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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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Yeah, I mean if the metal is thick enough at a certain point of course it will be a non issue. A foot of steel will definitely stop the spread of a battery fire inside (and you can probably ditch the blowoff valve at that point too)! I like the idea @kennybobby mentioned with the nested boxes and a vent, if you really want to be safe. But rest assured that many people have li-ion systems with aluminum siding in the mm-range that have run for ages without issue. Tesla modules also have cell level fusing which is nice in case of a cell failure etc. Everyone's risk tolerance is of course different, so ultimately it's up to you. Li-ion batteries when managed properly are quite safe (see the fire rate of EVs versus ICE vehicles).
In one of Tesla's original patents, it states that their battery fires can burn at 850 C (1562 F). As aluminum melts at ~660 C (~1220 F), it might be a poor choice as a material if you don't want your battery box to potentially burn through and melt in a fire. Stainless steel melts at ~ 2X the temperature of aluminum. It might make a better choice, particularly in a marine environment.
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I wonder if there is an example of a battery box containing a battery fire?
This fire was with Tesla modules. Take heed of the posters message and battery box design:

My car caught fire as well. It was while parked with highest cell at 4,1V.
It is because I used vent valves and a 2mm stainless steel box which kept the fire inside to a large extent so there is at least a car to rebuild
Will share some further details on my rebuild blog later Electric Volvo Amazon wagon from 1967 and converted to 100% electric

I used different ones, but I use these vent valves nowadays Vent valve for battery box - EVcreate
I would say the use of aluminum, plastic, or wood as the primary battery enclosure material with Tesla modules is a real bad idea. That said, As I recall, some Teslas, maybe Ford and Rivian may have Aluminum in the lower portion of their under vehicle battery boxes - but always steel on top, next to the passenger area. Is this to keep a fire down and away from the passenger area, melting through the aluminum bottom first? If you are serious about doing this right, you want to think long and hard about these safety issues.
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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.
This is one of the key safety features in the early battery patent(s) for the Model S and X battery enclosure. Also included in the patent(s) are pressure pop-off valves and a plenum built into or near the enclosure to direct flames and hot gasses down and away from the vehicle.

oudevolvo, could a pop-off or burst valve and vent tube system, of sufficient cross sectional area, directed flames and hot gasses away from your car, and limited the damage from the fire? Do you think the 2mm stainless steel wall thickness box would have generally contained the fire with these features in place?

You mentioned radiant heat damage. Extra shielding or insulation would help prevent this.
In the rare event of a Tesla module fire, people should be prepared for at least a fire like this:

At the time of this fire, people were estimating that this fire only involved 1-3 modules of the 14-16 in the battery enclosure. Apparently, the safety "architecture" built into the enclosure and the quick intervention of the fire dept stopped the fire from spreading.
Here's a video from Munro where the ability of a commercial vehicle to safely handle a battery thermal runaway is discussed @ ~13:10. DIYers should also anticipate this happening with their builds and try to incorporate safety features to handle it, if it occurs

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From the 100.03 regulations( Regulation No. 100-03: Approval of Vehicles with Electric Power Train.) referred to in the video:

"6.12.1. Under vehicle operation including the operation with a failure, the vehicle occupants shall
not be exposed to any hazardous environment caused by emissions from REESS. [Rechargeable Electrical Energy Storage System]"

This is just common sense stuff, people. Why would somebody be so superficial and unimaginative to think the engineer in the video was referring to anything else??!!

As for as relying solely on prevention to deal with battery thermal runaways, let's recall the quote the great popular philosopher, Mike Tyson: Everyone Has a Plan Until They Get Punched in the Mouth

It may be a pain to design, build, and fit a safety system into a boat, car, or aircraft. But, you really, really need to have some way of safely collecting, directing and dumping outside, over the side, out the transom the hot gasses and flames from a battery thermal runaway event. It's just common sense to protect the occupants and the rest of the vehicle.
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I can't believe you quoted a dumbass punching bag on this site 🤦‍♂️
I make it a habit to generally ignore your posts on the forum, let alone quote you.
Ohno, if you are going to use batteries with a potential battery thermal runaway issue, you could incorporate the safety venting system into a rudimentary rocket drive. If aimed out the back of your boat, it could get you safely to shore, if there is a thermal runaway event. It could have a properly sized low pressure blow-out disk on the battery enclosure leading into a classic low pressure rocket nozzle:

You would have to make sure the battery enclosure, blow-off disk, and nozzle are properly sized and made out of the right materials for the heat and pressures involved. This is after all, rocket science.
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