Hey Ben,
Sorry for the confusion. Like others have said a T-105 is 225Ah x 6V. I only used the 100Ah x 12V as a simple math example to show Wh to those who might not know the conversion.
So it's been recommended that you should have a 400Ah x 72V pack? That's 28.8kWh. Very few people think in usable capacity when talking about batteries, so I would guess that they're talking about rated capacity.
I've seen a couple of boats and quite a few cars with battery banks between 25 and 30kWh and it's not quite as bad as you think. For example, 24 T-105s would be 450Ah x 72V (32.4kWh) and weigh about 1500 pounds. Similar range would be available from 48 160Ah Thundersky cells providing 320Ah x 75V (24kWh) weighing in around 600 pounds. If you've got the money, 200Ah lithium cells are available which makes it easy to build exactly 400Ah of 75V (30kWh) from 48 cells. Your pack weight would still be under 800 pounds.
So the first version of your boat could be powered with the 24 T-105s at a cost of less than $4000 for batteries. You would be up and running and be able to collect initial performance data. You could then run those batteries to the ground or pull them while still very new and recover a good portion of the original investment. Then you could upgrade to the 48 200Ah lithium cells for something around $13-14k including BMS. Your boat would lose 700 pounds and your basic range would increase almost 50%. Or you could skip the first step and jump right to the high end batteries (that's basically what I did).
That is one of the advantages to an electric conversion. You can always upgrade later. You might find that the FLA "test" pack is sufficient for your purposes and the upgrade can be delayed indefinately. You could then put the extra $10k towards new sails, winches, solar panels, etc.
You've got a lot of options. And most of them turn out pretty good.
Fair winds,
Eric
Marina del Rey, CA
--- In electricboats@yahoogroups.com, Ben Okopnik <ben@...> wrote:
>
> Hi, Eric -
>
> > ... Flooded Lead Acid (FLA) cells are the cheapest, LiFePO4 (one type of lithium-ion) are more expensive, but more store more power for the size and weight, and AGM fall somewhere in between for cost and performance. 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)...
>
> So for 400AH, which is what they're suggesting, I'm looking at 80 T-105s
> (x 4 for the 400AH, x 12 for the string voltage, and / 0.6 for the above
> figures)? That seems like a rather large battery farm. Time to start
> looking at forklift batteries, maybe?
>
> > Of course, you may be able to find cheaper batteries and I know you can find more expensive ones, but these examples seem to be available to people in most parts of the US. But you can see the math that I did and can work up your own comparison after your shop around.
>
> Eric, I really appreciate the overview; as I said, this is exactly the
> kind of info I was looking for, since it allows me to start boxing in
> the possibilities. Thanks again!
>
>
> Ben
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