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When my brother was building his dream boat he just went with lead acid because of the fire risk. In his boat at least weight and space were not overly critical.Quote:
Originally Posted by BradC
Boat fires obviously have additional risks over land base applications.
Absolutely. I don't want to have to throw my family over the side if a cheap-arse (but expensive and purportedly reliable "Hello SSB read the thread?") lithium battery goes up. The idea of having them in battery boxes in the cockpit is there's no place for the gas to accumulate so they might burn a bit but not explode.
I've read numerous accident investigations on lifepo4 batteries and most of them are related to the battery being in a place where gas could accumulate. The worst was a UK "narrow-boat" where the gas made its way into the cabin through an improperly sealed penetration and built up to an explosive proportion (which is between **** all and a lot for hydrogen) and the thermostat on the fridge sparked it off.
Lead acids off-gas a stoichiometric mixture of oxygen and hydrogen. I've had to help on a mates boat where a lead-acid "let go" with a massive ****ing bang. The difference is it's a one off "spew acid everywhere", rather than a "let's keep emitting fuel until we've sunk". Still had holes all over my clothes and had to slush the engine room out with a bicarb/water mix, but didn't kill his family.
Once the firies had put it out and the Oka was flooded with water and retardent the bloke in charge asked what other batteries of any type were on board.
I said various torches with rechargeable batteries, laptop, kindle, tablet etc etc, two Dewalt 18v wet cell auxilary battery in a cradle underneath on LHS just the same as the RHS and a 400ah lithium house battery. He nearly had a hearty at the last one especially as i said it's directly above that battery that's caused the fire.with only a 19mm pywood floor between them.
The order was then to please remove all batteries from the vehicle before they left.
Which we did plus i educated the firies to the fact that Winston LYP cells that the house battery was constructed out of were in no way flammable and in fact two of the eight cells that made up the battery had been burnt and heated externally by the fire but were still fully charged and the pack was still sitting at 13.3 volts.
I've since replaced those two burnt cells and obtained two secondhand cells to replace them and the pack is still functioning as it has for the last 15 years.
The Australian supplier of Winston cells also asked me when i told him what had happened "why didn't you just get four 100ah winston cells and use them as a starting battery.
With the addition of a small cell balancer we've been doing that for over ten years with our fleet vehicles!!"
Which i may well do the next time one of our vehicles requires a new cranking battery.
following in on this...
recently I got to have a look at a "lithium starting battery" which had had a bit of a calamity..
inside whats left of the box is a pack of smoke damaged lithium pouches, a BMS and a 10pack of very not small capacitors or more accurately what was left of a 10 pack of of not very small capacitors The internal burny melty carnage is all confinded to the area with the capacitors
Best guess (and I support the theory of both construction and fire cause) is the capacitors deal with the sudden ask of amps like a capacitor jump starter but for some reason this one had a capacitor or 2 die and short out taking the brunt of what the pouches could deliver turning it into heat then catching fire..
Pondering battery safety. I wonder if battery manufacturers (or installers) have considered fitting in something akin to the old fire grenades, the element fire extinquisher sticks or the cheapy 2 pack thermal rupture disk puck extinguishers you can get off ebay/amazon.
Side thought,, a soda stream CO2 cannister with a rupture disc inside the battery would purge the 02 out and with a rapid venting of compressed gass, cool the battery itself internally, at least, a little.
Interesting idea. I thought the reason why these fires were so hard to put out though.. was that they generate their own hydrogen and oxygen. So adding CO2 might not be as helpful as you'd hope.Quote:
Originally Posted by Blknight.aus
I was of the understanding that it was a combination of the heat (from the cell shorting) and the hydrogen and o2 so you have all 3 sides of the fire triangle for the older lithium ion batteries but no so with the lifepo4s as they dont have the o2 element attached.Quote:
Originally Posted by Captain_Rightfoot
In anycase if anyone wants to get all mad scientist and has one of the larger Li-ion batteries and wants to play silly games for some potentially silly prizes, Im happy to grab the co2 cans...
with my luck we wouldnt get the damn thing to light.
It is my understanding also. They will undergo thermal runway and pump out hydrogen. The issue as I understand it is lithium cobalt cells emit fuel and oxidiser and then sets fire to it. That’s almost impossible to extinguish and makes a mess. Lithium Iron Phosphate will only emit hydrogen. That has a hugely wide lower and upper explosive threshold, so the hydrogen builds up until something sparks it and all hell breaks loose.Quote:
Originally Posted by Blknight.aus
Lifepo4 batteries can outgas hydrogen if the cells are physically damaged. i recall CATL did many tests years ago where they shot holes in the cells without fire , just smouldering and swelling. in a restricted area the hydrogen could explode of course. They can be cooled with water.
Regards PhilipA
tests of lifepo4 cells with penetration testing - Google Search
My understanding is with LIFPO4 you have to have a lot of bad luck to get them to go. And even then they will try and go out!
Re this thread it is as ever complex. What type of cells do they use? What if the Cap goes up instead. It's all messy.
Magnesium will burn in CO2. School science teacher put burning Magnesium ribbon into a flask of CO2 and it pulled the O2 out of the gas, leaving black spots of Carbon spattered on the glass.
TAS Fire Service keeps bags of dry sand in a warm area for metal fires, Magnesium can do similar with H2O but rather than little spatters of Carbon, it releases the Hydrogen which if ignited has a strong affinity for O2 in the air and can be quite explosive.
Cheers