T-Pain Is On A Boat: Re: [Electric Boats] Re: Batteries

Friday, June 11, 2010

Re: [Electric Boats] Re: Batteries

My $0.02 on "safe" depth of discharge:

For lead acid batteries, at least, their life is a function of dod, deeper cycles mean shorter life.

What does this mean in real life? Look a the battery tech manual on Concorde-Lifeline's web site. Page 35 shows 1000 cycles at 50% dod; 500 cycles at 80% and 350 cycles at 100%. Discharging to 100% once in a while isn't "not safe". Even 350 cycles is once a week for 5 years.

Also, the peukert exponent of the battery is an important part of the comparison because the capacity at a C20 discharge rate is not very relevant to an application where C5 or even C2 or C3 is typical. Dig into the mfr's data and you can usually find capacity at these high rates.

Denny Wolfe

www.wolfEboats.com

----- Original Message -----

From: John Francis

To: electricboats@yahoogroups.com

Sent: Friday, June 11, 2010 5:32 AM

Subject: Re: [Electric Boats] Re: Batteries

Eric

Do you know how/if active discharging has any worthwhile effect on the the purchase of batteries?

I've heard that LiFePO4 batteries can be virtually disharged to near dead, AGM batteries can discharge down to about 30% +/- and that flooded batteries can safely discharge to about 70%.

Would this mean that, relatively speaking regarding the preceding sentence, a 100 AH battery would offer about 90AH +/-,(LiFePO4), 70AH +/-(AGM) and 30AH +/-(Flooded)?

If so, then the added costs of LiFePO4 batteries begin to look really worthwhile inas much that less capacity, could actually mean more available power(?).

John Francis

On Thu, Jun 10, 2010 at 8:26 PM, Eric <ewdysar@yahoo.com> wrote:

David,

This topic gets discussed often. Do a search in this Yahoo group using "agm wet battery capacity" and you'll get some very detailed answers. There are other posts but there are so many posts that cover parts of your question, it's hard to narrow down the list.

The very short version is the following:
All lead acid, flooded, AGM, Gel, etc. weigh close to the same per kWh of storage, Lithium (LiFePO4) is about 40% the weight of lead acic.

Flooded cells are cheapest, AGM up to twice the cost, and LiFePO4 about twice that.

AGMs and LiFePO4 have very low self discharage rates.

AGMs have a longer lifespan than flooded, LiFePO4 longer still.

They are all safe. Most people don't consider Gels worth the price for our purposes.

Try to dig deeper into previous posts here and the best of luck in your conversion.

Fair winds,
Eric
Marina del Rey, CA

--- In electricboats@yahoogroups.com, "davidhughes_casaba" <davidhughes_casaba@...> wrote:
>
> I will be installing a 24 volt direct drive system and I am researching my battery options. So many combinations to choose from and wanted to get some feed back from this group and it not just on cost, but safety, longevity, weight, charging consideration, self discharge rates, ect. I was looking for about 200 amp hours and my first thought was 2 4D AGMs but man those 4Ds are big and heavy, the battery boxes for those are also very expensive. The 4D AGMs are also a chunk of change.
>
> Any feedback on Wet Lead Acid, versus AGMs, Gels, or other metal hybrids would be interesting as well as thoughts on 2 12v 4Ds, 4 6 volt, 4 12 volt group 31's (to get the individual weight down).
>
> Thanks
>
> Dave
>

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