i have 4 a123 packs that i have been using for a while now. i used them in my B4 and e-maxx without using a cut-off voltage. i basically drove them till the car stopped...( i never knew i had to watch the voltage on a123 cells!). one of the packs died on me and i took it apart. after that, i noticed that there is only a single wire going to the end of the pack! how can this be balancing lead?

i don't know much about lipos and a123's at all, but that looks wrong to me...

thanks,
G

p.s. the one picture shows how the battery looked before i took it apart...

That makes no sense at all. I built a pr of 5S and 6S a123s with harvested a123 cells from Dewalt 36v packs and used hyperion balance taps. The 6S takes 7 wires and the 5S takes 6 wires to connect the balance taps. My hperion 0610i balancing charger sees the cells correctly and they balance properly.

I have no idea what they are doing with a single wire. Balance tap wiring is very plainly shown here in the LBA10 balancer manual - see top of page 4 for a123s.

http://www.allerc.com/Pictures/LBA10...Manual-ENG.pdf

Do these pacs have to use their charger and they are balancing some way using main power leads and this single wire?? That doesn't seem possible either.

i forgot to mention that the charger i am charging these with, is from the same maker...ere are some pictures.
i don't get the whole balancing thing anyway?! why don't nimh or nicd's have to be balanced? anyhow, let me know what you think...

thanks,
G

It appears that charger does use the main power leads as part of the balancing setup. On the typical three wire 2s balancing port two of the wires are connected same as the main leads. Only drawback I can see would be a possible slight voltage error due to different wire resistance.

The reason balancing is not required with nicads & nimh is because those cells don’t normally burst into fire if overcharged a little. (explode maybe, but not burst into flames lol)

It would help them though, reduce heat build up. Spintec makes a charger with 6 separate floating ground charge channels that accomplishes the same thing.

http://spintec.nl/ICC.shtml

thanks for the info...very helpful...

G

Little diff take on why lipos are balanced - if you overdischarge lipo, you can potentially ruin it (a cell swells or puffs) and once that's happened, its unsafe to either charge or to use. To keep from overdisch one cell, balancing starts them out at the same voltage so the chance for overdisch is minimized as much as possible.

Builtin esc low voltage cutoffs look at total voltage not individual cell voltage so if cells start off unbalanced, potential is there to overdischarge a cell while the lvc still sees enough voltage to let it continue to run.

You don't have quite this potential for damage with the other chemistries.

Well, maybe so...

But if they aren't balanced on the charging end you won't have a chance to worry about your low voltage cutoff.

They are kinda hard to strap in when they are on fire!

sounds logical to me...thanks for the info.

G

p.s. i still wonder why cells discharge or charge differently. does it have something to do with there internal resistance?

There are variations in the manufacturing process of just about anything, including battery cells.

Regarding low voltage cutoff, this is why the LVC is typically set at a value well above the actual cell limit, on the order of 0.3 volts or more, to account for some differences/variations in cells. Also this occurs at a time where the voltage is dropping fairly rapidly, a slightly higher cutoff causes little reduction in run time. It has been noted by others, packs that aren’t well matched need a higher LVC setting to prevent damage. Even if balanced.

Charging goes much closer to the actual cell limit, typically 0.05 volt, and is held there for quite some time during the charge process. Thus the importance of balancing on that side, or at least a well matched set of cells to begin with as some rely on. Otherwise the pack goes up in flames, many youtube videos are available if you're interested.

thanks for the fast reply...i have one more question, but it has to wait till later...( don't have the time to ask right now as it is kinda complicated...)

This is the difference in price between a lipo like an Orion for example and a lipo off Ebay thats less than 1/2 the price. In the better lipos, the cells are closely matched and in Kokam's case their manufacturing process from the start is geared toward producing cells of near identical character. Better quality cells will tolerate more abuse (discharging to a higher percentage of capacity, doing it more often and slight overdischarges) than lower quality cells.

Have to be more careful with cheaper lipos than with higher quality lipos. Don't get me worng, you can damage the better quality lipos too, but its usually not fatal (don't swell) - you just get fewer cycles from them.

makes total sense to me...i could have come up with it myself,ha ha

one more thing:

i want to get a new charger, not sure what to get though...here is the question: if i get a new charger and want to start using my a123's with it, i would have to put balancing leads on them or could i charge them without the balancing lead since a123 cells are able to take more abuse?!

the other thing is: why do cells not balance each other themselves?! i am not an electric wizard but wouldn't it make total sense to assume that if you connect to cells to each other, one with more voltage and capacity then the other, they start balancing each other? i am not sure if i am explaining it correctly but it should be like having to buckets connected with one pipe to each other...the capillary principle (not sure what its called in English)would cause the water level to be the same in both buckets...

thanks
G

That would be true with a parallel connection, for more capacity. Not with series connection, for more voltage. Think of the water buckets on top of each if you will, they won't balance each other then.

Wrong analogy. Imagine two buckets, each with a hose connected to a pump. If one bucket has 1 gallon of water and the other has .75 gallons the .75 gallon bucket is going to run dry sooner.

Also, when cells are connected in series there seems to be some slight differences in discharge rate depending on where in the pack a cell is. Not sure why but with NiMH and Nicd it always seems like the cell with the negative power tap dumps first.

good point...but water cant flow upstream due to gravity...electricity doesn't have that problem...but i get the point.

thanks,
G