No such thing as Self-Balancing 18650V (Makita)

[fizzit]

Make any pack self-balancing! Just put an equal resistor across the tabs of each cell. Due to ohm's law, the cells with higher voltage will discharge faster, and the whole thing will act like a voltage divider. Just make sure not to let it sit for too long

[liveforphysics]

I have heard so much about the incredible self-balancing property of 18650v (apparently used in Makita packs) . Does anyone know where I can get a manufacturer's data sheet that describes that property? Thanks.

Sam

Edit: Original thread title changed: "Data sheet for SELF-BALANCING 18650V"

You should remane your thread again...

In the industry these cells generally are NOT used with any balancer.. BionX and Makita are some of them

Few month ago Makita began to install cell monitoring on their pack to try increasing the life and refuce the deffecitve pack. Thanks John in Cr for mentioning that. I also got few of these new gen packs but from now had no time to test them as hard as i tested the most known gen.

Plus the experience of over 200-300 users of these makita on the E-S that dont use balancing feature is a valuable data.

The real history about " self balancing".. came from the fact that these big known manufactur DONT use balancer in their batteri desing.

What LFP said make sense to me.

no real need to search further...

Our pre-release Nissan LEAF sample pack at work had no balancing capability in its pack because its a spinel chemistry. It can only monitor to watch for a cell failure/weak cell, but it uses the cells themself to stay in balance, and they do, perfectly.

[John in CR]

LFP,

Thanks for the explanation. Balancing a little bit each cycle on the way up makes perfect sense. How do you think charge current affects this phenomenon? I have 3 of my charger pairs, so now I can charge 3.5, 7, or 10.5A, so if slow or fast charging is better it would be nice to know. Of course I haven't run out of juice since you were down, so I haven't worried about balance at all.


Sam my man, gotta edit the subject line in your first post to "Self balance charging batteries do exist, even lead batts can do that."

[CamLight]

When a pack gets out of balance after a deep discharge, then you charge/discharge conservatively for a number of cycles, and the pack gets back into good balance, what do you call it other than self-balancing?

The pack was never out of balance.
The cells are just at different voltage levels because of differences in SOC between them. Bring them all back to the same SOC and they're at the same voltage (assuming relatively good condition cells, blah, blah, blah).

If there's some sort of self-balancing going on then it shouldn't need cycling to occur. The cells would somehow "see" each other and just go ahead and balance themselves. That is, wiring a 25% SOC cell into a group of 100% SOC cells should result in a pack that has cells all at the same voltage after letting them sit. That won't happen, even with cycling the pack.

[John in CR]

When a pack gets out of balance after a deep discharge, then you charge/discharge conservatively for a number of cycles, and the pack gets back into good balance, what do you call it other than self-balancing?

The pack was never out of balance.
The cells are just at different voltage levels because of differences in SOC between them. Bring them all back to the same SOC and they're at the same voltage (assuming relatively good condition cells, blah, blah, blah).

If there's some sort of self-balancing going on then it shouldn't need cycling to occur. The cells would somehow "see" each other and just go ahead and balance themselves. That is, wiring a 25% SOC cell into a group of 100% SOC cells should result in a pack that has cells all at the same voltage after letting them sit. That won't happen, even with cycling the pack.

Of course it was out of balance, and it was still out of balance after the initial recharge. After about 10 days of 1 or 2 cycles a day then the pack returned to normal. The last time I did accidentally did a 100% discharge, was just over a year ago, when LFP was down. He even commented on the crap capacity of that initial recharge, which I think was just 7ah for the 11-12ah pack. In less than 2 weeks, the pack was back to normal accepting full capacity.

LFP already explained the mechanism, so why still argue? These Konion packs definitely get out of whack from very deep discharges just like with other lithium chemistries, and they don't return to balance at top of charge on the first recharge. It's not just a voltage difference between the cells at the bottom SOC, and the self balancing charge effect isn't strong enough to self balance charge the first go round.

[liveforphysics]

When a pack gets out of balance after a deep discharge, then you charge/discharge conservatively for a number of cycles, and the pack gets back into good balance, what do you call it other than self-balancing?

The pack was never out of balance.
The cells are just at different voltage levels because of differences in SOC between them. Bring them all back to the same SOC and they're at the same voltage (assuming relatively good condition cells, blah, blah, blah).

If there's some sort of self-balancing going on then it shouldn't need cycling to occur. The cells would somehow "see" each other and just go ahead and balance themselves. That is, wiring a 25% SOC cell into a group of 100% SOC cells should result in a pack that has cells all at the same voltage after letting them sit. That won't happen, even with cycling the pack.

