I have a hybrid car and the 12V battery is under the boot floor, which is awkward to get to if I ever need to jump start the car so I've installed a socket in a more convenient and accessible place and I've taken two wires directly from the battery to that socket.The socket is keyed so there's no chance of any reverse polarity accident occuring if I ever need to use my jump start battery pack but I need to protect that cable run from any sort of accident resulting in a short-circuit, so I bought a 12V circuit breaker rated at 30A (the computers draw less than 20A to get the hybrid system to the 'READY' state).My question is - the circuit breaker has one connection labelled as 'Line' and the other one as 'Load', so is there anything in there that means it will only operate with current flowing in that direction?The wires from the battery to the socket will have a permanent 12V supply on them. If I were to plug anything into that socket then current would flow from battery to socket. However, it's purpose is to do the reverse and provide 12V from an external source to the flat battery so current flow would be from socket to battery, so will the breaker work 'going one way' as an overcurrent device in case of a fault but also allow current flow in the opposite direction when/if needed?Or should I just put a 30A in-line fuse in instead of the breaker?

Google for 'starter motor current'. If a car wont start, I either put it on charge or just go an buy a new battery using a different vehicle.

12V circuit breaker - polarity sensitive?

Feb 07, 2019 Last reply: 7 years ago 24 Replies

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Andy Burns 7 years ago

formatting link

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Bob Minchin 7 years ago

That seems to be more sensible than the original proposal

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Dave Plowman (News) 7 years ago

Assuming the battery had enough left for the ignition, simply jack up one front wheel, put it in top gear, and spin the wheel by hand. Worked a treat.

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Vir Campestris 7 years ago

Back in the early 80s I had a Mini. One winter I found that if the overnight temperature was much below zero it wouldn't start. I found I didn't have to push it very hard to be able to bump start it - single handed - and it really mattered to me to make the battery last another 6 months. I needed the money.

Then we had snow.

Andy

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Dave Plowman (News) 7 years ago

I discovered that with my Mini van too. Until one day it was parked on a steeply camber road, and I couldn't push it away from the kerb between parked cars. Hence the jacking up one wheel trick. The happy days of yoof.

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