If a battery is listed "2P"...

[Harrisy]

So I was having this discussion with no brother and some friends. My general understanding has been that if a battery is listed as "2P", you double the mAh. For example, we all ordered the SMC 6500mah 6S2P. I was telling one of our friends that this means it's really 13,000mah. My brother questioned it and said he thought it was two 3250mah packs together. I tried to argue my case, but truthfully other than some Google searches, I am not 100% sure. I do know that my 7200mah 6S2P is almost twice the size of a 5000mah 6S1P.

Now with this being said, why don't they just list it as 13,000mah or whatever it comes out to? What's the benefit of wiring in parallel? I thought maybe it was a way to keep the size of the pack down. I have no science to back this up, just couldn't think of any other reason. I'm really just trying to understand this so any information is appreciated.

 

[martysmith223]

So I was having this discussion with no brother and some friends. My general understanding has been that if a battery is listed as "2P", you double the mAh. For example, we all ordered the SMC 6500mah 6S2P. I was telling one of our friends that this means it's really 13,000mah. My brother questioned it and said he thought it was two 3250mah packs together. I tried to argue my case, but truthfully other than some Google searches, I am not 100% sure. I do know that my 7200mah 6S2P is almost twice the size of a 5000mah 6S1P.

Now with this being said, why don't they just list it as 13,000mah or whatever it comes out to? What's the benefit of wiring in parallel? I thought maybe it was a way to keep the size of the pack down. I have no science to back this up, just couldn't think of any other reason. I'm really just trying to understand this so any information is appreciated.

my guess is the same as your brothers two 3s packs vs 6 individually wired cells not positive but it makes more sense I guess

 

[Erstadw]

Have you tried emailing smc? They usually respond pretty quick for me. Most times same day.

 

[nino]

WROOONG. It's two smaller cells in parallel. Do you really think anyone would sell you a bajillion mAh and not advertise that on the box but use a number half of that?

So, 6 pairs of 2 cells in there.

 

[arrmadillo]

No, not 13,000 mah!
6s is 6 cells in series, 1 cell in parallel 1p
so 6s1p has 6 cells total

6s2p is 6 cells in series but each of them cells in series is made up of 2 cells connected in parallel.
So a 6s2p pack has 12 cells in it. But are wired in a way to give 6s voltage.

I always use 1p packs because of the lower cell count.
A 6s2p pack has 12 cells, twice the chance of a cell going bad of a 1p pack. Then there's they added weight or size of a 2p pack especially in 6s size with high mAh.

 

[Lazy Bushman]

As per what @arrmadillo said. I’m pretty sure that all mine are 1P but I didn’t deliberately set out to do that. If I saw a 2P battery at a good price then I would still buy it. In theory 1P is better but I doubt the difference would be material

 

[nino]

Yeah, I never liked the idea of 2p packs, you can't really check each individual cell's health.

 

[Lazy Bushman]

Agreed and connecting the additional cells does introduce more resistance. All that said, if they were cheap enough I'd still buy. I don't check my cells all that often anyway and given they are in parallel then if they are particularly bad, you should still see some variation between the different parallel pairs, if that makes sense, however it would hide a dodgy cell for longer I reckon, but I don't have any practical experience with them to be sure

 

[Harrisy]

Okay, but what is the benefit of having a 2P pack then? From what you guys say, seems like there's nothing but downsides to it compared to a 1P. Bigger pack, higher chance of damaged cells... So why even make the damn thing?

 

[nino]

Two 30C cells in parallel make a 60C cell. Think that's the main reasoning. More current capacity.

 

[Harrisy]

Two 30C cells in parallel make a 60C cell. Think that's the main reasoning. More current capacity.

Okay, that makes sense. Thanks for all the info guys!

I think my confusion came from reading multiple articles about this. I didn't differentiate between one pack being sold/wired as a "2P" vs running two separate packs in parallel (i.e. with a parallel adapter)

 

[olds97_lss]

Odds are, it's also cheaper to have a 2P pack. The assembler can take 2 cheaper lower MAH/current cells to make a higher capacity/current "cell". Having 2P packs also doubles the chances of dropping a cell in any given pack.

 

[arrmadillo]

Okay, but what is the benefit of having a 2P pack then? From what you guys say, seems like there's nothing but downsides to it compared to a 1P. Bigger pack, higher chance of damaged cells... So why even make the damn thing?

From what I understand, the higher the mAh or higher the power of a pack, the thicker the cells need to be. Thicker cells can increase the chance of issues with the sealing of the pouch.

So instead of having cells 10 or 11mm thick, they make them 5.5mm thick to prevent possible issues with sealing.
This is the reason for a 2P pack with more cells.

 

[Harrisy]

Thanks guys. Cancelling my 2P pre-order and getting a 1P pack!

 

[slick2500]

Two 30C cells in parallel make a 60C cell. Think that's the main reasoning. More current capacity.

Nope. Still only 30c. C rate does not scale.

 

[olds97_lss]

Nope. Still only 30c. C rate does not scale.

It's kind of weird and messes me up whenever I think about it unless I write it down. lol

Like for the following:
5000mah * 30C = 150A

If you take 2 of the same cells in parallel, the cells are still 30C, but the pack can output 300A with a voltage of 4.2V.
(2*5000mah) * 30C = 300A

So, the "C" rating of the pack doesn't increase, but current capability does. As does run time of course.

Then if you do the same, but wire in series, the amps stays the same as the single cell, just the voltage increases.

 

[nino]

^ this.
2 capacitors, car batteries, anythings in parallel can dish out twice the current.

 

[chevys10zr2003]

^ this.
2 capacitors, car batteries, anythings in parallel can dish out twice the current.

That is correct that it doubles the current but it doesn't change the C rate and that's what @slick2500 was correcting you on.

 

[nino]

Well fiddlestick me, my brain malfunctioned a bit there.

Carry on. ?

 

[olds97_lss]

Well fiddlestick me, my brain malfunctioned a bit there.

Carry on. ?

Yeah, that's kind of what happens to my brain any time anyone asks that "parallel vs series" question. First instinct is to say "yes, c rate doubles" when really, the C rate is the same, just the current that doubles.

I think C rate existing at all is what makes it confusing. If they just rated packs in constant/peak amps... then it wouldn't matter.