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Old 31-03-2010, 08:35   #1
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Help Needed! - Wiring Alternator to Charge House Batteries

New engine comes fully wired, and the alternator is prewired to charge the battery that connects to the starter motor. Of course, that battery is my dedicated engine starting battery, which I use for nothing more than starting the engine. The old engine which I just replaced had an alternator with a large ground stud as well as the positive connection, so I connected the alternator to a diode onto which I then connected the house batteries and the engine starting batteries. It was a lot of wiring. I am wondering whether I can charge the house banks by simply connecting them to the engine starting battery using the 'both' switch on my battery selector switch?? Can anyone help?

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Old 31-03-2010, 08:54   #2
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Yes, it takes some remembering, but you could switch to BOTH while motoring. Then back before shutting down....depending...will help if all batteries are the same general type...flooded...AGM...etc. You can buy a little relay box from West MArine that does this automatically. Diodes are problematic.

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Old 31-03-2010, 10:20   #3
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Originally Posted by daddle View Post
Yes, it takes some remembering, but you could switch to BOTH while motoring. Then back before shutting down
I would switch AFTER shutting down the engine. We have the standard Guest make-before-break two bank switch/breaker. Despite its design, switching from 1 to both or both to 2 etc. will cause instruments to beep as they reset. I assume the problem is due to corrosion or oxidation on the switch contacts. Given the danger of blowing the alternator by having it disconnected momentarily from the battery load I never switch battery settings with the engine running.

Overcautious ? Maybe.

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Old 31-03-2010, 10:42   #4
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See the Blue Sea Systems Application Briefs on Battery Switching
Resources - Blue Sea Systems
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Old 31-03-2010, 10:45   #5
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Maybe we could be of more assistance if we knew more about your boat and the specific setup, e.g.,

1. type and size of boat;
2. size of house bank and type of batteries;
3. type and size of alternator and whether internal or external regulator;
4. type and size of battery charger; and
5. type of service intended (weekend sailing, long-term cruising, etc.).

All these factors are relevant to decisions about charging systems.

The preferred configuration these days is for an alternator with an external regulator with the alternator output connected directly to the house battery bank (only), with an appropriate fuse or breaker in-line near the battery bank. The starter battery could be efficiently and automatically handled with an EchoCharge device, which bleeds off a bit of the current from the house batteries as needed whenever it senses a charging voltage on them. This arrangement is completely automatic and avoids all manual battery switching --less chance to make potentially serious and costly mistakes.

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Old 31-03-2010, 11:09   #6
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Sounds like the problem I faced when switching from the 3GM30 to the 3YM30.
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Old 04-04-2010, 15:09   #7
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btrayfors nailed it in Post #5: +1


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