balancing cells will cause fire easy! what do you think?

[cryzymotor]

Hi guys,

As we know many people use lithium battery or lipo battery without BMS and charging by balancer.
I want to say balancing battery will cause battery fire more easy than no balance.

Im an engineer of electric chemistry technic, and work on making lithium ion cells and packs for more than 10years, now i just make battery packs only with good quality cells.

Why cells are easy fire by balance charging?
First, there must be differece between each cell in a pack, all cells just are most simillar and will not be same never. We just see same capacity and same voltage and same inner insistance, users just can measure this three parameter. But we do not know some defect in production process. In fact there must be some defect plastic saperator with tiny hole packed inside cells, and also there is small thorn on the edge of anode and cathode, these two causes short circuir inside cells. This short circuit will be aggravated more and more serious by charging and discharge, after some cycles we will find some cell different voltage from others, the difference comes from the inside tiny short circuit and resistance change. At this time if the difference is huge, we should stop using battery again, and change a new. If charging the bad cell with balancer, we will not know which is the dead one, and charge and discharge time after time, finally the tiny short circuit becomes real short circuit, so fire must be caused.


So hope you guys do not balance cells again, and BMS is necessary for battery, if your battery works well without BMS, it is just matter of time or you are the lucky one.

What do you think?

 

[amberwolf]

So:

You don't want people to balance cells.

You do want them to use a BMS, which will balance the cells.


What's the difference?


FWIW:

Using a BMS to balance the cells will do so without ever telling you what each cell actually was at; it's all buried in the pack and inaccessible to the user.


Using a balancing charger of the right kind *can* tell the user what each cell was actually at, and/or the user can measure each cell or even individually charge each cell with a charger that counts Wh going into each one, monitors voltage curves, etc., and so it presents the user with the ability to see which (if any) cells are having a problem, and lets them do something about it.

 

[nutnspecial]

Yes, I think the point is that blind balancing can lead to unnoticed dangerous cell degradation, which can lead to thermal runaway on charge or perhaps discharge.

Imo a properly treated pack of healthy cells should very rarely ever Need balance. A small maintence balance doesn't hurt, but might be questionable whether this is even worth it?

When the bms or external balancer needs to always do a heavy balancing, it shows some cells will not be as safe per manufacturer spec or previous use. The chance of error or failure in a bms or balancer also goes up the more they are used.

That's why I think human monitoring in any type of maintenance is the key. That goes for natural balance, internal or external bms/balance charger, battery medic or a lightbulb or single cell charging. Know safe voltages and charge/discharge currents. Know what voltage all those cells are at, regardless if you're relying on their good and matched condition for natural balance or an added means of maintaining balance such as bms or whatever.

Most lithium is volatile enough not to take a chance imo.
Blind bms does make me more nervous than personal monitoring, and we sometimes recommend a user to simply charge a battery for days. Why in the heck do alot of these batteries have no easy way to even see cell/group levels????

 

[amberwolf]

That's why I think human monitoring in any type of maintenance is the key.

Yes, but what the OP is saying is the opposite, where the BMS would do all this, and external balancing should NOT be done.

That's the part that doesn't make sense, because the BMS is the balancer that invisibly fixes the imbalance, letting it get worse and worse without ever letting the user know anything (other than the earlier and earlier LVC point); it doesn't even report when it's done balancing so most users never fully balance their packs, because they see the green light on the charger and assume it's all done and just unplug it, when in fact it might just be off waiting for the BMS to balance a bit so it can put more charge in.

While the external balancer is what allows the user to know what is going on in there and decide what to do either during charging or afterward.


BMS do exist that are like the external balancers, but except for expensive rare stuff like Addapto, they are not on ebike packs, just large EVs. (and the commercially-produced EVs also don't tell the user anything, just store the info in service codes for dealers, so only the DIY EVs would even have something like what the OP wants, if he wants the end-user to know the pack state).


Why in the heck do alot of these batteries have no easy way to even see cell/group levels????

First, because it's expensive to do that. Labor to install the second set of balance wires, parts costs to make them waterproof as external connectors for the encased bike-mountable batteries (rather thah "duct tape" packs),

Second, because almost no user wants to know anything about what's going on in there, they just expect it to work like any other battery in any other device they have, because none of *those* have to be monitored, right? Their laptop or phone batteries just get tossed out when they don't work like they want them to, and they get a new one. They dont' get in there and test it or fix it; that's way too complicated for most people. Heck, even just figuring out that the battery itself is why it doesn't run as long as it used to is too hard for most people.

"What, I have to plug it in and charge it? It doesn't do that by itself?"