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 only 2.3 times the cost of 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.
------------------------------------
Another point to consider is that the math is dependent on the load. Because of Peukert's Effect, higher capacity/load ratios favor Lithium, but lower capacity/load 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
--- In electricboats@yahoogroups.com, "epowermarine" <todd@...> wrote:
>
> I agree that comparing in watts is much easier and more realistic than talking amp hours, which is only relevant in the context of voltage.
>
> To try and take this out a little further we need to do some more computing to make these numbers a more direct comparison. Specifically we need to account for 3 more variables: the Puekert coefficient, battery design life, and also the safe depth of discharge level. The problem is that all three of these values are a bit squishy, and/or up for debate as to what the correct value is.
>
> Let's say you buy an Odyssey AGM battery. Under normal cycling they will tell you that the design life is about 10 years. Other AGM vendors might say 5 years. Some Lithium manufacturers will say 10 year design life. Flooded is more like 5 or so. How many years you actually get will of course be determined by how you use/care for them. It is quite likely that you would go through 2 sets of Flooded or inexpensive AGM's to one set of Lithiums. That would increase your cost per watt hour over a 10 year period by a factor of 2.
>
> 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.
>
> So, at the higher rates of discharge that my boats typically operate at the cost per watt hour among the different types really start to converge. Flooded and AGM get more expensive, and Lithium choices seem more in line with the lead acid choices. Now we are looking at cost per "USABLE watt hour" numbers and can make smarter decisions on what would work for a particular application.
> Capt. Todd
> www.epowermarine.com
>
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