4S3P vs. 4S2P vs. 4S1P, same mah

[Matthew_Armeni]

Sorry for yet another question, but I'm really curious on how LiPo's perform and act and don't have the money to try out all my questions So, here it is... Pack A is a 4S3P 6000mah pack, 12 2000mah packs. Pack B is a 4S2P 6000mah pack, 8 3000mah packs. Pack C is a 4S1P 6000mah pack, 4 6000mah cells. Hypothetically they are all the same size(final pack dimensions), or relatively close, and all have the same C rating. Is performance, ease of balance, pack longevity, anything else, different between these packs? In the other thread I posted people were saying cells in parrallel self balance better, that's what got me thinking about this. Thanks!

[MetalMan]

Well, a 3p pack will have more surface area than a 1p pack, which means it will shed heat faster/better.
Based on the picture I posted in the last thread, a setup like a 3p will result in a pack that is inherently better matched (will stay in balance better) than a 1p pack because each 3p group contains cells that average each other out.

[glassdoctor]

That is an interesting thought... that the 2p or 3p packs have other cells to help balance a possibly weaker/different cell. Another interesting thing is that if you did have a bad cell, it's cheaper to replace a 2000 cell than a 6000.

But I think conventional wisdom still says that few total cells equals less chance of a bad cell. In this example I would always choose the 1p if all were equal in C rating.

I don't completely agree. More cells does give more surface area, kind of. You still have the cells all stuck together and heat dissipating from the top, bottom, and sides. You really can't count the surface area that mates to another cell as heat dissipation surface. The heat is just going to transfer from one cell to another, and heat the pack up more. Also, if you had for instance, an 8000mAh 2s and an 8000mAh 2s2p, then you have one pack with 2 4000mAh cells, and one pack with 4 2000 mAh cells. In all likelihood, the 2000mAh cells are about half the size of the 4000mAh cells. In this case, 4 2000mAh cells don't have much more surface area than 2 4000mAh cells. Regardless of anything, I feel the only surface area you can count as far as heat dissipation, will be the outside surfaces of the completed pack. This is likely to be similar between two packs of the same capacity.

As Glassdoctor said, the balancing effect of multi cell packs is an interesting thought. In practice it won't really work that way. If the cells are stored for a long period, perhaps they will all bleed to the same voltage, but that does not change whether one cell in the pack discharges faster than the rest of the cells. Fewer cells in a pack will equate to having statistically less chance of a bad cell in that pack. If both the cells are matched well in a 1p pack, and you treat the pack correctly, maintaining good balance between the cells should not be a problem for the life of the pack.

The last point I can think of, is that if you take two packs of the same discharge and capacity ratings but one is a 1p and the other a 2p, the 1p pack with only 2 cells and 2 solder joints should have a lower overall resistance as compared to the 2p pack with 4 cells and additional solder joints and wiring. This should result in slightly better efficiency and less heat.

lol, anyway, i've always gone for the pack with fewer cells when it's an option.

J.

[DrKnow65]

I'll throw up the idea also, that how would you low volatge monitor all those cells in the 2000mah setup? I like using my cellshield lipo-saver as a backup to the LVC in my mamba max just incase... Seems that only using the ESC's LVC would be chancy with that many cells. I had my BEC LVC set to 3.2v per cell (9.6v) in my 3S setup and the cellshield set to 2.9 as a backup. First run of the pack and the cellshield stopped the car first. 3.4v-3.3v-2.9v, this was a total of 9.6v so the ESC LVC should have kicked out too but... if it had gone a few more tenths I would have damaged a brand new pack.

I've ran the pack a few more times and it's starting to level out on the bottom end, but the point is lipo's are expensive and I wouldn't want to run the risk of killing any. I'd go with the 1p setup and use a good low voltage devise.