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Old 04-10-2013, 12:38 AM   #1
Lt. JG
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Location: Delta, BC, Canada
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Default Battery banks and engine starting query

Any opinions would be appreciated.

I have a 2004, Maxum 3100 with twin 5.0. There is a 2-battery starting bank and a 4-battery house bank. Each bank has itís own charger. The 2 battery switches are labeled port and starboard engines. So the starboard engine is started from the 2-battery starter bank and the port engine is started from the 4-battery house bank. As the engines are out and I now have access to all of the wiring easily I would like to know if it would be better to attach the port engine starter feed together with the starboard engine starter feed from the 2-battery starter bank. That way the house batteries will not have any draw when the port engine is started. Yet the port engine will still charge the house bank and in an emergency I can still switch both switches to both to start both engines. It seems odd to have 2 starting batteries for just 1 engine and using a deep cycle bank to start the other.

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Old 04-10-2013, 12:47 AM   #2
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Typically you have regular starting batts for the engines and deep cycle marine batts for the house. It would be better to isolate the house batts away from the engines.

So, yes, it is odd.

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Old 04-10-2013, 12:59 AM   #3
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Did the PO rewire this? According to the wiring diagram here ( it has 1 battery for STB and 1 battery for PORT engine. It does seem odd to have 2 batteries for one engine and house batteries for the other.
If it were me, I would wire 1 battery to each engine and leave the other 4 as house. Having 2 batteries connected together does nothing at all when 1 dies unless they are isolated with a switch. If they are not, voltage will equalize between the 2 and the dead one will kill the good one. 2 are only needed in large motors that need that extra kick that you just can't get with 1 (and a 5.0 is hardly in that class).
Maybe the PO was trying to 2 have 2 batteries for everything. 2 for STB, 2 for PORT and 2 for House? Maybe a rewire gone bad?
And I do agree 100% with Phillbo, use Marine Cranking batteries for the engines and Deep Cycle for the House.
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Old 04-10-2013, 12:58 PM   #4

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It is very nice be able to start any engine with any battery fro emergency purposes. ideally the engine batteries should be isolated.
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Old 04-10-2013, 01:46 PM   #5
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if it not broken don't fix it......
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Old 04-11-2013, 12:12 PM   #6

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If he 's starting one engine with his house bank and the other with aa dedicated starter, something is not right.

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