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Tesla modules in boat

3285 Views 80 Replies 10 Participants Last post by  remy_martian
I am converting a 25 hp gas outboard motor to an 18kW electric PMAC motor for use in a hydrofoil assisted power catamaran. Converting an outboard to electric is something I've done a couple of times but this time I'd like to make my battery safer. My last electric boat is a little lacking in the safety department - Electric Foiling Catamaran from Recycled Parts.

This time I'd like to use 6 Tesla Gen2 XS modules. 3 modules will go in a box on each side of the boat. This is a 72v system so I'm thinking that the 3 modules in each box will be wired in series then the two boxes combined parallel.

What I'm hoping you very knowledgable people here can help me with is battery box design. My thought is to make a watertight (within the limits of the IP67 rated vents) steel box out of .050" - .080" thick sheet that fits fairly close to the size of the 3 modules. That steel box would have a battery box vent Vent valve for battery box - EVcreate
and a layer of furnace insulation on the outside. The steel boxes would be mounted inside of composite boxes that are used as seats and will also hold BMS, contactors, fuses, emergency shutoffs, etc.

This is a carbon/honeycomb boat and I'm fighting to keep the weight down so that I can drag around those heavy batteries without too much performance loss. It kills me to think of 100 lbs of steel boxes onboard but I'm not seeing a way to mitigate the fire risk without something like that. It sounds like aluminum's melting temperature is not up to the job.

Any thoughts? Am I overthinking this? I'm not pulling a lot of current, maybe 200 amps continuous. I think that's like .5C. Charging C rate would be substantially lower.
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Still need to do a writeup on my root cause analysis on my fire.
Regarding battery boxes: the fact that I used 2mm stainless steel battery boxes with vent valves are probably why there is a car to rebuild.
It contained the fire of three Tesla modules until there was nothing to burn inside anymore.
And the front tires still held air.
Thought on the root cause I’ll share on my rebuild blog Electric Volvo Amazon wagon from 1967 and converted to 100% electric but still want to test some hypothesis.
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Have you shared anywhere photos of your battery box?
Thanks, yes, in this blogpost

And when I stopped blogging updates can be found on Instagram @oudevolvo eg around
And on Facebook OldVolvo
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Can you think of any way that you would change your battery box design to better contain a fire?
In the first place my fire mitigating action will be not to use Tesla batteries anymore.
Nowadays there are safer batteries that will give me the right volume, weight and kWh at 96s.
There are two things that could have been better on the box I made:
1) Smarter vent valve positions (so the exits would be where even less damage would occur).
2) A hose connection (not sure how to seal/close that when not in use) onto the box that the firemen could have used to put water inside the box to even better cool at the exact right place
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What did you use for vent valves?
I used vent valves taken from a Tesla Model S battery pack.
Visible on the left and right front sides here
And a separate breather valve also taken from a Model S pack.

Nowadays I use these Vent valve for battery box - EVcreate
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Do you think in your case the vents directed heat at combustable parts near the battery box? Or could the heat radiating from the box have ignited nearby combustibles?
Thanks for your kind words. I think the flames coming from the vents ignited surrounding stuff. Higher up there was mostly radiation and there the damage is not that bad although it has burned there and also underneath the dash.
See also Regarding the hose connection, in my view it can add value in two stages:
1) At the very beginning of a fire where you might be able to cool it down to stop thermal runaway
2) At the end of a fire to ensure it does not light up again
Then just a metal (quick connect) cap can do the trick.
At the hottest point during the fire I'd not suggest to use/open it.
In my box, three Tesla modules burned until there was nothing to burn anymore.
When the heat was more or less gone, the firefighters tried to open it, but I suggested to cut off the MSD instead so that was the way to extra cool down instead of the hose connection. See photo 2 here
But in your case (if you still want Tesla modules on a boat) I'd say try to ensure each module is contained so in worst case it can burn without igniting others.
Think the issue in a Tesla (and others) and the main reason for submersing cars is that you never know if the surrounding batteries got just too hot or not.
In my case I was quite sure the front would not re-ignite since there was simply nothing left to burn.
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Do you think that overcharging was a factor in your fire?
Not likely. The car was not plugged in and the cell with the highest voltage was at 4,05V the evening before the fire.
Will share further details in a blogpost later.
True, but in a car it is quite difficult to keep the flames away from anything that can catch fire at these temperatures. It's just too tight.
And I have a lot of secondary damage. Powder from an powder extinguisher someone who wanted to help used got all the way in the cabin (so I need to replace all wiring).
So ensure you have a proper fire extinguisher to put surroundings out.
But since you are on a boat, can't you just cool and suppress a thermal runaway?
Much easier: not use Tesla modules on a boat and use LFP chemistry instead?
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