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  #11  
Old 11-19-2012
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Re: Battery Sizing - am I crazy?

Quote:
Originally Posted by chartscharts View Post
My sailing habits are almost exclusively day sailing. 2-3 times a year (on good years) I'll take it out for an overnight. I could use battery powered camping lanterns on those even, since it's not very often.

-Charts
I dont think you need a deep cycle battery at all.

I dont think you need 2 batteries.

I think you need one quite small battery, like a 55 amp hour one. I dont know what they call them in the USA. But one small, good battery. Walmart or some other large auto store brand battery should be fine.

I just looked up a thing and it said Group 29 is 115 amp hours. I really dont think you need anything like that whatsoever. I suggest HALF that size.

For your overnight trips , as you say, take a camping lantern etc. If you sail overnight and the battery gets low just bung on the engine for a bit and charge it
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Old 11-19-2012
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Re: Battery Sizing - am I crazy?

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Originally Posted by MarkofSeaLife View Post
I dont think you need 2 batteries.
You definitely want a deep cycle. Deep cycles can start all day long with no harm. Starting batteries however have limited capacity and very bad lifetime if they are ever deep cycled.

Even a small Group 24 deep cycle can start that 1 cylinder engine with ease and will then have far more capacity for running the radio/lights after that.
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Old 11-19-2012
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Re: Battery Sizing - am I crazy?

Unless you have the option of hand starting your engine, I'd go with two automobile size deep cycles on a selector switch. Alternate them for starting the engine and switch to one only for house use - then if it dies you'll still be able to start your engine in the morning.

Switching to LED lighting will help a ton as well.

I know Deep Cycle batteries are not supposed to be starting batteries but I've used them that way and got nine years out of one $75 one with no problems.
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Old 11-19-2012
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Re: Battery Sizing - am I crazy?

Better not to short yourself and not have enough power should you want to add things on the future

I would go with 4 golf cart batteries deep cycle. These way about 45 lbs each and are easily manuevered by one person. 2 of these is about the same footprint of a group 31. Four would be the same size almost as 1 of you 8Ds with the same amp hours of 2 8ds

4- 6 volt golf carts =440 ah = 220 usable ah. Refrigeration should you ever add it will run between 50-75 ah a day.

Better to have to much than to little IMHO.

Dave
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Re: Battery Sizing - am I crazy?

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Originally Posted by SloopJonB View Post
I know Deep Cycle batteries are not supposed to be starting batteries but I've used them that way and got nine years out of one $75 one with no problems.
Not true...

Starting used as deep cycle = BAD
Deep cycle used as starting = No prob

Essentially the ONLY advantage to starting batteries is that they have more cranking camps for a particular size/weight. Given the deep cycle need for a usual boat versus it's engine size however there is usually no need for the extra CCA's.

From another thread:
Quote:
Originally Posted by Main Sail
Trojan Battery does an excellent job:

"Q: Can I use my Deep Cycle battery as a starting battery?


A: Deep cycle batteries can be used for engine starting but starting batteries should not be used for deep cycle applications. A deep cycle battery may have less cranking amps per pound than a starting battery, but in most cases a deep cycle battery is still more than adequate for the purpose of starting an engine."
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Re: Battery Sizing - am I crazy?

Yes, but read the ops post

He is NOT going to deep cycle the batteries.
He is only using them to start. He's taking a camping light. No refrigeration.
Where, tell me is there deep cycle in his elec usage?

There's not.

Read his post.
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Last edited by MarkofSeaLife; 11-19-2012 at 04:46 PM.
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Re: Battery Sizing - am I crazy?

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Originally Posted by MarkofSeaLife View Post
Yes, but read the ops post

He is NOT going to deep cycle the batteries.
He is NLT sing them to start. He's taking a camping light. No refrigeration.
Where, tell me is there deep cycle in his elec usage?

There's not.

Read his post.
And the flip side of that question is what advantage does the starting battery have?

If it has 6x the CCA requirement of the engine the answer is very little. Meanwhile those extra unused CCA's come at the expense of Ah's that can actually be used for lights and the radio. On top of that the design compromises that squeeze out the extra cranking amps severely reduce the lifetime of the battery when it's deep cycled.

Starting batteries are essentially tailored for cars which 1) Have giant engines for their size which need lots of CCA's and 2) run the engine 99% of the time they're used.

By contrast, sailboats go days between charges and have lights and radios which over a couple days of cruising can easily use up 20-40% of a smallish bank (especially if they're not LED). I just have a hard time seeing a use-case constructed where the starting battery is a better choice.
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Last edited by asdf38; 11-19-2012 at 05:18 PM.
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Old 11-19-2012
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Re: Battery Sizing - am I crazy?

Quote:
Originally Posted by MarkofSeaLife View Post
Yes, but read the ops post

He is NOT going to deep cycle the batteries.
He is only using them to start. He's taking a camping light. No refrigeration.
Where, tell me is there deep cycle in his elec usage?

There's not.

Read his post.
Actually, I did reread after this post, YOU need to reread the post, This sentence does stand out as not only needing to start the motor, but run on occasion the running and house lights, along with CB radio!

"My needs are modest. It primarily needs to start my Farymann A30, single cylinder, 10HP diesel. I have the usual running lights and house lights and VHF radio."

Reality is, he "could" get away with a single dual purpose battery, or two dual or Deepcycle batteries, or a single ea starting and house battery! The best option no matter how one slices it, is two batteries, not a single one. If the house, running lights, CB etc drain the batter too low, he will not start his engine! Hence why most of us will recommend 2 separate use batteries.

Now if one wants to argue about the size of ea, I'm not going there! as that has too many variables that come into play! Some would say his current 2 8D bats are too little! others a single size 24 75ahr battery is plenty for a house bank!

marty
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Old 11-19-2012
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Re: Battery Sizing - am I crazy?

I survived with no problem with two Group 27 deep cycles on my previous 30 footer with a 2-cylinder Universal diesel. Even on 2+ week cruises. Current boat has two Group 31 deep cycles and also fine with similar usage. They start my Yanmar 3GM with no problem. You could go with one starting and one deep cycle, but I would just go with two the same to keep things simple.
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Re: Battery Sizing - am I crazy?

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Originally Posted by Siamese View Post
I would typically suggest a bank of two 6v golf cart batteries and a 12v starting battery for emergencies, but for the needs you stated, a conventional lead acid deep cycle battery will serve you well. Keep some distilled water on board and top off the battery regularly.
Agreed. The advantages to the 6V GC batteries are high AH rating for their size and cost, full deep-cycle capability, a smaller footprint that gives you some mounting flexibility, and an easier job installing and removing them. Sam's club also sells GC batteries, as does Batteries Plus.

I agree you would do fine with a conventional 12V battery, but at least spec out a pair of GC batteries, you may find that works better for you.
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