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Old 09-10-2017, 12:40   #1
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Reducing size of battery bank

I have charging issues. 85amp alternator and 80w solar panel aren't charging my 3 Trojan scs225 (130A) batteries on my sailboat.
My solution has been to order 3 bigger capacity batteries but this week we spent 8 days on the hook with the old batteries and I directed all recharging into one battery and used it for house and cranking with the other 2 as backup.... and survived fine.
So maybe this is a case of less is more... am I missing something here?
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Old 09-10-2017, 12:41   #2
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Re: Reducing size of battery banj

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I have charging issues. 85amp alternator and 80w solar panel aren't charging my 3 Trojan scs225 (130A) batteries on my sailboat.
My solution has been to order 3 bigger capacity batteries but this week we spent 8 days on the hook with the old batteries and I directed all recharging into one battery and used it for house and cranking with the other 2 as backup.... and survived fine.
So maybe this is a case of less is more... am I missing something here?
Bank not Bank... sorry
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Old 09-10-2017, 12:49   #3
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Reducing size of battery bank

Yes, your missing something. I donít mean that to be flippant, but I can think of no case except maybe to reduce weight where reducing a banks size is the right thing to do
My guess is one of your batteries is toast, a battery with a shorted cell will never charge, and will drag the rest of the bank down with it.
An 85 amp alternator if given enough time will recharge a 1000 AH bank or a 100 AH bank, its the amount of time that is a variable, but due to battery acceptance rates, it may not take much if any more time to recharge a huge bank than a tiny one.
Or said another way it takes about 5+ hours on average to fully recharge a battery.
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Old 09-10-2017, 13:10   #4
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Re: Reducing size of battery bank

Going to a bigger bank won't help either.

How much time do you spend away from shore power charging?

What is your average AH per day usage?

No matter your bank size, in the end your charge sources must put back in a bit more than you take out. Sooner you get back to 100% the longer your bank will last.

What a bigger bank does is help you avoid going down below 50% too often.

Very few alt / reg setups output a proper charge profile for a deep cycle bank out of the box.

Many don't even let you adjust the voltage setpoints or Absorb hold time, need to switch to an external regulator like Balmat MC-614, or fit a "battery to battery" DCDC charger like Sterling or ProMariner.

Same with old or cheap solar controllers.

80w won't do much if you use a lot of AH per day, really only good for the low amp "long tail"

You need to get the bank to 80-85% in the early morning first using dino-juice. Or get a lot more solar.
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Old 10-10-2017, 09:30   #5
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Re: Reducing size of battery bank

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Originally Posted by a64pilot View Post
Yes, your missing something. I donít mean that to be flippant, but I can think of no case except maybe to reduce weight where reducing a banks size is the right thing to do
My guess is one of your batteries is toast, a battery with a shorted cell will never charge, and will drag the rest of the bank down with it.
An 85 amp alternator if given enough time will recharge a 1000 AH bank or a 100 AH bank, its the amount of time that is a variable, but due to battery acceptance rates, it may not take much if any more time to recharge a huge bank than a tiny one.
Or said another way it takes about 5+ hours on average to fully recharge a battery.
A battery being " toast " would be my take also.
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Old 10-10-2017, 09:37   #6
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Re: Reducing size of battery bank

Nobody wishes they had less battery power. They might wish they had less weight (LiFePo4), but never less power/capacity.
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Old 10-10-2017, 20:38   #7
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Re: Reducing size of battery bank

I'm with john61....all right on. After cruising years on 4 6 volt batteries we are now cruising with 2 Lifeline 6 volt batteries for the house bank and a single 12 volt AGM battery for the starter. We have 240 watts of solar only and do not need the 135 amp Balmar alternator unless it is cloudy for several days. Of course, we have no appliances requiring an inverter.
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Old 10-10-2017, 20:53   #8
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Reducing size of battery bank

He got by with one 130 AH battery for eight days.
We can infer that whatever his consumption is, it was likely well less than 100 AH overnight, or he would not have enough battery charge left to crank the engine?
Actually well less than 100 AH as itís unlikely he recharged fully each day, so his one battery was walking down in charge likely every day.
Pretty small useage I bet.
80W isnít much, but first to make any sense of what to do, he needs to know what his consumption is.
May take is to spend the $$ upgrading Solar first. Big alternators and Balmar 614ís donít come cheap and you can buy a lot of Solar for what those cost, but if you regularly motor almost every day, then of course the alternator route makes a lot fo sense.
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Old 11-10-2017, 02:51   #9
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Re: Reducing size of battery bank

Thanks. We're not big consumers. Full led interior lights. Freezer runs off compressor powered by engine. 30 mins is enough per day. Windlass, fresh water pumps and starting engine are biggest draws. Charging kids phones is a constant but not huge draw.
Upgrading solar is doable. Getting batteries tested via full charge and draw down this week.
Rough calculation is using absolute max of 80amp per day.
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Old 11-10-2017, 03:34   #10
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Re: Reducing size of battery bank

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Originally Posted by nzmal View Post
Thanks. We're not big consumers. Full led interior lights. Freezer runs off compressor powered by engine. 30 mins is enough per day. Windlass, fresh water pumps and starting engine are biggest draws. Charging kids phones is a constant but not huge draw.
Upgrading solar is doable. Getting batteries tested via full charge and draw down this week.
Rough calculation is using absolute max of 80amp per day.

That's Amp hours per day, not amps per day.
(It helps if we all use correct units when discussing electrical needs - you may like to take a look at http://www.cruisersforum.com/forums/...ml#post1933764)

That said:

You 80W panel is likely to be giving you about 30 Amp hours per day, So you need to generate another 60 Amp hours or so to get your batteries back up every day.

Your 80 Amp alternator will not be putting 80 Amps into your batteries. You would probably need to run your engine for a couple of hours first thing in the morning, followed by the solar's 30Ah during the day if you have use 80Ah in the previous 24 hours.

If you've got the room, the best thing would be to triple your solar, and make sure you have a couple of hundred Amp hours of batteries.

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