Both Eric and Charlie have provided valid useful numbers. However, other data must be considered as well. I use my boat about once per week during the roughly 25 week season. So, even at 2000 cycles for the LFP batteries, I will be 140 years old when the batteries have used up their cycles. Does anyone know a typical life for these battery chemistries in years? Do they really last for their rated cycles even if it takes 80 years to do that many cycles?
I am currently using AGM, so I will only be 92 when 800 cycles are complete. (For those not good at math, I am currently 60.)
Pat
--- In electricboats@yahoogroups.com, "The_BearBoat" <cjohnson@...> wrote:
>
>
>
> --- In electricboats@yahoogroups.com, "Eric" <ewdysar@> wrote:
> >
> Here's some cost examples for the three types of batteries based on rated capacities:
> >
> > FLA (Trojan T-105) = $0.11/Wh (Wh = Ah x V, i.e. 100Ah 12V battery = 1200Wh)
> > AGM (Odyssey PC1800) = $0.25/Wh
> > Lithium (Thundersky LFP160AH + Simple BMS) = $0.45/Wh
> >
> > It looks like FLA are 1/4 the cost of Lithium for the same capacity.
> >
> > But as a boater, you know that you can't run consistantly batteries to fully discharged without adversely affecting their lifespan. Many people believe that FLA should be kept above 60% depth of dicharge (DoD), AGM should be kept above 70% DoD and LiFePO4 are rated for 3000 cylces to 80% DoD. So if we apply those guidelines to calculate cost for usable capacity we get something like this:
> >
> > FLA = $0.11/Wh rated divided by 60% usable = $0.183/Wh usable
> > AGM = $0.25/Wh rated divided by 70% usable = $0.357/Wh usable
> > LiFePO4 = $0.45/Wh rated divided by 80% usable = $0.562/Wh usable
> >
> > So looking at cost per usable Wh, FLA should deliver about the same range as Lithium for 1/3 the price. Lithium is only less than 60% more than AGM for the same range. The Lithium batteries weigh about 60% less than FLA or AGM for the same range.
> >
>
> Eric-
> Good analysis. I suggest to really perform an apples to apples comparison that the life cycle cost needs to be calculated. Assuming the following discharge/charge cycles:
> FLA: 500
> AGM: 800
> LFP: 2000 (mfgrs. are stating 3000, but...)
>
> and using your figures for cost per usable Wh yields the following cost/usable Wh/cycle:
>
> FLA: $3.66 x 10^-4
> AGM: $4.46 x 10^-4
> LFP: $2.81 x 10^-4
>
> Consider the maximum charging rates is also enlightening:
> FLA: 0.2C
> AGM: 1.0C
> LFP: >1.0C
>
> LFPs are NOT plug and play. They take relatively intense involvement by the operator to ensure maximum cycle life and safe operation. However, in the cases where high discharge rates, large capacity, and minimized footprint and weight must be considered, they are a game changer.
>
> Charlie
> JTB Marine Corporation
>
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