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 Is it better to have more cells in a Lipo battery?

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Wolfleader
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PostSubject: Is it better to have more cells in a Lipo battery?   Fri Aug 11, 2017 8:24 pm

Something I've sorta been wondering about as I was browsing for some lipo batteries a couple of days ago.   

So lets say you have 2 different batteries.  One is a 2 cell 5000mah 7.4v lipo and the other is a 6 cell 5000mah 7.4v lipo.  Would there be any noticeable difference between the two?  Does it get better or worse the more cells you have in a lipo battery or is there no difference at all performance wise.

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Jughead
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PostSubject: Re: Is it better to have more cells in a Lipo battery?   Fri Aug 11, 2017 9:07 pm

I don't think they make a 6 cell 7.4 lipo , a 2 cell 5000 or 5500 is just right for a rc tank , you could play all day without a charge , even a 3s is too much for a tank , the stock wiring in a tank can't take the juice and amps , besides the 2s 5000mah lipos are much cheaper to buy ! Local hobby shops usually sells them from 40 to 60 bucks , for a mid grade lipo
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PostSubject: Re: Is it better to have more cells in a Lipo battery?   Fri Aug 11, 2017 11:07 pm

Jughead, I think Wolf is talking about the physical number of cells in a lipo battery, not the virtual number of cells. You can have a 2S lipo which basically consists of two 3.7v virtual cells, but it could have 3 physical cells wired serially to give you 3.7v, and then the two sets wired parallel to give your 7.4v, or 2S.

Assuming that you know the number of cells in your lipo, they would be wired to behave as a 2S anyway so I am not too sure if there is any material difference. Most of the time these days you don't actually know the number of cells in a lipo pack, only the virtual cells (i.e. 2S vs 3S) so I am not too sure if you can even determine there is material difference.

I think the only downside might be cells getting out of range from each other and your charger could refuse to charge them as a group. Logically speaking the more number of physical cells you have, the higher the chance of one of them getting out of sync with the others.
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PostSubject: Re: Is it better to have more cells in a Lipo battery?   Sat Aug 12, 2017 10:39 am

Lipo terminology... think of a grid/table.

example: 2S2P

First number followed by 'S' is the cells in series 3.7V per cell, so 2S = 3.7V * 2= 7.4V
Second number followed by 'P' is the cells in parallel which equates to additional current discharge rates. So 2P = 2 cells per 'S'.

The above would have a total number of cells of 4, but is measured as a 2S for voltage.

From RCGroups.
Quote :
4.10C from 3S4P? Naming conventions explained.
How fast a battery can discharge is it's maximum current capacity. Current is generally rated in C's for the battery. C is how long it takes to discharge the battery in fractions of an hour. For instance 1 C discharges the battery in 1/1 hours or 1 hour. 2 C discharges the battery in ½ or half an hour. All RC batteries are rated in milli Amp hours. If a battery is rated at 2000 mAh and you discharge it at 2000mA (or 2 amps, 1 amp = 1000mA) it will be completely discharged in one hour. The C rating of the battery is thus based on its capacity. A 2000mAh cell discharged a 2 amps is being discharged at 1C (2000mA x 1), a 2000mAh cell discharged at 6 amps is being discharged at 3C( 2000mA x 3).

All batteries have limitations on how fast they can discharge. Because of this many LiPoly batteries are put in parallel to increase the current capacity of the battery pack. When 2 batteries are wired positive to positive and negative to negative they become like one battery with double the capacity. If you have 2 2000mAh cells and you wire them in parallel then the result is the same as 1 4000mAh cell. This 4000mAh cell has the same C rating as the original 2000mAh cells did. Thus if the 2000mAh cells could discharge at a maximum of 5C, or 10 amps then the new 4000mAh cell can also discharge at 5C or (4000mA x 5) 20 amps. This method of battery pack building allows us to use LiPoly batteries at higher currents than single cells could produce.

The naming convention that allows you to decipher how many cells are in parallel and how many are in series is the XSXP method. The number in front of the S represents the number of series cells in the pack so 3S means it's a 3 cell pack. The number in front of P means the number of cells in parallel. So a 3S4P pack of 2100mAh cells has a total of 12 cells inside. It will have the voltage of any other 3S pack since the number of cells in series determines the voltage. It will have the current handling of 4 times the maximum C rating of the 12 individual cells. So say our 3S4P pack had a maximum discharge of 6C. That means that it has a nominal voltage of 10.8 volts (3x3.6) and a maximum discharge rate of 50.4 amps (2100mAh x 6Cx4P ).
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PostSubject: Re: Is it better to have more cells in a Lipo battery?   Sat Aug 12, 2017 10:23 pm

Ahh I get it.  I always sorta thought the S stood for Cell for some reason not cells connected in serial which sorta threw me off once I started seeing 2S3P in some battery packs.

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PostSubject: Re: Is it better to have more cells in a Lipo battery?   Sat Aug 12, 2017 10:30 pm

MikeC wrote:
Jughead, I think Wolf is talking about the physical number of cells in a lipo battery, not the virtual number of cells. You can have a 2S lipo which basically consists of two 3.7v virtual cells, but it could have 3 physical cells wired serially to give you 3.7v, and then the two sets wired parallel to give your 7.4v, or 2S.

Assuming that you know the number of cells in your lipo, they would be wired to behave as a 2S anyway so I am not too sure if there is any material difference. Most of the time these days you don't actually know the number of cells in a lipo pack, only the virtual cells (i.e. 2S vs 3S) so I am not too sure if you can even determine there is material difference.

I think the only downside might be cells getting out of range from each other and your charger could refuse to charge them as a group. Logically speaking the more number of physical cells you have, the higher the chance of one of them getting out of sync with the others.

Yeah, that was pretty much what I was wondering about.  Like what advantages if any does having more cells have.  So what are the difference between physical and virtual cells?  I mean physical cells obviously means the actual physical battery cells that are connected together but not really sure what virtual cells are.

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PostSubject: Re: Is it better to have more cells in a Lipo battery?   Sat Aug 12, 2017 11:38 pm

Sorry I just invented those terms to describe lipo cells. All the cells (physical ones) in a lipo is 3.7v norminal, and I think can go as low as 3.1v or as high as 4.1v. When you link them together serially, you will get a what we call 1S (wrongly called 1 cell lipo) which gives you 3.7v. So you can have one cell, or 10 cells, as long as they are wired serially together, you will get 3.7v output, or what we call 1S/1 "cell" lipo.

When you wired these groups of serially wired cell together in parallel, you will get 2S, 3S, 4S etc lipo, or what we call 2/3/4 cell lipo. 

So when we say 1 cell or 1S lipo, what we really mean is that there is a group of batteries (one or more) wired together serially providing 3.7v of output. When we say 2 cell or 2S lipo, there is TWO groups of batteries (one or more) wired together in parallel to provide 7.4v of output.

The old nomenclatures of P is the number of physical cells wired serially. However, these days most lipo only tells you the groups of cells that are wired parallel together as most application only need to know the total voltage which is basically on the number of groups of batteries wired parallel. You don't see the P nomenclatures much anymore.
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