just bring a extinguisher ball with u all the time, if battery goes boom boom, then u can throw the ball in the fire
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What kind of fuse would you use for discharge lead? Double your batt max?
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I wouldn’t use a fuse for that, or at least make it double the amperage you’ll ever be drawing.
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Yeah I figured. It seems potentially risky. Last thing you want to do is lose power mid ride.
I was more thinking, what physical type of fuse fits the bill for this?
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Battery fire is actually extremely difficult to put out. I wouldn’t count on extinguisher ball to help much. You really want to avoid battery fire at all cost cuz it’s no fun:
In case it does happen your best bet is to move the board somewhere it can burn down in a controlled way without putting anything else on fire.
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A discharge BMS or a fuse is a must in my opinion. I try to use both if possible. Fuse rating depends on the speed. If you use a slow fuse i wouldn’t go much over your max Current or it just wont do anything. Im pretty sure 2 times max battery amps wouldn’t help you at all.
charge BMS / Balancer is even more important to prevent fire. Recently a board of a friend almost burned his flat down because he wasn’t using a charge BMS.
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i know battery fire is serious shit, it was just meant to be a jokey reply about the extinguisher ball thing 
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From my experience if a short on esc happens with a bypassed bms the huge current from the battery usually just blows up some component and thats it.
And if a battery is shorted, it usually just sparks as its a small short and eventually a p group dies and you notiece it, unless the builder really fucked it up and serious shorts happened to ignite the cells, which is quite hard when you have even the slightest amount of insulation between p groups. And a discharge bms doesnt help here as it cant do anything
So the best bet to deal with battery fire is to build your battery properly and do a slight amount of cable menagment
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That poor Davega…you can hear it crying “Someone! Please save me! HELP!”
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This. The extinguisher isn’t for the battery, its for everything around it. Once the lithium ignites its not going to go out until its done, no matter what you do.
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Did you ever track down the specific cause of the overtemp cell that led to fire?
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Unfortunately not. It’s a mystery. The only hint I have is that the Unity connector desoldered itself.
So probably something shorted out around there.
Now that I think about it, it would have been worthwhile checking the continuity between the two desoldered lead.
Here’s how everything looked inside the enclosure before the accident.
I had an XT90 parallel adapter for connecting an external battery.
Maybe something went wrong around the parallel adapter. It’s really strange though. I have done all the soldering myself and I believe my soldering skills are pretty decent.
Also, I have used this for a few hundred km both with and without the external battery before the accident happened.
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MMMMMMmmmm Well, in case of fire…
Run to the hills…Run for your life…
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hmm, what if you integrated dry gunpowder into the deck and when it catches fire, it detaches the battery part from the rest of the deck? 
#buildingforfailure
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That’s an interesting idea. I’d love to see something like an over or under-discharge cutoff sensor built into the voltage meter that most VESC’s have.
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Did you have any kind of padding around the pack? From my perspective it looks like the pack was rubbing against the rough interior of your enclosure. It’s hard to tell without being able to see the battery construction itself but it looks misshapened.
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There was no padding but I don’t think this was the problem. For the rubbing to happen the pack would have to move inside the enclosure which it didn’t because it was taped to the enclosure with a strong double-sided tape. When I occasionally needed to remove the pack from the enclosure for servicing, it always required a lot of force. Also, if there was any rubbing, that would cause damage to the shrink wrap and there wasn’t any.
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I’m late to this party but there’s no metallic lithium in a rechargeable li-ion cell to react with anything. Only non-rechargeable lithium-metal cells have actual lithium metal in them.
You’re right about the extinguisher. The very high temperature exothermic reactions that are running wild in a cell that is in thermal runaway make putting out a battery fire very hard to do. The cathode material supplies oxygen and both the plastic separator sheet and the flammable electrolyte liquid supply fuel for the fire.
The best way to stop a li-ion fire is with water or an aqueous fire-fighting solution. This can quickly lower the temperature of the cell(s) below the thermal runaway threshold, keeping the fire from restarting once you put it out. Then it’s a simple matter of just putting out the fire from the burning plastic and organic solvents with more water or an extinguisher.
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