one 8D batterie...enough? - SailNet Community

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Old 06-03-2010
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one 8D batterie...enough?

I was going to use 3 deep cycle, but I have the perfect spot for one large 8D.
this batterie will be charged by inbord diesel and solar. my power needs are limited to radio, lights and autopilot.

will it do the job?
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Old 06-03-2010
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It really depends on what your usage is. What are you currently using? Do you have a battery monitor that gives you data on past usage? If not, you will need to predict your usage by determining how much time each day you plan to use these things in the worst case scenario.
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Old 06-03-2010
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Lightbulb Please consider two sixes...

Quote:
Originally Posted by jobi View Post
I was going to use 3 deep cycle, but I have the perfect spot for one large 8D.
this batterie will be charged by inbord diesel and solar. my power needs are limited to radio, lights and autopilot.
will it do the job?
You will need to do some calculations to see if the amp hours in an 8D (or equivalent) will suffice, but one caveat is that if that is indeed the right size... then install two golf cart batteries instead.

The single 8D is frightfully heavy. Even each golf cart battery, at about 80# per, will be quite a load to lift aboard and place into your chosen location. I have a pair of Trojan T-145's, and was very glad to have some help to schlep them aboard and lower 'em into the battery box.

L
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The other piece of the puzzle often ignored is the charging system. Your battery bank, regardless of what you choose, has to be recharged or it quickly becomes useless. also, it should routinely be fully recharged or you will severely shorten it's useful life.

Let's assume, as you didn't say, that you have a stock 80 amp alternator as your only charging source. It outputs realistically 30 amps except for short periods at the beginning and end of a recharge. If you run a 400 amp bank down 50% over some period and use this as your charging source, it would require approx 10 hours of engine time to completely recharge - these are gross numbers. If you don't completely recharge, your useful battery cap is reduced accordingly.

So, you can see choosing a battery size or sizes is dependent on more than one consideration. A battery is part of a system, not an isolated component.
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The standard wisdom is that if you have only alternator charging you will only get 80 to 90 percent recharged anyway. So a 100 amp battery may only have 80 amp available.
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Old 06-04-2010
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golf chart batteries, arent these things 6v?
why use them, I mean what advantage do they offer.

ok I did mention my batteries will be solar (80w) charged and by inboard engin. my power needs are lower then most pepoles use, no tv, pc, no fridge.
I guess my question is if one large batterie was better then 3 smaller batteries.
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Old 06-04-2010
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Quote:
Originally Posted by jobi View Post
golf chart batteries, arent these things 6v?
why use them, I mean what advantage do they offer.

ok I did mention my batteries will be solar (80w) charged and by inboard engin. my power needs are lower then most pepoles use, no tv, pc, no fridge.
I guess my question is if one large batterie was better then 3 smaller batteries.
Golf cart batteries are 6 V - two in series produce 12V, four in parallel/series configuration is 12V at double the capacity.

A battery is a combination of 2V cells. A hundred batteries is a combination of 2V cells. It's the same thing - just different size and capacity!

There are a number of good basic boat electrical books around which might give you a better understanding...
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Batteries do fail, so being paranoid, I'd rather go to a pair of 4Ds or multiple batteries. If the 8D fails, you're in trouble. If you've got a couple, you can isolate the defective one and still enjoy the sail.

To me, the best thing about 6V "golf cart" batteries aside from the cost and weight, is that you don't lose a 12V battery if you have a failure. You lose 1/2 of the 12V bank and getting a 6V battery can be significantly cheaper than buying a 12V one.
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Old 06-04-2010
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Quote:
Originally Posted by jobi View Post
golf chart batteries, arent these things 6v?
why use them, I mean what advantage do they offer.

.
Trojan now makes a 12v golf cart battery. T1275. Very nice if you do not have the height to have 6v batteries. The T1275 height is the same as a 4d or 8d.
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Old 06-04-2010
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hey thanks guys, it all makes sens now!!
cheers
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