[oudevolvo]

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?

 

[Ohno]

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?

I like your use of the word "just"! But if someone is there at the time to detect a problem then, with good pump, maybe a battery fire could be controlled. Your hose access to the battery would be a good thing then for sure.

You are so right about the fire extinguisher. I had not thought of that as important for a battery fire because, what's the point? But it's all the other flammable stuff that needs to be protected.

 

[electro wrks]

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.

 

[remy_martian]

You can always put the battery box in its own dinghy and tow it.

Use fiber rope for the tow and it self disconnects in a fire 😂

 

[floydr]

Shouldn't a thermistor or a bunch of them warn the operator in time to flood the battery compartment with continuously flowing water thereby cooling The offending cells/ modules before you would have a problem with high heat >100ºC of course you would lose the modules in the battery compartment affected by high heat. This could even be automated if any thermistor goes above such and such temperature the battery box is disconnected from motor and water starts to flow in and flow out though ports which would be opened when pump is activated.
later floyd

 

[Ohno]

Shouldn't a thermistor or a bunch of them warn the operator in time to flood the battery compartment with continuously flowing water thereby cooling The offending cells/ modules before you would have a problem with high heat >100ºC of course you would lose the modules in the battery compartment affected by high heat. This could even be automated if any thermistor goes above such and such temperature the battery box is disconnected from motor and water starts to flow in and flow out though ports which would be opened when pump is activated.
later floyd

I like this. Someone, other than me, needs to sacrifice some batteries to test it.

 

[Ohno]

You can always put the battery box in its own dinghy and tow it.

Use fiber rope for the tow and it self disconnects in a fire 😂

Perfect.

 

[Ohno]

In the case of a boat, I'd cut a square hole in the bottom of the boat then seal a stainless steel battery box with a plastic bottom to that hole - in the event of a fire, the flaming batteries get delivered to Davey Jones locker.

You know I think your idea might work. It means moving the batteries back 18" and out 12" and so messes with my weight distribution but I can compensate for that. By adding one bulkhead I can create a sealed compartment in each hull. The batteries could sit in a open top box in that compartment and the bottom of that box would be the bottom of the hull that has been cut out. The details of making it watertight and structurally sound are not at all daunting to me. Neither is coming up with some kind of mechanism that lets the box drop.

What I don't know is how the various electrical/electronic components will handle this. Especially the BMS.

I picture it working this way:

• Over temperature alarm sounds.
• Someone, or some kind of automation, 'pulls the pin' and the offending box drops, say to 18" below the hull, and floods with water.
• Now comes the tricky stuff: This boat's batteries are in two packs, one pack in each hull. They are in a 72v 3s2p configuration. Ideally I would be able to disconnect (Anderson connectors?) the submerged battery and plug the battery cables back in to re-energize the controller/motor so we can limp home using the dry pack.
• Is the BMS going to hate this and refuse to allow the remaining dry battery pack to function?
• I'm thinking only the batteries will take a swim, Or maybe a contactor and/or fuses will get wet as well. The BMS wires would get wet too. Everything else would be dry.

Any thoughts?

 

[oudevolvo]

Much easier: not use Tesla modules on a boat and use LFP chemistry instead?

 

[remy_martian]

LFP is double the weight.

You can either "diode-OR" the power connections, which wastes power, or do a power selector switch with contactors to drop the submerged battery from the circuit. Yes, the bms gets complicated - you may need two. Or you could use a pair of manual disconnects. In emergency power, should your inverter care what the BMS thinks? Arguably, you'd want to ignore the bms and toast the pack by overdischarging it if you HAD to get her to land.

In theory, if you used lead bolts for the bus bar connections, or a low melt alloy, it could self disconnect at the drop passively from the heat, maybe suspend the pack by those connections? But - that same system could strand you.

This is also not without risk - you'll make a lot of hydrogen with the electrically live, burning, cells dropping into seawater (explosion risk), though dropping the battery case in might not melt the case but won't cool the cells so it'll keep burning. In rough (anything but glass) seas, the vented case will still flood and sink.

It's a silly thought-exercise, which is ok. Creativity is a muscle that needs exercise.

Your main concern, imo, should be keeping the vessel afloat and sharks starved, not maintaining propulsion, so my vote is jettison a burning pack (this is unlikely to happen, but...can) and maybe do it so the jettisoned battery case "icebergs" to where you can maybe salvage it after the fireworks are done and also not be labeled an eco-terrorist for its sinking by West Coast hippies who hate fossilfuels and also hate hydro dams, wind turbines, solar, and "toxic" lithium batteries - build a pedaled hydrofoil to make the granola munchers happy 😂.

 

[Ohno]

Much easier: not use Tesla modules on a boat and use LFP chemistry instead?

They are heavy and expensive. At least the ones I've found so far are.
The weight of the Li-ion batteries will compromise the performance of the boat substantially compared to an ICE. Batteries that are heavier yet are just not acceptable to me. In a slow boat the LPF would make much more sense.

 

[remy_martian]

A titanium box would be beauty in several respects (including, let it burn) - you seem to be super-resourceful in aerospace scrounging...I suspect an ex-Boeing dude 🤨

 

[Ohno]

LFP is double the weight.

