Hi Don,
I'm not sure what physics lesson that you're looking for, but here is a detailed comparison between battery chemistries by cost, weight and range.
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This is what I posted on April 20 this year in post #21398
"Hi Capt. Todd
Perhaps you mean something like this post that I made back in Jan 2012 (post#20750) and reposted in this month (post #21237). I directly compared the weight and cost of the same usable capacity of different battery types. Peukert's has already been factored in. You can read the whole post here http://groups.yahoo.com/group/electricboats/message/21237
You said "Additional concerns are that the estimated Puekert coefficients might be 1.0 for Lithium, 1.1 for AGM, and 1.3 for Flooded. Estimated safe discharge levels might be 80% for Lithium, 60% for AGM, and 50% for Flooded."
In case you want to check my math, for my calcs I used a PE of 1.03 for Li (no battery is 1.0), 1.1 for AGM and 1.25 for FLA. And you can see that I used discharge levels of 80%, 70% and 60% respectively.
-- Excerpt from post #21237 -----------------------------------
Let's do the math for a battery pack that has a usable 2.5 hour range at 2500W (6.25kWh used).
FLA – 14.25kWh to 60% DoD at 2500W = 2.5 hours = 633 lbs, cost about $1500
AGM – 10.5kWh to 70% DoD at 2500W = 2.5 hours = 520 lbs, cost about $2500
LiFePO4 – 8.25kWh to 80% DoD at 2500W = 2.5 hours = 200 lbs, cost about $3500
So now the lithiums are 2.3 times the cost of the FLA T-105s but they are less than 1/3 the weight for the same range at this load. So for most boaters, I recommend AGMs as a good balance of price to range.
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Another point to consider is that the math is dependent on the load. Because of Peukert's Effect, higher load/capacity ratios favor Lithium, but lower load/capacity ratios make AGM and flooded look better. Aiming for the same amount of energy consumed, here's a similar chart at 4000W for 1.5 hours (6kWh used)
FLA – 15.1kWh to 60% DoD at 4000W = 1.5 hours = 670 lbs, cost about $1600
AGM – 10.5kWh to 70% DoD at 4000W = 1.5 hours = 520 lbs, cost about $2550
LiFePO4 – 8kWh to 80% DoD at 4000W = 1.5 hours = 200 lbs, cost about $3400
Here's the another chart at 1500W for 4 hours (6kWh used)
FLA – 12.5kWh to 60% DoD at 1500W = 4 hours = 550 lbs, cost about $1350
AGM – 9.6kWh to 70% DoD at 1500W = 4 hours = 475 lbs, cost about $2350
LiFePO4 – 7.8kWh to 80% DoD at 1500W = 4 hours = 195 lbs, cost about $3300
Looking at 6kWh usable at both 4000W and 1500W, we can see that FLA cost 40% of Li at 1500W and 47% of Li at 4000W, mostly because of Peukert's Effect. You can see where this is trending.
I haven't even thrown battery life into the mix, but since I'm still working I don't put as many cycles into my boat as I would like. With proper maintenance and charging, I believe that I could get all of these battery banks to last 10 years. But that's just the way that I use my boat. For someone that cycles their pack more often, replacement cost may need to be factored in.
I hope that this helps.
Fair winds,
Eric
Marina del Rey, CA
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--- In electricboats@yahoogroups.com, donald bland <dlblandjr@...> wrote:
>
> so to answer you retoric question , sounds great , cept , I think I need 48 v ,
> for a E.Y. system as I understand it .
> so . . . we have Mike , and George , whom we can , thankfully ask , for a wee
> physics lesson then mates!
> perhaps maybe this other fellow, Aaron Vivian , will sign in as he said he would
> and further enlighten our little minds , eh ?
> weeel , I must indulge my better half in going out to dinner , so we must resume
> this convo on the morrow , eh mates?
>
>
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