I haven’t tried this.

[KnowAir]

I guess all I was tryinig to say is 6 cells in series is 6 cells..ie, "if" the restistance adds up with each cell, whether using a 6s "brick" pack or 2x3s, still 6 cells in series. As such one cell will always see a different amount of resistance versus another that it's wired to. I can accept that a 6s brick presents the "lesser" of two evils, meaning that having to use multiple cells in series to develop the voltage desired will never be the ideal setup..

 

[tudordewolf]

Nobody is denying that uneven wear occurs even in well-balanced packs.

Nobody is denying that putting cells in series adds up their internal resistance across the battery.

What SMC implies is that something about putting cells in series increases the resistance of subsequent cells, and this is the mechanism that leads to uneven wear. They could've said something about uneven heating, internal jumpers, or resistance from extra connectors, but they chose to word it very specifically as if latter cells in a series string experenced higher internal resistance within themselves because of their location.

Maybe that's not what they meant to imply, but that's how it's worded, and that's what's being contested.

It makes lots of sense that once one cell has a higher internal resistance, it will wear out more quickly than the others, but that isn't a product of it being "latter" in the stack.

 

[KnowAir]

Nobody is denying that uneven wear occurs even in well-balanced packs.

Nobody is denying that putting cells in series adds up their internal resistance across the battery.

What SMC implies is that something about putting cells in series increases the resistance of subsequent cells, and this is the mechanism that leads to uneven wear. They could've said something about uneven heating, internal jumpers, or resistance from extra connectors, but they chose to word it very specifically as if latter cells in a series string experenced higher internal resistance within themselves because of their location.

Maybe that's not what they meant to imply, but that's how it's worded, and that's what's being contested.

It makes lots of sense that once one cell has a higher internal resistance, it will wear out more quickly than the others, but that isn't a product of it being "latter" in the stack.

Well said, this was my inquiry. The way SMC had worderd it is misleading I feel. I can certainly believe what Bill has said as well with regards to one pack generating more heat than the other.. I never checked them with my temp gun, but have noticed one pack "warmer" than the other when wired together.. I'm terrible when it comes to battery management I'll admit. I mix n match packs alot. Mind you, they are packs of the same brand and specs, just not always run together or rotated as has been mentioned here.
I'm working on that though.. trying to keep batteries in "pairs" and not use them independently in another rig.
Perhaps one day I can have batteries of each needed voltage to use in my various models, ie 2,3,4 and 6s packs.

 

[Jerold]

Jerold, I know all of that. I studied electronics for 4 years. Now a scientific article OR ANY OTHER THING IN THE WORLD that mentions what SMC claims would be nice.

SMC (https://www.smc-racing.net/index.php?route=product/category&path=166)
This is due to the flow of current, the current from one pack must flow ‘through’ the second pack meaning that the current sees virtually double the resistance of the first pack. As you read below about the ESC cutoff, the pack with the highest resistance will drain the least. The ideal setup would be to run 1 pack at the proper voltage instead of 2 packs in series to get the desired voltage. This is why we offer 6S packs that fit in the Arrma 2018 battery trays as Arrma allows the use of one 6S pack instead of two 3S packs.

I see what you mean. Basic modeling of two 3S packs with a connector is the same as one 6S pack, volts is volts and IR is additive. So I don't necessarily buy the argument that the single 6S packs has a lower IR while running. Engineering says you will have shorter leads and less resistance but that's in the µΩs and it's well outside your standard DVM accuracy. How is it different inside the pack from an external connector?

The reality is that this is a highly complex chemical reaction and can't be modeled with a simple resistor and a battery cell. The companies have well developed models (probably in Matlab and or SPICE) are considered proprietary and they wont' share them with us. The IR is dynamic and a function of many variables, more than I know.

Purely a guess here. Because this is not resistor, but a chemical process, it may exhibit other behaviors when current is run through it, rather than sources from it. It would have to give and get electrons as the same time. Because current is entering the battery it might have a charging effect? I dunno, again purely a guess, so don't quote me no that.

In the end, it might be snake oil or it might be true but good questions.