External balancing chargers in place of internal BMS

[Fallingwater]

Given my proclivity to experiment with battery packs of various configurations on my e-scooters (and just wait till I get into e-bikes...) I'm wondering if it makes sense not to bother with internal BMS installs.

I've been into FPV quadcopters for a while now, and have a bank of four ISDT SC-608 balancing chargers each capable of 6S and 8A. I could wire my scooter batteries as multiple series of 6 with suitable balancing plugs; to charge I'd disconnect the sections, plug each into a separate charger, charge them up, then reconnect it all up and use the scooter. It'd be mildly annoying to have to fiddle with the plugs, but the advantages would be significant - aside from simple balancing I'd be able to check each cell for capacity and health. I could also charge at 8A, which is a significant step-up from the 2A or 3A that most scooter chargers do.

My one doubt, and the reason I'm writing this post, is that such a system would only check battery balance and health upon charging; the battery would be left to its own devices while being used inside the scooter, with only a fuse in series to protect it in case of shorts. Undervoltage wouldn't be a problem as my scooters' controllers have built-in protection for that, but I'm worried about in-use imbalances.

This doesn't seem to be an issue for my drones; I fly them, recharge the batteries, and notice while recharging if one of the cells has something weird going on and if I should take action. However, I'm being told in various scooter groups that not having constant balancing while in use in a scooter is a problem.

Is it?

 

[john61ct]

For me, this is the best way to go for packs not easily broken down and reassembled, especially those built from soldering or spot-welding techniques.

Constant balancing being required would indicate battery packs that should have been retired long ago.

Those taking a hard line "must always use a BMS" are usually low-information users or those who cater to them.

The term "a BMS" is just a collection of protective functionalities, how you skin the cat up to you

BMSs are often cheap and thus prone to failure, often early-murdering packs they are designed to protect

It should be easy to remove / replace them for testing, replacement and upgrade purposes.

And balancing gear is available that is much better than what is included in most BMS, often marketed as "non-protective" BMS.

Many users are "human BMS" just monitoring voltage and reducing/stopping discharge as SoC goes low.

Many quality chargers terminate based on per-cell voltage, a simple pack-level HVC may even be enough for redundant protection,

OCP and shorting protection can be fuses, even fusible links as Tesla does.

Temperature protection is often independentof the usual BMS functionality.

Each of these functions can be implemented with hardware to protect many different packs, potentially saving money compared to hard-wired BMS.

But designing your own system to work better than just using "a BMS" is not easy, does take more knowledge, and rarely is actually cheaper.