Seller said, not use BMS with mix brand or old battery!

[General_Lee]

Hi guys, I will build my first 48v pack with recycled 18650 battery. (13s 8p) I would like put a BMS like here:

http://www.ebay.ca/itm/48V-54-6V-13S-45A-Lithium-ion-Li-ion-Li-Po-LiPo-Polymer-Battery-BMS-PCB-System-/221740200277?hash=item33a0bef155:g:dywAAOxy1klRa8a0

But this seller not recommend to use it with old batteries and with different brands. What do you think?

Thanks

 

[Syonyk]

Old or recycled batteries tend to have capacity that's all over the place. Which means that the BMS for them may have to bleed a lot more current to balance them.

A pack built of brand new 18650s straight from a reputable manufacturer will have very little difference in capacity between cells, and they'll all age together - so the BMS balancing is fairly easy, and doesn't involve much current flow.

Your pack of junk cells, even if it starts with similar capacity parallel groups, will drift radically more over time (some cells may be 2 years old, some may be 5, etc). This is much harder for the BMS to deal with, and may lead to overheating of components that are not designed for that type of use.

Will it "work"? Sure. Will it hold up long term and do what you expect? Maybe. The seller clearly thinks it isn't designed for that use case, though.

 

[999zip999]

He's saying that is best to use new matched cells. All you can do is play be careful as no guarantee

 

[teklektik]

It's quite likely an issue of the balance current spec.

The linked eBay BMS balances with only 60ma. Cell banks that are unmatched are going to take a while to bleed away excess charge to balance.
Compare to this BMS with a balance current of 162ma which will get the job done 2 1/2 times faster. With matched cell banks, things won't go far out of balance each charge and may just require a bit of tidying up. Mismatched cell banks are going to require balancing every charge - sometimes quite a bit - so heftier balance capability should be in order.

BMSes aren't an area of expertise for me, but I think this is the primary consideration. Other characteristics (LVC, overcurrent, etc) are not going to be affected by unmatched cells.

 

[General_Lee]

Thanks guys I understand. 8)

I will build the pack with each parallel bank with the same brands and capacity. But each bank in serie will not the same capacity and brands.

Question

Without BMS, batteries pack fully charged, when I will discharge it, each bank will still stay equal because as it is connected together? or is it possible than some bank drop faster then other?

Same thing when I will charge it?


If I need only to monitor the total voltage pack during discharge, it'll be ok for me. :lol:

 

[Syonyk]

No, I don't think you don't understand, because having different capacities on the different series groups is what requires a high balancing current to equalize out.

Cells connected in parallel behave like one big cell. You want all of these large cells to have, as close as possible, the same capacity, and same internal resistance.

*shrug* It'll probably be fine, just accept that it'll take longer to charge. However, I strongly suggest using a BMS with a per-series-group low voltage cutoff, because doing a pack like this and having a few cells go weak is a great way to drag a series group well below 3v and start doing damage to it. Bulk pack voltage alone does not tell you if an individual group is below it's cutoff voltage. Lots of people have damaged lipo pack builds this way, and damaged lithium batteries are known to catch fire during charging.

 

[teklektik]

What he said ^^^^

You might shop around and see if you can find a BMS with higher balance current.

Another solution might be:
A few members here have had good luck with this D166 BMS - they seem to cost around $50. See: https://endless-sphere.com/forums/viewtopic.php?f=31&t=63259.

Just email them and ask for a quote for qty (1) Li-ion BMS for 13s of such and such a model with standard settings. You can get specific voltages, but it takes longer and the stock settings seemed workable for the models I checked in the past. A short an sweet request helps get a fast response...
Anyhow - an option....

 

[General_Lee]

I mean, I understood the explanation above about BMS and old batteries.



I reading in the FAQ here and If I understand, you can build pack (with recycled) cells but you need to make each parallel groups with the same brands, the capacity and IR cells.
After that, you can put together each parallel groups in series, even if each parallel groups it not necessarily the same brands, capacity. This is right?

 

[titusmc]

The most important thing is that the parallel groups of cells have the same total capacity. Then, assuming they start at equal voltage, they will drain at the same rate when the pack is in use, and the end resting voltages should all be very close. If they are not close, then when charging some groups will hit the 4.2 volt limit before others and the BMS will need to bleed these groups down before resuming the bulk charge. This takes significant time for a low balancing current if the parallel groups are not well-matched and get wildly out of voltage balance.

 

[General_Lee]

The most important thing is that the parallel groups of cells have the same total capacity. Then, assuming they start at equal voltage, they will drain at the same rate when the pack is in use, and the end resting voltages should all be very close. If they are not close, then when charging some groups will hit the 4.2 volt limit before others and the BMS will need to bleed these groups down before resuming the bulk charge. This takes significant time for a low balancing current if the parallel groups are not well-matched and get wildly out of voltage balance.

Ok good! I will check for the BMS you suggest here:
Another solution might be: A few members here have had good luck with this D166 BMS - they seem to cost around $50. See: viewtopic.php?f=31&t=63259.

 

[Syonyk]

I reading in the FAQ here and If I understand, you can build pack (with recycled) cells but you need to make each parallel groups with the same brands, the capacity and IR cells.
After that, you can put together each parallel groups in series, even if each parallel groups it not necessarily the same brands, capacity. This is right?

Don't assemble a battery of parallel groups with wildly different capacities. It's going to be, at best, difficult to keep balanced, and at worst, unsafe.

Why are you so dead set on building a pack with junk cells anyway? It takes a huge amount of time for what often end up as simply bad battery packs. Most junk cells are not suited to electric bike use (very low C-rate cells with a high IR).

 

[General_Lee]

I reading in the FAQ here and If I understand, you can build pack (with recycled) cells but you need to make each parallel groups with the same brands, the capacity and IR cells.
After that, you can put together each parallel groups in series, even if each parallel groups it not necessarily the same brands, capacity. This is right?

Don't assemble a battery of parallel groups with wildly different capacities. It's going to be, at best, difficult to keep balanced, and at worst, unsafe.

Why are you so dead set on building a pack with junk cells anyway? It takes a huge amount of time for what often end up as simply bad battery packs. Most junk cells are not suited to electric bike use (very low C-rate cells with a high IR).

I know about parallel groups, I explain above. Maybe my English fail

The old batteries cost nothing and I take my time to test each cells in the tools pack. Each cells who passed the test, I put them in the side. When I can build the pack, I make it. I know, is not the best, but if I can have a pack for low price to put in the old E-scooter exemple, is good for me. This is for my fun. Often a old pack can run some time.

For me personally, I use only a new batteries with my E-bike ot E-Scooter.