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Old 14-12-2012, 09:42   #16
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Re: Windlass Wiring and Battery Management

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Originally Posted by Matt sachs View Post
The engines alternator will only supply the cranking battery much like the setup in an automobile, and either a high output alternator or a seperate gen set will be used on the house bank.
If this is crazy, I hope some will let me know....
Fitting two alternators on the main engine and using one for the sart battery and second high capacity alternator for the house battery is OK. A very simple and KISS system. The high output alternator will supply the house batteries needs.

If you only have one alternator on the main engine I would not dedicate this to just to the start battery. The start battery uses very little AHRs and the alternator will be not doing anything most of the time when it could usefully be charging the house bank.

There are lots of ways of diverting the alternator output between the start and house banks. A VSR is the common system. It's a shame to have the alternator doing nothing most of the time.

Have a system in place so that the engine can be started by the house bank. The start battery will fail sooner or later, no matter what you do, sometimes reasonably rapidly.

In summary the main engine needs to able to charge both the start and house batteries. This can be done with two alternators, or splitting the charge of a single alternator as is done successfully in most boats.
To not have the main engine charging the house battery is crazy
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Old 14-12-2012, 09:51   #17
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Re: Windlass Wiring and Battery Management

All this information and logic supports my decision long ago to leave the battery switch on Both and use all my batteries as one big house/start bank. Its simpler, the engines start better, and the batteries last longer.

If you are a liveaboard, you have DAYS to notice that your batteries are getting flat and do something about it. I have had one shorted cell in 20 years, and there was enough juice left in the remaining batteries to roll the main engine, so I didn't even have to wait a few hours for my solar panels/wind gen to recover the bank.

The other urban myth is that you can't combine battery types and ages. You may have to compromise a bit on the charging voltage, but all this nonsense about circular currents is just that--nonsense.
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Old 14-12-2012, 11:21   #18
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Re: Windlass Wiring and Battery Management

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Originally Posted by tartansail View Post
......@sailinglegend -- Interesting point about the starting battery. Doesn't charging via a combiner equate to mixing battery types? My solar setup is going to be floating at 14.3 volts. Wouldn't an AGM be a pretty unhappy camper if the combiner let that through?
My Lifeline AGMs are 14.4 volts and the Red Flash is probably the same, but I can't find online their exact details.

AGMs are not like Gels, some of which should only be charged at 14.1 volts, but check with the battery manufacturer. Not all AGMs are the same.
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Old 14-12-2012, 11:29   #19
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Re: Windlass Wiring and Battery Management

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Originally Posted by sailinglegend View Post
My Lifeline AGMs are 14.4 volts and the Red Flash is probably the same, but I can't find online their exact details.

AGMs are not like Gels, some of which should only be charged at 14.1 volts, but check with the battery manufacturer. Not all AGMs are the same.
Good to know. The height in our battery compartment may be marginal for the start battery. Being able to put it on its side might address the problem if we can't fit a G27 LA upright.
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