Please, a definitive word on battery stategy - SailNet Community

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  #1  
Old 07-18-2007
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Please, a definitive word on battery stategy

OK, I'm a daysailor with cruising pretensions, by which I mean I have a 1976 Newport 28 with an inboard Atomic 4 gas engine, with a 24 series starting and deep cycle marine battery for the house, but yet never sail more than a few hours at a time. Right now I have a battery switch that is "make before break", but I do not think it is has the protection for the alternator if the switch is set to "off" while the engine is running. What I'm looking for is the most efficient charging strategy for my batteries. I've read beaucoup articles on this subject but can't figure out the best system for me.

Should I:

(1) run the blower off the starting battery , start the engine off that battery, then switch to "both" while the engine is running to recharge the starting and house batteries. Then run all accessories off the "house" battery while sailing, and switch to the starting battery to restart the engine and reset to "both'" to recharge while motoring back to the dock?

OR

(2) set the switch on "both" to run the blower and start the engine, leave it there while motoring out, use the "house" battery while under sail only, then switch back to "both" to restart the engine and leave it there while motoring back in?

Under scenario 2 I fail to see the need for a starting battery at all, but only a big bank of deep cycle "house" batteries. I must be looking at this wrong; can someone explain what's best for my sailing situation?

Thanks!
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Old 07-18-2007
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there is a very good reason for having a starting battery and house batteries and that is if you run the house batteries down you can still start the engine I would not ever be conected to the starting battery if you are not running or about to run the engine there are voltage regulating relays on the market that will cut power at a set voltage but I do not know as I would trust them on a long trip when it is so easy to flip a switch but they are a good backup plan as for starting off of deep cycle batteries some will produce enough amps to start your engine but are not desined for that also low amperage is hard an startes as it can cause arcing between the brushes and comutator if sufficant amiture speed is not produced.

Last edited by dodgeboatguy; 07-19-2007 at 12:02 AM.
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Old 07-19-2007
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Assuming that your charging cct also runs through your switch.. and that your switch is definitely "make before break".. then I would use the engine battery for the blower and to start the engine, leave it switched in for a specified charging time, and then switch to charge your house bank independently when you have the opportunity. I wouldn't charge to "both". Charging seperately gives you more control over where the energy goes.

Under normal conditions, starting the engine takes very little energy and does not need a long time to recharge.

House loads can certainly drag the battery down and so the house battery will require more charging time to replenish it. Use the house battery for all loads incl. instruments any time the engine is not running. Protect the starting battery from being run down at all costs. If you can start the engine, you can recharge.
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Old 07-19-2007
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Umm... you could always get one of these, which is a battery switch and a combiner. That way you wouldn't have to futz with the switch or risk blowing out your alternator.
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Old 07-19-2007
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If you are only sailing for a few hours at a time, it really doesn't matter. Unless you're running some big loads while sailing, a deep cycle or combination battery should not be run down from sailing for a few hours.

Run the blower and start off battery 1, leave it online to charge while the engine is running to take you out. Leave #1 on line while you're sailing to run instruments, etc. Use the same battery to run the blower and start the engine to bring you back in. Battery 2 is always in reserve on the outside chance that #1 gets run down.

Next time out, run on #2, keeping #1 in reserve.

You're charging with shore power also, right?

Now, when your aspirations to cruise start taking you away over night or for weekends , it might be time to look at what SD suggested.

I put in an ACR (60A) and dual circuit plus switch like shown here: http://bluesea.com/viewresource/69 with engine charging the starting battery (1100 MCA). A (50A) shore powered charger is connected to the house bank (450 Ah).

It makes battery management much simpler, turn the switch ON when I'm on the boat, turn it OFF when I leave. The set-up connects the house bank to the starting battery when charging, isolates them when they are discharging.

Last edited by CapnHand; 07-19-2007 at 09:36 AM.
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Old 07-19-2007
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Hey, is an alternator typically wired directly to the batteries, or to the selector switch?
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Old 07-19-2007
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geary126 - the alternator is usually wired to the starter which is wired to the selector output

jaschrumpf - keep it simple until you see the need to make it more complex. I can't imagine the blower draining that much so I wouldn't worry about. Put your switch on both before starting engine (the lower charged house battery will not drain the start any measurable amount). Then after shutting down the engine remember to go down and put the switch on house. (Forgetting to do this is one of the reasons people change the setup.)
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