Balancing - Time-Consuming?

[boom]

I don't own an e-vehicle yet.
I've heard that balancing a large pack can take all night.
True?
- Thx

 

[neptronix]

Yes, if hugely out of balance ( rare, except if you have a weak cell, or the pack is crap to begin with - cells not matched and constantly fall out of balance )

 

[boom]

Is it time-consuming to balance a powerwall?

 

[amberwolf]

Buy an EV with a quality well-matched-cell pack, and it isn't a problem--it won't need balancing.

Buy a cheap EV with a randomly-assembled-cell pack, and it can be a problem from the very beginning, and will get worse as it ages.

Or buy a cheap EV and replace the pack with a quality-well-matched-cell pack like those from places that sell used-EV-modules like GreenTecAuto / etc.

Keep in mind that balancing is only making all cells the same voltage at some point in the SoC curve. It does not fix anything, doens't make a battery pack better (and not doing it doesn't make it worse, though it will perform less well).

It isn't needed if the cells are all matched in properties, because they won't become unbalanced.

Unbalancing only happens when the cells are not matched in properties (or there's some parasitic load from the BMS itself on only some of the cells, and it's left sitting unused for a long time).

Cells can become unmatched even if they start out that way, but if they do start that way they're probably going to stay that way for most of their lifespan, like the EIG cells I use that are nearing a decade and a half old that still remain balanced even though they have lost significant capacity and some current-delivery capability, because they were so well-matched that they have aged the same too.

 

[neptronix]

Yeah, here's the opposite case:
You get ( or build ) a pack with super well matched cells and it doesn't come with a crappy BMS that drains all it's power from cell #1, eventually wearing it out.

That pack won't need balancing for hundreds of cycles if ever.

 

[harrisonpatm]

Is it time-consuming to balance a powerwall?

Balancing, at its simplest, is a type of charging. Therefore, time required to balance is dependent on charge current versus battery capacity, as well as the difference between the highest and lowest cell voltages.

So, do you have a massive 100kwh powerwall, and you're trying to balance cells that are 3.3-4.0v, with a 1-amp charger? That'll take weeks.

As you'll see from other advice on the forum, for batteries in general, best practice is to assemble packs that are already balanced, and use cells that are healthy and matched. If you do that, you won't need to balance much at all.

 

[Diggs]

Second Life Storage is a great forum to get these types of answers. Quite a few there run powerwalls and have quite the in-depth knowledge.

 

[dominik h]

You can use an external active balancer, when you have bigger differences in the cell groups.

 

[Matt Gruber]

on an old tool pack, it had a p pair of weak cells, so I added a buddy cell from another parts pack. lasted another year or so on my scooter. so if a cell runs down first, it is telling you it needs a helper.