Look what I found in the recycle bin

That is right, but that pic is of the German 5 cell Ridgid. Sorry, I switched which cell I was talking about.
You are correct, the 40V Ryobi is 2P10S and the BMS is in the pack.
And it’s a mother. As the series cell count goes up, with all the necessary connections between the pack and the charger, it makes more and more sense to include the BMS circuit in the pack. Safety issues aside.

Can you check on that Ridgid pack if there are balance leads going to each cell?
I recently opened a Makita pack found in the bin and found 10 Sony 1600mAh (5S2P) green cells like yours (US18650V). Can you confirm you have the same cells on the following pack pack please?

I noticed on my Makita pack that there is no balancing circuit and no balance leads! I think I know why but I want to see if your pack is the same…

There are no balance leads to each cell on the German Ridgid.



And that pack was made in 2012

That’s very interesting. It seems that these sony cells are self balancing. I did a few tests and if you charge them to 4.2V they’ll come down to 4.12V after a few hours. If you charge them to 4.1V they stay at 4.1V.
I believe that this is the reason why they don’t need balancing leads.

Interesting indeed. Thanks for the info.

lagman wrote:
That’s very interesting. It seems that these sony cells are self balancing. I did a few tests and if you charge them to 4.2V they’ll come down to 4.12V after a few hours. If you charge them to 4.1V they stay at 4.1V.

I believe that this is the reason why they don’t need balancing leads.

Hey guy. Please don't trust those any cell to be self balancing with other cells. You have a case were all you cells happen to be about the same condition at this time. A balancing circuit is for when a cell or cells start to deteriorate faster than the others in the pack.

I’m just experimenting, not trusting anything or doing unsafe things. :slight_smile:
But how do you explain the fact that the makita pack I got doesn’t have balancing leads? For a 5S lithium pack it really is a must… Unless the cells self balance. :slight_smile:

Some cells are more disposed to this kind of treatment than others. Remember, NiMH and NiCad cells were not balanced - and it’s not because they don’t get out of balance. With a hardy enough cell I think the normal strategy is to overcharge the whole pack in series and let the excess burn off as heat. A123 M1 cells (a LiFe chemistry cell) can be charged in that fashion.

I can't. Seems crazy to me. Of course, some laptops lacked adequate safety features until some hurt people. Those cells don't appear to have any protection circuits on them. Makes no sense to me, but I admit that I'm no expert by any means.

I didn't mean to imply you were doing anything dangerous or wrong.

I’m… not really sure that you’re correct about the laptop safety features thing. When I think of laptops that hurt people I think of modern machines which did incorporate BMS’s. Sony has been in the news once or twice in recent years, and it wasn’t due to a lack of BMS.

That said, low-drain cells cannot be treated in the way I describe. The only lithium chemistry cells I’ve heard can be treated this way in the past were the A123 stuff, and they are both extremely high drain and extremely hardy. (approximately: 50C pulse discharge, 30C continuous discharge, 4C charge) I can only guess that Sony’s IMR chemistry is starting to catch up enough where they can be treated in a similar way. If not, the designers of that powertool pack are grossly negligent of course…

Well, those 2 German packs had all 5 cells in each pack sitting at exactly 4.01V. They are 2 year old packs and probably cycled many times. We now know that they are not balanced charged. How else can they all be the same unless they self balance?
I just learned something today.

Remember the issue in serial batteries is not whether cells are balanced - it is whether it is safe for the cells to pass current between cells when there is an active circuit.

For example, in a 2 cell light with lithium primaries in series, if one of the cells drains faster than the other cell, then the lower voltage primary cell may start taking on too much voltage from the better cell during use - when it may not be safe to do so. Same thing with a rechargeable cell that is not in good condition within a group of cells in a series battery, especially when a charge is being applied.

I think you are trying to focus on one purpose for balancing. Really you’ve got it backwards I think. In a situation like this, balancing is all about keeping that less-healthy cell “close enough” so that the pack still operates and nothing dangerous happens. If I’ve got one cell that underperforms by 15%, over the course of several cycles we may see the cells get more and more imbalanced, unless there is some mechanism to prevent that. With a BMS we ensure that all the cells are treated appropriately and that both charges and discharges terminate properly on a per-cell level.

The cool thing about cells which can burn off excess charge is that we can overcharge the whole pack in order to get it in balance and forgo the BMS in some situations. What about discharge you say? Won’t an underperforming cell get exceptionally unhappy if we reverse charge it during discharge? Well, it would… except that this is a high drain application. We won’t run into that scenario. As soon as one cell becomes discharged ahead of the rest we’ll feel it in the tool as a lack of power and stop using the battery. Then we throw the thing in the charger and it self-balances again as the waste energy is dissipated as heat. That’s my understanding of the situation.

EDIT: So that’s the primary purpose of a BMS: to allow a pack to continue to operate with less than ideally matched cells. It’s pretty common for cells to not be perfectly matched, look at any pack-pulls thread around here for info on that. The BMS keeps the balance from slowly becoming horrible/dangerous with those low-drain cells. A pleasant side effect of having the BMS may be that it can brick the pack if one cell becomes totally terrible… but that’s not really why the BMS is present in my opinion.

I keep thinking of the recycle bin on my computer when this thread is updated and shows up in the recent posts

Wow, nice, but I think I would not be brave enough to dumpster dive the recycle bin at my HD.

Very interesting discussion.
It really is a shame that there is usually no datasheet available for 18650 cells. It would be so nice to be able to find some good data, maximum ratings and a quick description of each cell… That would eliminate the need for us to speculate like that.
Anyway, if someone is interesting and wants me to test something specific on these cells I’ll be happy to do it! (But I opened the pack and separated the cells as 2 were shorted)

It’s hard to turn down free but aren’t 1300mah and 1600mah batteries a bit small? That’s before throwing in the unknown condition of these very old things. Would they only be suitable for running things in low mode?

Hi battery.

I don't know anything about these particular cells, but most high current cells have lower capacity. They tend to be hardier and can handle more charge/discharge cycles though. Some users may have special applications that the compromise is necessary trade off.

Separately,

This whole self-balancing thing is way over my head. I didn't know it existed and am still skeptical in the case of these particular cells.

Hmm, have you considered the NiMH example I gave earler? Or maybe I didn’t. In that case: Think about NiMH series packs. They don’t get balanced, ever. That’s actually the whole story. Those cells store lots of energy, just like Li- chemistries, but they didn’t need to be balanced. Why not?

NiMH cells (as well as NiCd and Pb batteries) transform the excess energy into heat once full. That’s why they can balance on their own.
Lithium cells on the other hand, act almost like a capacitor. The voltage increases as long as you charge it. Of course, it’ll destroy itself at some point. The termination voltage (4.2V for most batteries today) is just a trade-off between capacity and security/longevity.
That’s why lithium cells (and capacitors) need to be balanced charged, to avoid any deviation that would cause one cell to be charged/discharged higher than the others.
No with the sony US18650V/VT, I noticed a very strange phenomenon, the battery “self discharges” down to about 4.1V. That also causes a battery of cells to balance by itself.
Example: 2S pack: Cell1: 3.95V Cell2: 4.05V
When charged to 8.4V: Cell1: 4.15V Cell2: 4.25V
After some time, both cells will self discharge to 4.1V. So they are balanced again.
I’m pretty confident with my observations, but it would be great if someone else could test this characteristic.

I guess you already know all that, but I just wanted to give all the facts so that we are all talking about the same thing. :slight_smile: