My e-board caught fire

[Ykick]

Serious fallacy trusting “cells” to always be healthy and assuming a few checks is all it takes to play with this chemistry. Cells (particularly pouch format) can and do change.

Hell, one cell in a 10S string discharging and shorting to 0V can still show 33.8V pack voltage if the other 9 cells are 3.75V. If you’re relying on every cell to be in balance 100% of the time, you’re gonna wind up running something to dangerous OD levels.

You either need an alarm and/or check cells every charge/discharge or a BMS to handle when things get out of whack. Otherwise, you’re just guessing and guessing can and will most likely suffer serious consequences.

Oh and btw, even with a properly monitored/managed pack, 3.4V/cell is asking for trouble. Look at this discharge graph demonstrating how little energy exists below 3.65V:



It’s also just a crap shoot which cell is gonna dive off a cliff before the others…

OP dodged a bullet here and now it's time to learn and improve handling/use.

 

[torqueboards]

I agree... from wasting tons of money on packs... I find 3.7v even 3.8v to be the cut off for LiPo's.

Once I go 3.3v or 3v the cells will degrade so much quicker..

After cutting them off at 3.8v cells and packs last way longer. 3.6v won't hurt once in a while so I think.

 

[bbq870]

No oxygen to feed the fire.

actually not... Lithium burns exothermic. means no oxygen from the air is needed. once they heat up to a certain temp, its NOT reversible.
they would even burn under water. (I assume?)


with the wooden enclosure you are right. it can prevent bigger damage.
Justin at Grin is experimenting with potted cells which are completely cast into resin. they also DO burn, even with no oxygen but there's little to no damage for the outside world.

we need to understand, that Lithium cells are not AA batteries.
I compare them to crossbows or similar.
you need to know how to handle those things,otherwise things can go south BIG TIME.



so you COULD use puffed cells, but would you use a damaged crossbow?
we should not trust these cells. even the new ones. for me that's the only way to handle them.

 

[pcerbu007]

hey, I have a drive kit from diyelectricskateboards.com what size belt do you have on, I have a 5m280, want to go smaller to make motor mount stronger

 

[4LivesPerGallon]

I agree... from wasting tons of money on packs... I find 3.7v even 3.8v to be the cut off for LiPo's.

Once I go 3.3v or 3v the cells will degrade so much quicker..

After cutting them off at 3.8v cells and packs last way longer. 3.6v won't hurt once in a while so I think.

Newbie LiPo question: Don't your cells have individual, built-in, protection circuits that prevent too low voltage, and damage? If not, why?

Also, a question for those who have already spent a small fortune on LiPo packs: What is the "best practice", so we don't have to repeat costly mistakes?

 

[izeman]

I agree... from wasting tons of money on packs... I find 3.7v even 3.8v to be the cut off for LiPo's.
Once I go 3.3v or 3v the cells will degrade so much quicker..
After cutting them off at 3.8v cells and packs last way longer. 3.6v won't hurt once in a while so I think.

Newbie LiPo question: Don't your cells have individual, built-in, protection circuits that prevent too low voltage, and damage? If not, why?
Also, a question for those who have already spent a small fortune on LiPo packs: What is the "best practice", so we don't have to repeat costly mistakes?

have you EVER seen ANY lipo pack that has built-in short protection of built in bms? no.
that's why ppl use BMS to NOT have to worry about over and undercharging the pack. if you got a pack that had a manufacturing issue than you can't prevent something bad to happen. no way. but this will happen with ANY chemistry.
sure a BMS can brake as well and cause harm. but still i don't know of ANY professional equipment that is NOT using any. even the small nicad/nimh/18650 packs for your power drill have them built in for a reason.
a BMS for a skateboard costs next to nothing and makes charging so much easier. not 100% sure that a BMS would have prevented that fire, but chances are good.
also LVC or 3.3v is WAY too low imho. as stated before, there is no energy left in the pack below 3.5v and the pack will go out of balance below 3.7v. so if the pack was abused before, over/undercharged with a too high c-rate, then the internal resistance would raise, and if you draw a lot of amps from such a pack at a very low voltage it will get VERY hot. this could lead to self ignition. of course packs age as well. the older/more used they are the higher the internal resistance will mostly be. so this also has to be taken into consideration.

 

[joop1987]

The BMS for Lipo's are inside the charger. Cheap lipo's are designed for RC planes so to keep the weight down. Sure they can be safer with a BMS and a hard case.

 

[izeman]

The BMS for Lipo's are inside the charger. Cheap lipo's are designed for RC planes so to keep the weight down. Sure they can be safer with a BMS and a hard case.