You can either "diode-OR" the power connections, which wastes power, or do a power selector switch with contactors to drop the submerged battery from the circuit. Yes, the bms gets complicated - you may need two. Or you could use a pair of manual disconnects. In emergency power, should your inverter care what the BMS thinks? Arguably, you'd want to ignore the bms and toast the pack by overdischarging it if you HAD to get her to land.

In theory, if you used lead bolts for the bus bar connections, or a low melt alloy, it could self disconnect at the drop passively from the heat, maybe suspend the pack by those connections? But - that same system could strand you.

This is also not without risk - you'll make a lot of hydrogen with the electrically live, burning, cells dropping into seawater (explosion risk), though dropping the battery case in might not melt the case but won't cool the cells so it'll keep burning. In rough (anything but glass) seas, the vented case will still flood and sink.

It's a silly thought-exercise, which is ok. Creativity is a muscle that needs exercise.

Your main concern, imo, should be keeping the vessel afloat and sharks starved, not maintaining propulsion, so my vote is jettison a burning pack (this is unlikely to happen, but...can) and maybe do it so the jettisoned battery case "icebergs" to where you can maybe salvage it after the fireworks are done and also not be labeled an eco-terrorist for its sinking by West Coast hippies who hate fossilfuels and also hate wind turbines, solar, and "toxic" lithium batteries - build a pedaled hydrofoil to make the granola munchers happy 😂.

Not so silly I think. If I didn't want to get back to shore under our own power it seems like it's fairly simple mechanically.

You have touched on what I was thinking would be 'phase two' of my questions: If the battery gets dropped in before it is actually burning would it -

• Catch fire underwater?
• Create an electrocution hazard for someone who reaches into the water?
• Create an environmental problem due to chemical release of some sort?

I was thinking the battery pack would be suspended underwater by stainless steel cables. How far down doesn't really matter much. Though if it is still attached to its over length battery wire I suppose those don't want to be any longer than necessary

What temperature would a battery pack need to reach before it is at the point of no return?

Tesla knows all this stuff but I don't imagine they will tell me.

 

[remy_martian]

It's a chemical fire, doesn't need O2, so it will continue to burn under water until it gets cooled sufficiently.

Anything above 160 (some say 200) degrees is begging for thermal runaway which gets stuff all flamey.

If you're the better, or within a magnitude or two, (guessing) conductor to seawater, yes you could become a conductor. iirc, we're pretty much seawater once dry skin is compromised.

I'd think EPA would frown on lithium battery disposal at sea if it can be foreseeably avoided. Again, guessing. Not good karma to plan for it.

A fire is very unlikely. If you have one, the smoke will be seen by other boaters and you can get a tow. Your primary job should be to protect occupants, which includes keeping the ship from becoming ballast and includes not using ABS, Urethane, PVC, or other toxic plastics near or in the battery box.

Protecting an asset (like half the pack) is nice, but having been in a couple of engine outs in aircraft I was piloting, the last thing in priority is saving the ship, not the first -- saving the ship as a priority is what invites Mr. Death over for tea.

Dropping it into water will hydrolyze seawater into hydrogen and oxygen and it will continue burning since it does not need oxygen to sustain the lithium fire. It will explode because of the hydrolized H2 and O2 plus the burn...maybe a few times. You don't want it anywhere near the boat, or be tethered to it, imo.

Mount it on an angle onto compressed car coil springs, with an aluminum bolt keeping it compressed 🤓

 

[Ohno]

A titanium box would be beauty in several respects (including, let it burn) - you seem to be super-resourceful in aerospace scrounging...I suspect an ex-Boeing dude 🤨

Titanium is great stuff. I never worked at Boeing but 40 years ago my boat shop was just down the street from Boeing Surplus. That was a cool place.

 

[Ohno]

I thought this video was informative. Use water to put out an EV fire. Lots of it.

 

[electro wrks]

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

 

[remy_martian]

If only the guy knew what he was talking about vs a regurge from engineering.

The vehicle does not handle a thermal runaway, it prevents one.

 

[piotrsko]

To repeat another post: my brother the fire truck engineer (pump manager) says there ain't enough water available to put out a lithium battery fire, he just breaks out the coffee thermos and runs enough water to keep the flames contained while he watches it burn. Therefore the reasoning should be: prevent the battery fire in the first place by avoiding the edges of charge and reasonable current limits combined with critical value fuses. Being able to jettison the burning pack is simply silly.

 

[Ohno]

To repeat another post: my brother the fire truck engineer (pump manager) says there ain't enough water available to put out a lithium battery fire, he just breaks out the coffee thermos and runs enough water to keep the flames contained while he watches it burn. Therefore the reasoning should be: prevent the battery fire in the first place by avoiding the edges of charge and reasonable current limits combined with critical value fuses. Being able to jettison the burning pack is simply silly.

Battery fires happen. Standing by drinking a thermos of coffee if a fire starts often isn't a wise option on a boat. Burning, or overheating, batteries that aren't on the boat are less likely to cause the boat to burn to the waterline. Silly or not I think that dropping them into the water is a reasonable course of action. Whether or not that extinguishes the fire is not all that important at that point.