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

[SamTexas]

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 title "Data sheet for SELF-BALANCING 18650V" changed.

 

[BatteryMooch]

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

No cell can self-balance as no cell can be aware of the SOC and resting voltage of the other cells. Has never happened and never will. So you won't be able to find any data on this.

Having said that, there are some cells that are manufactured to tighter physical tolerances using chemicals also having tighter manufacturing control over their content (i.e., they're "purer"). These cells will, of course, go out of balance eventually but the tighter manufacturing control helps to extend the time they will take to get out of balance enough to be a problem.

Essentially, the cells that are purported to be "self-balancing" are just better matched due to tighter control during manufacture. They will all drift and age, but often at a slower rate than others and will tend to do so as a group and not all over the place as often happens when using other cells. But, of course, this is only true if pack assembly doesn't impact the cell-to-cell uniformity....which it does.

Only testing can help each user to decide if a pack using these cells will stay balanced long enough to not exceed whatever limits we set for pack performance.

 

[Doctorbass]

Here is the TRUE specs i found on the internet back in 2007.

They was erased from the website few weeks after.

As far as i know.. .I remain the only source of these specs over the internet :lol:

They made a mistake.. at 1C the Wh IS 5.61Wh... not 3.61Wh... just pay attention to that to avoid confusion....

Here it is:
:wink:

Doc

 

[SamTexas]

I have seen that specs before and there was nothing about self-balancing. I just looked again at the specs you attached and again no reference to SELF-BALANCING. What gives?

 

[BatteryMooch]

Umm...because they don't self-balance?

 

[SamTexas]

Umm...because they don't self-balance?

Exactly. So why do people buy and use these cells without a BMS? May be for the same reasons I do with my home built Lithium-Cobalt pack at this time. But I have no illusion that my pack would stay balanced for long.

 

[Doctorbass]

These battery are known since 2006 and have been tested also by the Nasa Aerospace flight program.

They have been used in makita, Bosh and Bionx stuff

each of these conpagnt DONT have any balance lead or balancer in their battery

Only the new Makita 2011 have balance lead but they use the same cells.. they just decided to help prolong their pack like a bit and reduce the deffective pack duw to lower cells vs aging

I dont know why people sday they self balance... it'S not the afct...

They just DONT NEED balancing.. but they must be protected against over dishcarge and overcharge to avoid damaging them

They are as safe as A123 cells

 

[Doctorbass]

Here is an interesting thread i made for them:

http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=27707&p=400378#p400378

Doc

 

[SamTexas]

I dont know why people sday they self balance... it'S not the afct...

They just DONT NEED balancing..

Huh???

 

[BatteryMooch]

All cells don't inherently require balancing. It all depends on the cells and how they're used. For example, if I have a hi-capacity A123 pack, keep all of the cells at the same low room temperature all year around, only charge them to 3.5V/cell at a 0.5C rate and only discharge them at 0.5C down to 3.3V/cell, those cells won't become anymore unbalanced for years.

If I'm using even lower internal-resistance cells with even tighter manufacturing tolerances, then I can abuse them a lot more and still not need balancing before the cells reach their end-of-life.

So, some cells don't need balancing for a lot of applications. But, lots of cells need balancing for some applications.

 

[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?

 

[John in CR]

I suspect the cause to be self discharge varying with voltage to an extent that is different from other batteries. ie Higher voltage has greater self discharge, causing the string to naturally come back into balance.

 

[trademybikes]

Its likely a chemical additive protecting from overcharge, results in balanced. This topic was posted last December, the General Motors Lifepo4 patent. Within the patent is ALL the other chemistries that also work. Its 5.5 years since all was known to the inventor group & put to paper. 5 years for patent approval.

How many years has the method been used & by whom? Did the university/GM enter agreements pre-patent? Stolen tech? Does the patent intent to eliminated copies? 20 grand cash bribes most formulas...in general.

Long term players will recall when specific battery types quit burning easily (hint LiFePo series). Recent posts indicate which "Li-ion" sources/suppliers its NOT in.

Dwell on it.

 

[liveforphysics]

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.

 

[Doctorbass]

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...

 

[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 :lol:

 

[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."

 

[BatteryMooch]

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.

 

[BatteryMooch]

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.

 

[BatteryMooch]

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.ntrs.nasa.gov/20080015775_2008015867.pdf