????. a BMS not only manages charging but DISCHARGING as well. and the charger's BMS won't help during usage of the vehicle.
the skateboard will have no problem with 50g extra weight of a BMS.

 

[joop1987]

The BMS for Lipo's are inside the charger. Cheap lipo's are designed for RC planes so to keep the weight down. Sure they can be safer with a BMS and a hard case.

????. a BMS not only manages charging but DISCHARGING as well. and the charger's BMS won't help during usage of the vehicle.
the skateboard will have no problem with 50g extra weight of a BMS.

Lipo's can output more current than a BMS can regulate. The 6S, 12 Ah lipo I'm using can output 120A. They are not needed unless you use a brick style charger with no balance connector. All ESC's have battery cut off's to prevent over discharging. If you want to control the amount of current, the VESC can do that too. With a BMS, you are not balancing each cell individually if using a battery pack cells are grouped in parallel.

 

[s28400]

Yep, that is why I stay as far away from lipos as possible. I will gladly shell out the $$ for a123 26650s or other safer lithium cells over lipos.

 

[eva-michael]

Use LiPO very carefully. battery pack should build under very good protection to avoid physical damage（cause tab or cell internal short circuit）. Also cold solder of tab is a one of the important reason of LiPO fire accident. All these are "critical".
High C rate discharge of LiPO will make me feel like heart attack. Because heat from High C discharge are rising temperature and you just don't know how high now. Melt, short circuit of LiPO is critically dangerous.

That's just why Tesla spend a lot to develop their battery management system with cell monitor, cooling, ect. Tesla's cre is their battery management system. Not cells.

When I communicated with many ebike suppliers in Europe, actually most of them will worry about risk of fire from lipo. Especially those who sell a lot of electric bicycles. All their bikes with lipo are 1-1.5C discharge.

LiPO is cheaper for purchase. LiFePO4 is with much safer chemistry feature and double to triple true cycle life.

BTW, check the data of cells before purchase, many lipo and some low quality lifepo4 are not developed for electric vehicle as they don't suit the application feature of electric bike and cars.

 

[eva-michael]

The BMS for Lipo's are inside the charger. Cheap lipo's are designed for RC planes so to keep the weight down. Sure they can be safer with a BMS and a hard case.

????. a BMS not only manages charging but DISCHARGING as well. and the charger's BMS won't help during usage of the vehicle.
the skateboard will have no problem with 50g extra weight of a BMS.

With a BMS, when current over load or short circuit, BMS will cut off or damage mosfet in side the BMS in some situation . If no BMS, damage cells.

 

[izeman]

The BMS for Lipo's are inside the charger. Cheap lipo's are designed for RC planes so to keep the weight down. Sure they can be safer with a BMS and a hard case.

????. a BMS not only manages charging but DISCHARGING as well. and the charger's BMS won't help during usage of the vehicle.
the skateboard will have no problem with 50g extra weight of a BMS.

Lipo's can output more current than a BMS can regulate. The 6S, 12 Ah lipo I'm using can output 120A. They are not needed unless you use a brick style charger with no balance connector. All ESC's have battery cut off's to prevent over discharging. If you want to control the amount of current, the VESC can do that too. With a BMS, you are not balancing each cell individually if using a battery pack cells are grouped in parallel.

my argument was not to limit max current from the battery to the controller. this is done by the controller itself of course. my argument was, that a BMS looks at every cell (be it in parallel with others or not) and shuts off if ONE cell goes below a set treshold. if you only look at the pack's voltage as SOC indicator and you have a bad pack than you've already lost. it's that simple. but that's just common sense, if you want to make lipo safer. if you don't want to take this extra caution it's up to you. it probably would have helped the thread starter.

 

[Ianhill]

I melted 3 10s9p 18650 packs by not monitoring individual cell voltage rather i depended on the lvc and it works fine if the packs remain balanced and in good health but soon as one cell drops out you need to know. so I use a shunt and voltage gauge now so I can workout my watthour on the fly and see the pack as a whole and then 1-6s lv buzzers on each pack for my meltdown warning.

 

[Paragon]

I melted 3 10s9p 18650 packs by not monitoring individual cell voltage rather i depended on the lvc and it works fine if the packs remain balanced and in good health but soon as one cell drops out you need to know. so I use a shunt and voltage gauge now so I can workout my watthour on the fly and see the pack as a whole and then 1-6s lv buzzers on each pack for my meltdown warning.

Was that with a BMS?