zogthegreat said:
I am a newbie to the forum and I have been reading up on the technology, both on this site and on others. I keep noticing people mentioning the fire hazards that Lithium polymer batteries pose.
How dangerous are Lipo's and how paranoid should I be with them?
thanks
zog
Well they're both really cool, and somewhat terrifying at times.
First part of the terror is shared with most of these massive homemade batteries.. you have high DC voltage, high amp capability, and alot of wires that are probably all the same color... so if anything goes together wrong.. doesnt matter if its an errant strand of copper wire, or wrong connectors or RIGHT connectors but not precharged... theres a very real possiblity of metal vaporizing in a blindingly white light.. no literally it can blind you. molten metal can pop.. things can go *poof* literally in smoke... all terrifying when it happens to you, especially in your face.
none of that is lipo specific.... any of these homemade packs could do all that.
It can REALLY get confusing with lipo if you're not careful.. for example lets talk about what I was doing the other night.
I have four big blocks of lipo.. each one is made up of four hardcase blocks of lipo in series. not a huge deal, each block only has 2 wires coming out of them, so build the block carefully, and move on, right?
well.. no. because once I have that, I have the balance wires. they all go in each block, but if any one is plugged in wrong, they WILL cause a wire to vaporize.
This is where the terror comes in. even though I plan everything. I label and color code. I do everything I can to foolproof it. but its still a small bit of terror to plug each thing in. especially the first time.
if anything shorts like that to vaporize, it may make the battery unstable.... not now. but later. Probably when I am NOT looking at it.
lets look at the battery.
its a thin aluminum pouch, and if it punctures... it will ignite with the air.
its a thin aluminum pouch, and if its undercharged... it will swell, and puncture and ignite with the air.
its a thin aluminum pouch, and if its overcharged... it will swell, and puncture and ignite with the air.
its a thin aluminum pouch, and if its held in compression so it wont swell, it will build pressure until the seams blow it out like a small bomb, and then it ignites with the air.
It also has a huge electrical potential, so it can short, create enough heat to ignite everything around it.... until its hot enough to melt aluminum... then it burns with the air.
its a thin aluminum pouch, and if its dented, bent or otherwise mangled, it can create internal resistance(heat, then burn), discharge improperly (overcharge on bulk charging,then burn) or go undervoltage(and then charge and burn)
ok, so its burning... but you can put it out right? well.. no. you'll have to let it go wherever it is. water will not kill it. your fire extinguisher will not kill it.. short of enclosing it in a Halon atmosphere, it will keep going. the fire departments water doesnt stop it, it just keeps everything around it cool enough that more stuff doesnt burn.
So all that said... you want to do it, safely. right?
well first, do you need it? if you dont need to go superfast AND superfar AND have space/weight limitations that cant be met by other methods.. sure. but most likely, something else will work for you safer, cheaper, and easier because its intended for consumers.
so you want to do it anyway, but safe as possible?
That means money. lots of money for things you didnt expect or think of...besides the batteries (they CHEAP in comparison.. right?)
Smart charger... because you need to balance them all.
dumb/bulk charger or super expensive charger... because the pack is massive and it would take hours to charge with the smart charger... unless your pack isnt that big.. and if its not big amp hour wise, why are you using lipo?
cell log, or other way of cell monitoring.. this does NOT replace a BMS, its what informs YOU of how well your BMS is doing.
Your BMS... this can be as simple as a plan to manually monitor.. or it can be a true system with a chip checking each cell voltage.
lipo balance connectors.. to connect them all. you need to parallel packs make taps for your cell log or other...etc
lipo balance connector wire... for above
lipo power connectors/wire... to get it all together down to your controllers power input.
multimeter.. a GOOD one.
software to log/monitor/figure out what pack or cell is good, and what sucks.
see all that? it costs money. the FIRST thing most people ask is... what above can I skip? they convince themselves they dont need a bulk charger, the smart one will work. or they dont need to monitor cells with a cell long, they'll balance charge everytime. or they will keep on track of things with no automatic alarms. or they will use their free harbor freight multimeter, and set their bulk supply with that.
they'll push to a full 4.2 charge everytime, instead of leaving headroom.
they'll run the batteries down to 3.0v "because they had to get home".
they'll forget that the controller lowers the battery slowly... or to check the balance... etc.
This is how most people are, and its rare for people to REMAIN otherwise after they get complacent with it.
THIS is the true danger of lipo. yes they can fail randomly, but 99% of the time its a failure of the human part, that allows the lipo to become dangerous in the first place.
people start out with the best intentions.
then they get used to it.
they then get lazy.
then shit happens.
oh, and one other prerequisite to lipo:
do you have a place where you can charge/store, but if your bike caught fire, it wouldnt kill everyone in the house?
