Safer battery pack construction.

[EUCMania]

Occasionally, we hear someones' li-battery packs catch fire. One reason is that as battery cells aging, some cells develop internal shorts. Once such short is established, that cell is quickly drained, and even worse it has almost no electric resistance so that the cells parallel to it will dump huge current through this cell. the heat is high enough to burn this cell and trigger thermal runaway on neighboring cells. Then fire starts which is hard to put off.

One way to prevent this chain reaction is to use fuse wire for parallel connections. Look at Tesla's battery construction. See first pic

Another way is to build fuse wire into the nickel plate connecting batteries. See 2nd pic. The thin part will melt like a fuse if the current through one cell is too high.

I would like EUC manufacturers adapt fuse wire design in their battery packs. They can brag about this safety feature if they use this technology. @Jason McNeil, can you suggest this to EUC makers?

See https://www.electricbike.com/introduction-battery-design-2/

[Chriull]

2 hours ago, EUCMania said:

Occasionally, we hear someones' li-battery packs catch fire. One reason is that as battery cells aging, some cells develop internal shorts. Once such short is established, that cell is quickly drained, and even worse it has almost no electric resistance so that the cells parallel to it will dump huge current through this cell. the heat is high enough to burn this cell and trigger thermal runaway on neighboring cells. Then fire starts which is hard to put off.

A cell with internal shorts does not short neighbouring cells. The chain reaction is triggered solely by the heat of the first bad cell which causes the neighbouring cells to start burning, too.

As far is i got this last burning EUC incident (if it's the same as you mentioned. ?Was a 9bot E+?) it happened while charging - enough bad cells which cannot get charged anymore so the rising voltage from the remaining good cells does not stop the charger(1). So one of the bad cells with internal shorts heats up to much (thermal runaway) and by the heat all others start burning, too.

Something that can happen to (almost) every wheel now on the market once the battery packs get old enough...

Ninebot took a right path with new "more intelligent" BMS "supervising" single cells. Unfortunately they drain the battery packs too much by this...

Quote

One way to prevent this chain reaction is to use fuse wire for parallel connections. Look at Tesla's battery construction. See first pic

Sorry - only got this now with the paralleled cells!

I always "imagined" paralleled cells age together - its not one that "dies" imediately and shorten the other one. Maybe this is just what happens most of rhe times? Since this fuse wires are usedin commercial mass products, this has to be a risk factor!

But as a base better BMS are needed as "basis" to eliminate the imo higher risks involved with i.e. charging aged packs. Maybe this risk is automatically eliminated by us users - that we replace the aged packs early enough in because of the perfomance loss in such cases?

But anyhow - would be another great step if wheel manufacturers would peak at the actual used safety mechanisms for e-cars and take over at least some of them!

2 hours ago, EUCMania said:

See https://www.electricbike.com/introduction-battery-design-2/

Seems like a highly interesting article! ... but too long to read it now - so marked for to be read soon. Looking forward too learn something new!

 

Edit:(1) quite some bs😁 - charging is stopped once one cell reaches the 4.2xV threshold... But maybe some mixture from mechanicaly misused cells from the E+ casing, bad cells, balancing getting good cells below the threshold again, ...

PS.: Such a fuse wire should be a safe and easy security measure (if they find an appropriate manufacturer), as better BMSs. Just designing something new, testing and setting up the production could get costly... Especially if the first charges are shipped with faults...