Nope, perfectly matched brand new cells, at different states charge, will self balance after enough charge cycles with the spinel chemistries. They decrease charge energy efficiency and shed it as heat once they get above 4.1-4.2v or so. This makes the cells that were below this threshold get a bit of catch-up on each charge cycle until the pack finds balance.

[CamLight]

LFP already explained the mechanism, so why still argue? These Konion packs definitely get out of whack from very deep discharges just like with other lithium chemistries, and they don't return to balance at top of charge on the first recharge. It's not just a voltage difference between the cells at the bottom SOC, and the self balancing charge effect isn't strong enough to self balance charge the first go round.

LOL, not arguing at all. I think there's some confusion as to the terminology used here.
I completely agree with your statement above and was never trying to state otherwise.

LFP explained his position further and I will comment there.

[CamLight]

Nope, perfectly matched brand new cells, at different states charge, will self balance after enough charge cycles with the spinel chemistries. They decrease charge energy efficiency and shed it as heat once they get above 4.1-4.2v or so. This makes the cells that were below this threshold get a bit of catch-up on each charge cycle until the pack finds balance.

Ahhh...Interesting. Sounds very similar to charging the Nickel chemistries at over 100% SOC using low charge rates to help balance the pack. The terminology mismatch I was referring to above comes out of my thinking that the cells themselves aren't self-balancing, it's the charge that's bled off as heat that allows the other cells to catch up. The charge and charger balances them, not the cells all on their own ("self"). I guess one could argue that NiCd and NiMH cells are self-balancing too?

But, the Li stuff we're talking about is just terminology differences. The effect/end result is the same and I'll have no problems deferring to the accepted terminology used here.

[GGoodrum]

As usual, Luke has nailed it. The slight loss of charging efficiency, as the cell gets full, is the trait of these spinel-type Lithium-Magenese cells that provide a similar balancing function that occurs with lead acid and NiCds. The latter two chemistries use aqueous-type electrolytes that have side reactions that can absorb some charge current, if the voltage they are charged to is slightly above the "full" point. This can be thought of as a slight loss of charging efficiency, just like what happens with the spinel LiMn cells. The net effect is the same. some current is absorbed for a full cell, allowing the next cell in series to use that same amount of current to finish charging. This is exactly the function of most BMS shunt balancing circuits provide for other Lithium chemistries that don't have this loss of efficiency trait.

This efficiency loss is very slight, however, which is why it will take multiple charge cycles for the cells to get back in balance. As John's experience has shown, eventually they will.

-- Gary

[flathill]

When a pack gets out of balance after a deep discharge, then you charge/discharge conservatively for a number of cycles, and the pack gets back into good balance, what do you call it other than self-balancing?

The pack was never out of balance.
The cells are just at different voltage levels because of differences in SOC between them. Bring them all back to the same SOC and they're at the same voltage (assuming relatively good condition cells, blah, blah, blah).

If there's some sort of self-balancing going on then it shouldn't need cycling to occur. The cells would somehow "see" each other and just go ahead and balance themselves. That is, wiring a 25% SOC cell into a group of 100% SOC cells should result in a pack that has cells all at the same voltage after letting them sit. That won't happen, even with cycling the pack.

Nope, perfectly matched brand new cells, at different states charge, will self balance after enough charge cycles with the spinel chemistries. They decrease charge energy efficiency and shed it as heat once they get above 4.1-4.2v or so. This makes the cells that were below this threshold get a bit of catch-up on each charge cycle until the pack finds balance.

Bring this thread back from the dead as self balancing is such a great feature, but I've read more than one theory explaining how it works.

I've been doing more research on the mechanism behind this...AEA licensed the cathode to Sony and AEA's theory is cell's with a higher SOC will also have higher self discharge. This means that cells JUST SITTING THERE will also eventually self balance given enough time

The theory is confirmed:
"Tests ~8 yrs ago showed Sony HC do not imbalance
AEA developed a theory (ESPC 2002)
− Self-discharge (SD) decreases with state-of-charge (SOC)
− Cells diverge to a state of dynamic equilibrium
− Equilibrium spread depends on cell SD uniformity
Balancing model verified against test data":::::::::::

http://ntrs.nasa.gov/archive/nasa/casi. ... 015867.pdf

[parabellum]

This means that cells JUST SITTING THERE will also eventually self balance given enough time

I suppose that why I find my loose cells in the box, previously charged with single 18650 cell charger, adjusted to 4.2V, in between 4.16-4.18V after few weeks.

[flathill]

You just burned off some "surface charge"

Very few batteries will self balance as well as a few types of sony cells
Lots of batteries have chemical balancing via redox shuttling (lower charge efficiency at top end acts as overcharge protection), but the sonys have something else going on that makes the self balancing effect much greater
Must be related to self discharge vs state of charge

[parabellum]

I also overcharged 1 accidentally to 4.25V in series connection and just trow with others but then could not find this cell after few weeks, all where similar voltage (except few died self discharging cells) So they are definitively self balancing in my terms.

