Hi Jason,
You may be interested to know that I've done a somewhat similar conversion on my trimaran, Current Sunshine using thundersky batteries and I have some observations for you.
She is 43 ft overall and weighs around 3 tonne, is an ex-racer so is easily driven. I have a Torqeedo Cruise 4 as main propulsion and a smaller Torqeedo as a backup. The Torqeedo will push her at 6.5 knots full speed.
With the Thunderskies you need to work 3.2v per cell and so to get the nominal 48v I've used 16 cells. This actually gives 53v so you could pull this back to 50v by using 15 of them. 16 cells weigh in at 118kg.
Right now I am running the Torqeedo while attached to the dock to do a full discharge test on the batteries. It seems that to begin with they don't have their full capacity and need to be cycled a few times to achieve the full 200 ah. Today I'll be running them until one cell reaches the low voltage limit of 2.5v. And that will give me a good guide as to the actual ah capacity.
The pack voltage now under load of 1000watts is 51.9 and the voltage of a single cell that I'm monitoring is 3.29v. At this point in the test I've used 50 ah or 25% of capacity.
I have a friend who has installed two Cruise 4's on his 44ft cat and using one Torqeedo he can get about 5.5 knots at full speed and with both motors running it improves the speed only a little to around 6 knots. This cat weighs in at around 6 tonne.
The range improves dramatically with speed reduction. Here are some figures for my boat.
4000 watts 6.5knots 2 hrs
1500 watts 4.5knots 6 hrs
500 watts 3.0knots 16 hrs
I too use an engine only sparingly - after all we do have sailing boats - and I hope to find that recovery of power is easily achieved from solar. I've been in the boatyard for too many months and only now am in a position to prove this after all. Or not :)
Have fun with your project.
Cheers
Chris
On 10/12/2009, at 2:57 AM, jason_d_s_uk wrote:
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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