T-Pain Is On A Boat: Re: [Electric Boats] Re: Battery Life and Types

Thursday, September 16, 2010

Re: [Electric Boats] Re: Battery Life and Types

Jim for LOW power lead acid cannot be touched. That is what they were made for. Golf carts that run only limited time over a long period. This works out well for the big heavy lead acid batteries because they have time in between run time to recoup. Golf carts would not go as long if you just got on them and ran them non stop. This also works well for the boater that only need it to get in and out of the marina. OUT rest it until you get back 5 hrs later then IN. Charge it. Lead Acid has the low up front cost.

LiFePo are for constant use at full power. They do not need to rest to recoup. They have a large up front cost. It is like buying a new car you better make sure you are going to use it till it falls apart or you will never get your money back. What Eric was saying in the long run each battery cost about the same and LiFePo has some advantages in power. On the other hand IF you take very good care of a lead Acid you can get great usage out of it, but not as much power. If you need the power for motorsailing LiFePo is a better fit. If you just need to get out of the marina and you use your electronics while out, Lead Acid is a better fit. Then you also have to look at weight. If you took an engine out you need to replace that weight. Either by more lead ballast or about the same weight in batteries. Another option would be to move some weight from up front to the rear. (Water tanks). Remember you now do not have any fuel tanks in the rear even more weight gone.

Dan

--- On Thu, 9/16/10, luv2bsailin <luv2bsailin@yahoo.com> wrote:

From: luv2bsailin <luv2bsailin@yahoo.com>
Subject: [Electric Boats] Re: Battery Life and Types
To: electricboats@yahoogroups.com
Date: Thursday, September 16, 2010, 4:08 AM

Good stuff there Eric. It will take me a while to digest it all, but it looks reasonable. I think you may be a little pessimistic in assuming 250 cycles to 60% for the T-105s, but I don't have any hard data to back up that assertion. At any rate, the general sense sense I'm getting is that for lower power applications lead-acid compares favorably cost-wise, but there is a weight penalty. As you get above a few HP the balance tips in favor of LiFePo. Looks like they are pretty close in the 2KW range where I tend to operate much of the time, and the lower up-front cost is a definite advantage for me. Thanks for the insight.
Jim

--- In electricboats@yahoogroups.com, "Eric" <ewdysar@...> wrote:
>
> Jim,
>
> I'm not sure what number that you're looking for, but here's a bunch of data comparing my battery bank to a set of T-105s.
>
> 8kWh bank of LiFePO4 batteries, cost $3600 including BMS, tax and shipping, weight 200 lbs. Manufacturers lifespan is > 2000 cycles at 80% DoD.
>
> Assuming 1 deep discharge per week for 10 years:
> 6400Wh x 500 cycles = 3,200,000Wh delivered
> 3200kWh / 200 lbs = 16kWh/lb
> $3600 / 200 lbs = $18/lb
> $18 / 16kWh = $1.125/1000Wh delivered
>
> From what I know about Trojan T-105s
> 11.25kWh bank of 8 T-105 batteries, cost $1200 including tax and shipping, weight 500 lbs. Manufacturers lifespan is less than 500 cycles at 60% DoD.
>
> Assuming 1 deep discharge per week for 5 years:
> 6750Wh x 250 cycles = 1,687,500Wh delivered
> 1687.5kWh / 500 lbs = 3.4kWh/lb
> $1200 / 500 lbs = $2.4/lb
> $2.4 / 3.4kWh = $0.70/1000Wh delivered
>
> But these numbers aren't the whole story. Because of the different battery chemistry and Peukrert's Effect, T-105s deliver much less energy under load than the Li batteries do. Assuming a 2kW load, the T-105s should deliver 4920Wh in a 60% DoD cycle, the Li batteries will deliver 6100Hh in an 80% DoD cycle. Here's the same calcs again:
>
> Assuming 1 deep discharge per week for 10 years:
> 6100Wh x 500 cycles = 3,050,000Wh delivered
> 3050kWh / 200 lbs = 15.25kWh/lb
> $3600 / 200 lbs = $18/lb
> $18 / 15.25kWh = $1.18/1000Wh delivered
>
> Assuming 1 deep discharge per week for 5 years:r
> 4920Wh x 250 cycles = 1,230,000Wh delivered
> 1230kWh / 500 lbs = 2.46kWh/lb
> $1200 / 500 lbs = $2.4/lb
> $2.4 / 2.46kWh = $0.98/1000Wh delivered
>
> So for this usage pattern, the lithium batteries cost 20% more per delivered watt hour but are only 40% the size and weight of the T-105s.
>
> I don't know how relevant these numbers are, since they are based on a broad set of assumptions, but those assumtions are stated here. Change the assumptions and the results will change. From my perspective, this is a fair comparison.
>
> Fair winds,
> Eric
> Marina del Rey, CA
>
> --- In electricboats@yahoogroups.com, "luv2bsailin" <luv2bsailin@> wrote:
> >
> > Right on Steve, but I suggest running them down more to increase range without increasing weight. If you only go to 50%, then half that lead is just ballast. Even if they only last 5 years, that's about $200 per year at today's prices. I'm sure most power boaters spend more than that on maintenance.
> > It would be interesting to compare cost per pound per cycled watt-hour or some such bench-mark for various usage patterns. I know there are a couple spreadsheet gurus on this site...
> > Cheers,
> > Jim McMillan
> >
>