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post #30 of Old 11-20-2012
Maine Sail
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Re: Battery Sizing - am I crazy?

Originally Posted by asdf38 View Post
Right and I don't have any numbers to quantify life. And while I've heard people say that GC's last longer I've remained skeptical for three reasons:
1) It's said that because they have less cells the plates are thicker. Fine but you could realize the same benefit by moving to larger 12V batteries. I've never seen/heard evidence of that.
Actually you can't the plates are still thinner, on average 0.040 - 0.065 vs. .100 - .125, and footprint is again one of the biggest limiting constraints.

Originally Posted by asdf38 View Post
2) The weight numbers I just ran through came out nearly 100% identical energy density by weight for the GC vs the 12V. That suggests, though doesn't prove, identical technology internally. (The volume numbers differed but volume factors in non-functional aspects like case design).
Again, energy density is a totally meaningless figure because it does not take life cycles into account. You can have a 100Ah battery rated at 200 cycles and a 100Ah battery rated at 2000 cycles... No comparison..

Originally Posted by asdf38 View Post
3) The applications are largely the same - why would Deka engineer better cycle life into their GC batteries than their marine batteries.

So do you have any data to point too on this?
Actually the "applications" are not the same. For years the marine industry has used "hybrid" dual purpose style batteries that by true deep cycle definition are not really deep cycle batteries at all. They do make true deep cycle 12V batteries but your not buying them at WM or most marine stores.. Do they work? Sure, are they as optimal as 6V or 2V cells for a marine deep cycle application in terms of longevity, absolutely not..

So as for data yes I have hundreds of boats I work on, in the "real world", that show a 20 - 40% longer average life with 6V vs. 12V. I use the best analyzers money can buy, one is $2000.00 and the other was about $800.00 plus I have many other means of testing too. My Midtronics tool is the one battery manufacturersuse and supply to distributors like West Marine, Wal*Mart & Sam's Club for warranty claims.

Beyond that data you can always call Trojan and ask them for the cycle life at 50% DOD for the marine SCS series of 12V batteries vs. the Golf Car line. What they will tell you is that the SCS at 50% DOD is rated by Trojan at 600 cycles and the golf car batteries like the T105 are rated at 1200 cycles!!! Of course these are "lab" numbers and you'll never see that in the "real world" but you will see longer life out of 6V golf cart batteries vs. 12V in the same application.

Again that is DOUBLE THE CYCLE LIFE, per Trojan battery.... So yes the thicker plates, case design etc. do make differences. Remember that 6V battery has 3 cells and weighs 66 pounds vs. the 12V battery having 6 cells and weighing the same. Which battery has the thicker plates the one with 3 cells or the one with 6 cells?

I don't see the 50% differences in the "real world" but I do see 20-40% longer life "on average" out of true deep cycle golf car batteries vs. 12V "marine style" batteries.I measure this with industry standardized test equipment so this is not just a shoot from the hip thing... The differences are real, quantifiable and measurable differences and also backed up by companies like Trojan battery in their own in-house testing.

You can choose to believe or not... I see, touch, feel & measure so I believe....

-Maine Sail / CS-36T

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