Jason,
To my eye, your estimates are off. I've got a few questions and comments.
Thundersky LiFePO4 batteries should be calculated at 3.1v - 3.2v nominal. Typically, they are linked serially in groups of 4 to replace a 12v lead acid battery. Which leads to "why 13"? 12 cells will drive a 36v system, I've purchased 16 cells for my 48v system. 16 200ah cells would have a total rated capacity of 10Kwh (200ah x 50v) or 8Kwh usable.
What kind of catamaran do you own? 1500w @ 5kts is an extremely low estimate for any 30' boat. I would only believe it with a ultra-lightweight beachcat type of racing boat and probably not then. For a heavier cruising cat with a bridgedeck cabin, 3kw @ 5kts may be difficult to attain, especially using converted outboard drive legs due to efficiency losses in the gearing.
Although more expensive, Torqeedo Cruise 4.0 motors seem to be the most efficient outboard replacements readily available today. They are also extremely light at only 18kg per unit. With a maximum draw of 8kw, a pair of these should have enough power to overcome windage while docking. Even with these motors, 3kw will still probably not deliver 5kts.
I only bring these numbers up to make sure that you don't invest a lot of money and end up with a system that doesn't fulfill your requirements.
Fair winds,
Eric
Marina del Rey, CA
--- In electricboats@
>
> Hi, i've been watching this group as I'm hoping to do a conversion in the future on my 30ft cat.
>
> I'm realistically upbeat that this can be done and have the following as my concept.
>
> 13*200ah Thundersky Lithium Batteries
> 94.9 KG, 9.75 KW ( 200ah * 3.75v)
> 2 motors attached to twin outboards as replacement for the engines.
> 2 Controllers, BMS etc.
>
> Based on a previous post, using 1.5kw /h @ 5Kts, this would give me:
> 9.75/1.5 = 6.5 hours continous use. Limit it to 80% DOD = 5 1/4 hours.
>
> As reserve, I would have a small generator (honda 2kw) which is about 25kg and a couple of gallons fuel. This would provide me with at least 12 hours running in an emergency situation.
>
> This also excludes the 1 x 200W solar panel and 400w Wind Generator which main use would be recharging for free.
> My requirements at the moment are for sailing a couple of days, then stopping at a harbour overnight. Having done this recently, the most time I used the engine for was 2.5 hours in a day and more likely 1.5h which would easily be recouperated by the wind/solar gen.
>
> The two motors this setup would replace would match weight wise (50kg x 2).
>
> Any comments?
>
> Regards, Jason.
>
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