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Old 17-12-2015, 08:55   #1
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Battery Bank Amp - Hour Requirements (Confused again)

I've read about how to size the battery requirements for our Pearson 35 Sailboat. It has minimal electronics (by design) and i am a bit confused about the sizing of the batteries.
Here is how i did may calculations (All Approx)
I listed all the equipment on the boat and calculated the total AmpH draw over a 24 hour period. That is my "typical" day of sailing and a night at anchor. That number is approx. 66 AmpH.
Then I ADDED to that the AmpH used if i also sailed at night (VERY RARELY). That number is approx. 87 AmpH. Higher because of radar use etc.
So my "worse case scenario is 153 AmpH Total draw.
My Batteries are rated at 105 amps/20 hrs....I plan to use THREE or a total 315 Amps per 20 hours.
My question...is this adequate and the right thinking.
Thanks
Bill
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Old 17-12-2015, 09:43   #2
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Re: Battery Bank Amp - Hour Requirements (Confused again)

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Originally Posted by Maine_bill View Post
... So my "worse case scenario is 153 AmpH Total draw.
My Batteries are rated at 105 amps/20 hrs....I plan to use THREE or a total 315 Amps per 20 hours ...l
Your 315 A/Hr battery bank can be discharged to no less than 50% (unless 'special' batts) capacity, giving you a maximum discharge of 157 A/Hrs prior to requiring a full recharge.
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Old 17-12-2015, 09:51   #3
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Re: Battery Bank Amp - Hour Requirements (Confused again)

And, you have 157 AH usable capacity the day you install them, in three months you will have lost some capacity, but your thinking and calculating, and that's good.
I'll admit myself to essentially just stuffing in as many batteries as I could reasonably fit, downside is cost and weight, upside is shallower cycling gives you longer battery life, and excess capacity give me more cushion before I have to start the generator. Means I run it longer, but less often of course, there is no free lunch.
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Old 17-12-2015, 09:53   #4
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Re: Battery Bank Amp - Hour Requirements (Confused again)

In theory you "should" get 24 hours before having to recharge in your worse case usage. Just keep in mind that the performance or total 20Ah capacity will diminish each year so by year 2 you will not get 24 hours of use in your worse case scenario.

What we need to know is:

-Are you planning on only 24 hour trips or less? Or are you going out for days on end?

-What means and rate of charging do you have available?

If you are only day sailling and will be plugged in each night or running a gen at night to charge then FWIW (worth: equaling free advice) then it looks decent to me.
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Old 17-12-2015, 09:56   #5
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Re: Battery Bank Amp - Hour Requirements (Confused again)

"My Batteries are rated at 105 amps/20 hrs....I plan to use THREE or a total 315 Amps per 20 hours."

They are actually rated at 105 Ah/20 hrs which means that you can get 105Ah if that energy is removed over a 20 hour period, which would be a rate of 5.25A.

It's good to avoid mixing up amps, and amp/hours.
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Old 17-12-2015, 09:56   #6
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Re: Battery Bank Amp - Hour Requirements (Confused again)

Yes, Gord is correct, PROVIDING that the batteries are new, installation is good, etc., etc.

We really can't answer your question properly without additional information.

1. What is your present battery setup? You mentioned "battery". Is that the only battery?

2, Do you have room for additional batteries? Where?

3. Are you planning to have a house battery bank separate from the starter battery? Do you even have an engiine? What type?

4. Do you have any onboard charging sources: engine/alternator, generator, solar, wind, etc.?

From what you've told us so far, I can only surmise that the batteries you're talking about are 12VDC typical 105AH batteries. The best alternative for house banks is generally 6VDC golf cart batteries in series/parallel. That's because these are more robust than 12VDC batteries, have thicker plates, and are true deep-cycle batteries.

Two golf-cart batteries would give you about 225AH capacity. Four would be better (450AH capacity) if you have room for them.

Bill
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Old 17-12-2015, 11:54   #7
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Re: Battery Bank Amp - Hour Requirements (Confused again)

Thanks ..tons of info
I'll try to answer your questions
My typical day of sailing and overnight anchorages will comprise approx 99% of our cruising. MAYBE one overnight. So 99% of the time my total AmpH use is about 66AmpH. I will have THREE 12volt 105/20h rated batteries for a total of 315/20h (more on the batteries in a minute)
I plan to have one battery as "starter", and two as "house" batteries. I will use all batteries for starting and charge all batteries while running the engine. When I shut down, for the night I run off just TWO batteries (210/20h).
I have no other options to charge at the moment. The other factor will be the ICW ...LOTS IF MOTORING to charge the batteries
I have room for another battery if needed ..FOUR TOTAL, but don't know I may run into charging issues with my current engine generator( no idea how big it is )

As to the battery issue I mentioned
You can purchase a Deep Cycle 105/20h battery from a well known Marine Store..the cost is $250.00 OR you can go to SAMs Club and buy a Duracell Deep cycle, same 105/20h battery...$95.00. Both batteries are manufactured by East Penn Manufacturing. The battery is DC31DT (east penn number). These batteries are IDENTICAL...Confirmed to me by the manufacture yesterday. So at the price that I can purchase them for ...I'm sticking with them

Hope I answered all the questions
Bill
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Old 17-12-2015, 12:16   #8
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Re: Battery Bank Amp - Hour Requirements (Confused again)

Bill,

OK, thanks for the info.

