T-Pain Is On A Boat: Re: [Electric Boats] FLA vs AGM vs LiFePO4

Monday, August 26, 2013

Re: [Electric Boats] FLA vs AGM vs LiFePO4

Here is a re-run of a post that I made on Feb 21, 2013 that compares the three major options in batteries. You'll notice that I tend to use watts instead of amps or amp hours. Since even this thread has already included three different system voltages, using amps means that you've got to do math in your head to make any meaningful comparison.

The prices still seem to be close enough, the lithium prices include passive BMS modules like the ones in my battery pack (less than $300 for 16 independent modules)

Here it is again:

With all the recent talk about FLA vs AGM vs LiFePO4, I think that this post
(#22145 from Sep 6, 2012), provides a fairly good comparison of battery banks
that can deliver the same amount of work. This is as close as I've been able to
get to an "apples to apples" comparison.

You might want to look at the pics in the group folder "Eric's Serenity".
http://groups.yahoo.com/group/electricboats/photos/album/1967401930/pic/list
The last pic is half of my 160Ah 48V traction bank. Lithium is not only
lighter, it is considerably smaller than either FLA or AGM. Weight and size
were high priority when I designed my system.

Fair winds,
Eric
Marina del Rey, CA

--- In electricboats@yahoogroups.com, "Eric" <ewdysar@...> wrote:
>
> ---------------------------------------------
> This is what I posted on April 20 this year in post #21398
>
> 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 T-105 FLAs 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 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, entirely 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
> -----------------------------------
>
>