[John in CR]

Dumping the surface charge doesn't make any battery balance. They all do that. Luke explained it, and knows what he's talking about, end of story.

Too bad Makita improved their packs, because now the ones the Makita charger rejects aren't nearly as good as they were a couple of years ago, and they take much more work to recycle. Yet the price remains the same for packs people get for free even though overall battery prices have declined significantly. I certainly wouldn't buy any more and I love the convenience of Konions.

John

[pwbset]

Too bad Makita improved their packs, because now the ones the Makita charger rejects aren't nearly as good as they were a couple of years ago, and they take much more work to recycle.

Rats... and here I just bought 26 packs from Doc's latest offer. Maybe they are pre-2011. *sigh*

[ambroseliao]

The ones Doc sells are definitely pre 2011. No worries.

[999zip999]

Started out 2p15s sub packs up to 21ah.. Turned over to a 10p3s sub packs for a rack to 18s. 73.7v. After a week 73.7v cells 4.088-4.072v. I ran it to cutoff 62v. at 30a on my 9c 2810 got 8.71ah, 15.68mi. 37.5wh. Then checked it at 65.62v. by time I got it apart one cell ( 10p ) 3.634v then 3.646 - 3.656v all the rest. Charged to 73.7v on a turned up Ping 48v5a charger maybe 3a. all cells 4.079v - 4.089v. 10p18s. With four 4mm bullets sets in the series line to be taken out after every thing checks out. Love them for now. Till the 25 - a123's show up.

[999zip999]

Con's It took alot of makita 3.0 packs to get there, lot's of zero 0's. Water damage used and even dented inside the case ?, and the Canadian mail strike ect. Plus $$. The ah is little low so far.

[flathill]

Dumping the surface charge doesn't make any battery balance. They all do that. Luke explained it, and knows what he's talking about, end of story.
John

I never said burning the surface charge had anything to do with balancing! I'm saying Nasa confirmed the model that the self balacing is related to self discharge vs state of charge for hard carbon cobalt (not spinel) sony batteries, so more could be at play than luke's explaination related to redox shuttling or a loss in charge efficiency nearing full charge

It is interesting to me that other sony batteries also self balance, and I know you dont care
whatever end of story

[999zip999]

This bleeding or self discharge only happens over 4.1v. ? So my charging to 4.085v dosn't allow for this type of self balancing ?

[JRP3]

I think IBM was marketing a redox additive for cells that would activate at 3.9V and hold a cell at that voltage while others were still charging. Seems like a good idea, don't know if it's being used in some cells or not.

[flathill]

Not sure about IBM but 3M offers redox shuttle additives

Here is a paper that lists sony as having a 2 types of redox shuttle additives for LiMn2O4 (konion type cells)
http://escholarship.org/uc/item/39w108nw#page-3

note enerdel was working on Anode (-) Hard Carbon / Cathode (+) Lithium Manganese Oxide
Maybe we'll be able to buy them now that the Russians bought them in bankruptcy after they made a poor investment in Think

I think konion must also have hard carbon anodes as sony was the first to delvelop the hard carbon anode way back...

If so the konion may have all three self balancing mechanisms which makes them so wonderful:
1) redox shuttle chemical balancing
2) hard carbon results in synergistic self discharge vs state of charge behavior (model confirmed by nasa, cells diverge to a state of dynamic equilibrium, equilibrium spread depends on cell SD uniformity)
2) Luke's theory that spinel anodes have a sort of inherent self balance effect due to a decrease in charge energy efficiency (I haven't read this anywhere else on paper or internet but maybe it is related to the voltage plateau vs coulombic efficiencies)

[JRP3]

Right, 3M not IBM

[liveforphysics]

I never said burning the surface charge had anything to do with balancing! I'm saying Nasa confirmed the model that the self balacing is related to self discharge vs state of charge for hard carbon cobalt (not spinel) sony batteries, so more could be at play than luke's explaination related to redox shuttling or a loss in charge efficiency nearing full charge

Some mechanism causes them to bleed faster as they increase in SOC, hence decreasing efficiency (more of that energy goes into heat rather than stored charge) as they increase in SOC, and when the sit, the cells with highest SOC decrease in charge the most rapidly.

I don't fully understand the mechanism behind it, but I've observed it carefully in a number of tests and examples, and it sure is nice to have!

[999zip999]

O.k. LFP When was the last time you been in the dumpser looking konion cells ? So do I need to go above 4.1v to get this self balance burn off ??