Your plan will work just fine. Suggest you use the one you've got for starting, and the new ones for house batteries.

Yes, battery pricing can be crazy.

May I suggest one thing. Be sure to have on had the following two tools:

1. a decent digital multimeter (Flukes are good; some others OK); and
2. a decent digital AC/DC clamp-on ammeter.

With these two tools you won't have to wonder what's going on. You can directly MEASURE what's happening in real time.

You don't have to pay an arm and a leg for the clamp-on meter. The Mastech MS-2108 (NOT the MS-2108A) can be had new shipped from CA for $66. This meter measures AC and DC current and has lots of useful features. I have two of them as well as a very expensive Fluke, but generally carry and reach for the Mastech first :-)

Bill
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Old 17-12-2015, 12:21   #9
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Re: Battery Bank Amp - Hour Requirements (Confused again)

If you can fit them, go with 6V golf cart batteries from Sams Club, especially for the house bank, you can still have one 12 v for the start bank if you like, but for actual cycling, the 6V batteries will give you much better service as that was what they were manufactured for.
The 12V battery even though the label may state deep cycle, isn't a deep cycle battery.

Best would be 4 6V Sams Club batteries, and I would run them as one big bank, but some disagree.
I figure managing battery charge is no harder than keeping an eye on the fuel gauge, if I can be trusted not to run out of fuel, then I can be trusted not to run out of battery.
But your going to find out that your stock Alternator is going to do a very poor job of charging batteries too
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Old 18-12-2015, 05:05   #10
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Re: Battery Bank Amp - Hour Requirements (Confused again)

I can suggest a shortcut approach, very little math required: install as much Ah capacity as you can fit in the available space, and then make your usage conform to that limit.


Part Deux: You may be able to fit 4x 6V golf cart batteries into a space not much larger than your 3x G31s. If so, the GC bank would give you approx. 440 Ah versus that 315 Ah from the G31s. AND the deep cycle (really) GCs would be more suitable for deep cycling than would be the "deep cycle" (or not) G31s.


Even if used for starting too, you'd have plenty of CCAs/MCAs for most sailboat auxiliaries.


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Old 18-12-2015, 07:47   #11
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Re: Battery Bank Amp - Hour Requirements (Confused again)

Almost every new boater/cruiser plays the game of how cheap and small a battey bank they can get away with and no nonfirst-hand experience or advice seems to change their mind (it didn't for me anyway). Then after having the too small bank die or from days of waking up to 12.1v batteries eventually seasoned cruisers realize the false savings in a "just but enough discount battery bank".

It's a learning curve the OP will have to go through himself...I played the Costco battery game myself and no one could have talked me out of the savings. It was experience that finally did that and I think on my 3rd set of new batteries.... Ha ha ha...I'm a slow learner.
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Old 18-12-2015, 08:29   #12
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Re: Battery Bank Amp - Hour Requirements (Confused again)

Quote:
Originally Posted by Maine_bill View Post
As to the battery issue I mentioned
You can purchase a Deep Cycle 105/20h battery from a well known Marine Store..the cost is $250.00 OR you can go to SAMs Club and buy a Duracell Deep cycle, same 105/20h battery...$95.00. Both batteries are manufactured by East Penn Manufacturing. The battery is DC31DT (east penn number). These batteries are IDENTICAL...Confirmed to me by the manufacture yesterday. So at the price that I can purchase them for ...I'm sticking with them

Hope I answered all the questions
Bill
Bill,

Yes they are the identical battery but the "Deep Cycle" sticker is misleading at best and a flat out lie at worst..

Regardless of what the sticker says flooded Group 24, 27 & 31 batteries are not a deep cycle product. Sure, they are "deeper" cycling than a starting battery they share a case size with, but they are still NOT deep cycle...

A 6V or 12V golf cart battery is where actual deep cycling capabilities begin in flooded batteries.

What Is A Deep Cycle Battery




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Old 19-12-2015, 07:22   #13
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Re: Battery Bank Amp - Hour Requirements (Confused again)

Thanks for all the advice...lot to absorb, but in the end I think I've decided on four (4) 6volt T105's ....

My next question ...
Will my current alternator be adaquate to charge them

I "think" it is a Motorola Y3N3S..rated at 37 amps...it was rebuilt by the PO in 2012
The engine is a 24 hp Universal

Bill
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Old 19-12-2015, 07:34   #14
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Re: Battery Bank Amp - Hour Requirements (Confused again)

37 amps is not even at 10% of the rated ah. I would say 15-20% of rated ah so you can charge from 50% of discharge and be able to run electronics comfortably. Also if you dont have a shore charger or other means of charging besides your alternator you are going to have to run the engine for really long periods of time to get over 80% charged.
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Old 19-12-2015, 07:42   #15
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Re: Battery Bank Amp - Hour Requirements (Confused again)

Quote:
Originally Posted by Maine_bill View Post
Thanks for all the advice...lot to absorb, but in the end I think I've decided on four (4) 6volt T105's ....

My next question ...
Will my current alternator be adaquate to charge them

I "think" it is a Motorola Y3N3S..rated at 37 amps...it was rebuilt by the PO in 2012
The engine is a 24 hp Universal

Bill
Good man...

You're on the path to righteous reserve!
The smarter boys will be back with the charging question...
But you are below the min 10%
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