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Old 02-04-2019, 03:24   #1
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2 Engines, 1 Starting Battery....Bad?

The boat is a 2011 FP catamaran with two VP D2-40 diesels, sharing one starting battery. There is an emergency cross connect to the house batteries but I've never had to use it.

I had a VP tech aboard yesterday to do some engine work and he noticed the battery configuration and said that it was wrong and that I should have a dedicated starting battery for each engine, otherwise the alternators would be fighting each other.

The boat came from the factory with only one starting battery and I've never had a problem with the battery or starting the engines, so after almost eight years of running, I think the single battery set up is OK, but.....

What's your configuration for your two engines?

Thanks, Pat
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Old 02-04-2019, 05:54   #2
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Re: 2 Engines, 1 Starting Battery....Bad?

Alternators "fighting each other" is not a thing.

Long as it works, and you regularly test your backup option, carry on.
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Old 02-04-2019, 06:17   #3
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Re: 2 Engines, 1 Starting Battery....Bad?

I have mine configured the same way and has never been a problem. As the charge rate tapers off one of the alternators will dominate but that is no problem.
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Old 02-04-2019, 07:24   #4
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Re: 2 Engines, 1 Starting Battery....Bad?

Nice to have a battery for each engine, at least you know you can start one then diagnose the problem on the other one later, all when coming in an inlet or approaching a dock full of mega-yachts!
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Old 02-04-2019, 08:09   #5
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Re: 2 Engines, 1 Starting Battery....Bad?

I usually start mine off of the house bank. I can start either engine off of the house bank or the start battery. I can't see a need for a third battery. My alternators are wired directly to the starter cable so whichever battery is chosen to start will be the one that gets charged.
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Old 02-04-2019, 08:28   #6
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Re: 2 Engines, 1 Starting Battery....Bad?

Alternators fighting each other IS a thing. Or maybe "refusing to fight" is better said and probably what john61 meant. If one kicks in first, the other reads high voltage so doesn't kick in to charge mode. At least with after market alternators and external regulators. That's what occurred on my cat engines if I switched to combine batteries.
One starting battery seems a bit weird to me; very long cables etc but .... it's been working a long time.
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Old 02-04-2019, 09:45   #7
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Re: 2 Engines, 1 Starting Battery....Bad?

I have the same setup. The start battery is charged by the port alternator. The starboard has a oil pressure switch that energize the alternator to charge the house bank. There is a combiner switch to connect both the start and house if needed, Iíve never used it.
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Old 04-04-2019, 02:50   #8
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Re: 2 Engines, 1 Starting Battery....Bad?

Quote:
Originally Posted by pstadt View Post
What's your configuration for your two engines?

Everything on the house battery. No start battery, but an emergency battery that I manually check/charge every month or so. (that is not the standard lagoon setup)



I remember a friend of mine had only one alt charging the house on his FP Lipari. I thought one side started with the "start" batt and the other started on the house batt, but maybe I got that wrong.
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