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Old 19-05-2015, 16:22   #1
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Check my thinking on backup starting wiring

We had a start battery fail on us. We were in a place where I could easily purchase a new one, but I got to thinking about installing a switch to let me start off the house bank if this happens again and we aren't in a place to buy anything.

The engine is a long way from the house bank and I don't want to run a long length of giant cable just for an emergency start (it is a catamaran and the engine is 25' away from the house bank).

My idea was to put a switch into the 2/0 positive wire running from the alternator to the house bank and connecting a pigtail from that to the starter. Then, if the start battery is bad, I just flip the switch and start off the house.

The connection from the alternator to the house will never be broken doing this - I will either bring an additional wire from the alternator to the switch, or connect the alternator and house together on one of the switch terminals.

The engine was originally wired from the factory to have its alternator output go to the positive terminal on the starter (and then back to the battery), so this seems to be acceptable.

Is there anything wrong with my plan?

Mark
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Old 19-05-2015, 16:26   #2
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Re: Check my thinking on backup starting wiring

I can't see any reason why you shouldn't do that. Just make sure the fuse at the house bank is large enough. Actually you could just jumper from the alternator to the starter in an emergency.
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Old 19-05-2015, 18:07   #3
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Re: Check my thinking on backup starting wiring

Thanks. Jumping the alternator wire to the starter was how I got it working when the battery quit. It is what gave me the idea to put a switch in there because the jumping requires me to get out jumper cables and work over a running engine.

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Old 19-05-2015, 18:39   #4
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Re: Check my thinking on backup starting wiring

I have a twin engine motoryacht. The two engine start batteries are connected via a solenoid which is activated by a momentary switch at the helm. So, if one battery bank is dead, and I have the other engine running, I can "jump" the other battery from the helm.


Why can't things remain where i carelessly left them?
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Old 19-05-2015, 18:43   #5
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Re: Check my thinking on backup starting wiring

Yes, hard wiring in a switch is much safer way of doing it.
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