | 12.09PM, Thursday 7 April

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