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I'm wiring my caravan into my car this weekend. In order to keep the caravan's leisure battery charged the cars alternator provides a current to the caravan for this purpose.

I need to figure out what gauge wire and fuse I need for this.

Unfortunately my multimeter can only measure up to 10amps DC and I don't want to kill it in the process of measuring the current from the car. I intend to let the leisure battery drop to 12v (about 50% full) at most. I think the voltage from the car is about 14.4v for charging the leisure battery, or around that.

I'm not sure how to calculate a current draw between two voltages.. I suppose a lot of it has to do with the fact these are lead acid batteries?

Some guidance would be very much appreciated. I couldn't find the answer on google.

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  • \$\begingroup\$ Will the leisure battery be 80% drain before you start the next trip again? \$\endgroup\$ – Jason Han Aug 5 '17 at 13:32
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I hope the notes in: http://www.vishay.com/docs/30304/currentmeasurement.pdf and in: http://www.vishay.com/docs/49159/_power-metal-strip-shunts-current-shunts_vmn-pl0005-1409.pdf can help you to measure a low voltage and, indirectly, the big current.

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You need a split charge relay, relevant fuse and good quality wire for 80 amps or so.

This is the type of components that I used for a couple of caravans and the second battery I had on my Landrover that I used for jump-starting other vehicles.

And as for finding info, this link may help :http://www.12voltplanet.co.uk/split-charging.html

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