Use spinel cells in a battery pack as balancing method

sannder · Feb 9, 2017

I am sure many will advise against it.

Here is the idea - use a couple of series of high power cells 18650, i.e. VTC5/6 in paralel with one or two series of V3 (spinel).
The idea is that the VTC5/6 will do most of the work when high amps are demanded.
At the same time the V3 will help maintaining the pack balanced during charging w/0 using a BMS.

Sure, the discharging curves and the capacity are not identical.
At the same time, I doubt that the flowing currents between V3 and VTC6 will be high enough to compromise the pack .

What do you guys think ?

spinningmagnets · Feb 9, 2017

Have you tried turning it on and off?

Syonyk · Feb 9, 2017

Try it and see. But I think you'd be radically better off with an external balancer. I don't believe the US18650V3s have that strong a self balancing behavior - it's enough when the pack consists entirely of them, and the BionX packs behave well, but I don't know how well they'd handle being in charge of balancing other cells.

In addition, as you note, the balancing currents could be significant. If you do this, put the balancing cells throughout each parallel group, not just at one end.

Cephalotus · Mar 14, 2017

"Self balancing" cells do not exit. It's a myth.

Just make a pack of VTC6 cells, I doubt that you will see any significant disbalancing if you don't mistreat them

Syonyk · Apr 14, 2017

Cephalotus said:
"Self balancing" cells do not exit. It's a myth.

I disagree.

The spinel LiMn chemistry has enough self balancing capability to keep a pack in balance with only bulk charging.

BionX has been doing this for years on their older packs, and after 5+ years and many hundreds of cycles, they're balanced to within 0.01V. I see a lot of those packs, and they behave very well when not deeply discharged.

sannder · Apr 28, 2017

The BionX LiMn 10S6P 9.6Ah pack was still holding 8Ah of charge after 7 years and was running pretty well overall.
Self-balancing seem not to be a problem, however due to age and usage (high amps) the voltage sag was pretty annoying.

I am currently using the "self-balancing" capabilities of LiNiMnCoO2 - and so far so good

Doctorbass · Apr 28, 2017

Cephalotus said:
"Self balancing" cells do not exit. It's a myth.

Just make a pack of VTC6 cells, I doubt that you will see any significant disbalancing if you don't mistreat them

Cephalotus, Please make your search and you will find the light :wink: Sefl balancing effect does exist.

Luke have made great explanation about that:

The charge efficiency of the spinel chemistries decreases slightly as it approaches a high SOC. You can see the effect with a CC supply and a temp sensor as plain as day.
This is what causes them to self balance. (and what causes a lead acid to self balance, only they use electrolysis as the energy outlet)
It is not a designed-in feature, simply an inherent property that helps to self correct balance in packs.
In practice, you can start with a pack that is out of balance, run a number of cycles through it, and each time its finishing the CV mode, you see balance creep a little closer each time until it ends up back in roughly perfect balance after enough cycles. The exceptions of course would be if you have a weak cell, or a very fresh cell with old cells, etc etc.

enjoy!
https://endless-sphere.com/forums/viewtopic.php?f=14&t=27702&p=400595&hilit=self+balancing#p400595

I am building a 20s15p made of 25R and VTC5 to combine with teh adaptto controller bms. The VTC5 will help alot to keep the pack balanced and will make easyer the job for the BMS very small bleeding resistors. As well this is only if i make a bad cell matching job during the cell test before constructions! :wink:

Doc

Doc

Use spinel cells in a battery pack as balancing method

sannder

10 mW

spinningmagnets

Moderator

Syonyk

10 kW

Cephalotus

10 kW

Syonyk

10 kW

sannder

10 mW

Doctorbass

100 GW

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