RCU Forums - Lipos in parallel ?

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Lipos in parallel ?

Can u help me understand how lipo cells are setup in series and parallel? As u can tell from the question i am confusing my self as i think:eek:

RE: Lipos in parallel ?

This'd be a good time to dust off a physics text book if you have one handy. But, here's what you need to know...

A battery is a group of cells.
A cell has a capacity, measured in Amp*Hours (pronounced "Amp Hours" ), abbreviated as "Ah".
A cell has a certain amount of potential to do work, measured in Volts, abbreviated as "V".

When you put cells in series, their voltage is added together. For example:

Code:

-----> [- 3.7V +] [- 3.7V +] [- 3.7V +] ----->

This battery has 3 cells in series, so this is called a "3S" battery. The total voltage of this battery is 3*3.7V = 11.1V.

When you put cells in parallel, their capacity is added together. For example:

Code:

      .--&gt; [- 1.2Ah +] --.

   ---|--&gt; [- 1.2Ah +] --|---&gt;

      '--&gt; [- 1.2Ah +] --'

This battery has 3 cells in parallel, so this is called a "3P" battery. The total capacitance of this battery is 3*1.2Ah = 3.6Ah.

You can use combinations of cells in series and in parallel to achieve different levels of Voltage and Capacitance. For example:

Code:

       .--&gt; [- 1.2Ah, 3.7V +] [- 1.2Ah, 3.7V +] [- 1.2Ah, 3.7V +] [- 1.2Ah, 3.7V +]--.

    ---|--&gt; [- 1.2Ah, 3.7V +] [- 1.2Ah, 3.7V +] [- 1.2Ah, 3.7V +] [- 1.2Ah, 3.7V +]--|---&gt;

       '--&gt; [- 1.2Ah, 3.7V +] [- 1.2Ah, 3.7V +] [- 1.2Ah, 3.7V +] [- 1.2Ah, 3.7V +]--'

This battery has 3 parallel groups of 4 cells in series, so this would be called a "4S3P" battery.
The total voltage of this battery is 4*3.7V = 14.8V, and the capacitance of the battery is 3*1.2Ah = 3.6Ah

Hope that helps.

RE: Lipos in parallel ?

Another basic question from an obvious newbie here:

Sometimes I see battery pack descriptions like "3S1P". What is the difference between "3S1P" and just a "3S" pack? Or, in other words, would that "3S1P" back be better described as a "3S2P"?

Thank you in advance.

RE: Lipos in parallel ?

I'll jump in....
3s1p = 3 cells in a series, 1p = parallel..so 3s1p is one pack of 3 lipo cells, soldered in series = 12.6 volts
3s2p = two 3cell lipo packs in parallel. This will double the Ah, but keep same voltage as the above example. I have a plane that uses two battery packs, I use a "Y" harness to double the runtime and current limit.
2s1p = two cells for one pack = 8.4 volts.

RE: Lipos in parallel ?

OK. But, why not call the 3S1P and 2S1P packs simply 3S and 2S, respectively? There is actually just cells in series there, with nothing in parallel that justifies the "1P" designation...

RE: Lipos in parallel ?

If you consistently use the same nomenclature when you're talking about LiPolys, whether it's necessary or not, you create less confusion.

"3S" has grown to mean any number of packs in parallel.

"3S1P," and you're 100% sure that you're only talking about one pack.

RE: Lipos in parallel ?

Direwolf, best explanation I have seen yet!

RE: Lipos in parallel ?

So, if I have 2 packs I want to run together to gain Mah I connector both positive and negative together? I have two 3S1P Thunder Power 2100 packs I want to install together to run a Hacker B40. I prefer keeping my smaller packs to use in other planes instead of buying a large pack dedicated to one plan

RE: Lipos in parallel ?

To Klied in response to comment on 1/13 . You say a 3S 1P pack is 3 cells soldered in series for 12.6 volts. I would have thought that would add up to 11.1 volts

RE: Lipos in parallel ?

Mac8,
You are correct. If you want to make more voltage you connect positive to negative, if you want to create more capacity, or mAh, you connect all the positive terminals together and all the negative terminals.

pikeman401,

I agree with you. I use lipos and all of my 3S1P packs are 11.1 volts not 12.6. I'm not sure where he gets that number. I'm not saying that it is wrong, but I haven't seen a 12.6v lipo. Individual cells are 3.7 volts, I thought......

RE: Lipos in parallel ?

Fortunately, the need for paralleling cells has a limited future. The newer generation of cells and integrated packs with taps will eliminate the need to parallel cells and keep the pack safe during both charge and discharge. The new technology will allow for safe charging of Lithium packs while inside the plane.

Until then, here is my two cents on series and parallel cells.

Series and Parallel Cells:

As with NiCd or NiMH cells, Lithium batteries can be wired in series to increase voltage. Also like NiCd or NiMH cells, the Lithium cells can also be wired in parallel to increase capacity and current delivery. A combination of series and parallel Lithium cells can be used to create a more capable flight pack for powering larger motors or increasing flight duration. A common designation seen to describe the configuration of multiple cell Lithium packs is the XsYp label where X is the number of cells in (s)eries and Y is the number of cells in (p)arallel.

The voltage of a single Lithium cell is about equal to three NiCd cells. A Lithium cell measures about 4.2 volts unloaded when fully charged and about 3.6 volts when loaded. The cells should not be discharged under 3 volts although it is ok for them to go below this level for short durations which may typically happen at the end of a flight until the ESC’s Low-Voltage Cut-off (LVC) or disconnect circuitry turns off the motor. The capacity of a cell is often referred to as “C”. For example, a Kokam 145mAh Lithium cell has a 1C capacity of 145mAh.

The series/parallel diagram shows one pack of four Lithium cells in series and one pack of four Lithium cells in parallel. When the cells are placed in series, the voltage per cell is simply added. The four cell Lithium pack would measure 4*4.2v or 16.8 volts unloaded. Its pack designation would be 4s1p or simply 4s. When the cells are placed in parallel, the voltage remains the same but the capacity and current delivery are added. If the four cells are the Kokam 145mAh Lithium cells then the resulting pack would measure 4.2v unloaded and have a capacity of 145*4 = 580mAh (or 4C). The current delivery capability would also jump from about 700mA continuous current per cell to about 2800mA continuous current for the 4-cell combination. The short term peak current delivery for this particular cell is about double that so our 4-cell combination would deliver about 5600mA for 10-20 second bursts. Its pack designation would be 1s4p or just 4p.

The current delivery capability of Lithium cells is different for each type of cell and manufacturer. It is often a competitive debate among R/Cers and vendors. Like the cell capacity “C”, the current delivery capability is also refered to in “C”. For our example of the Kokam 145mAh Lithium cell, the continuous current capability is about 5C and the peak current capability is about 10C. This cell was actually among the first high performance cells on the market.

RE: Lipos in parallel ?

Ok, so I have 2 Kokem 2000mah (15C) 3s packs that I've been running in parallel 3s2p but I would like to run my Axi on these but its not really enough voltage to get performance out of this motor (4120/14) so can I buy a 2s pack and add it in series for 5s or will I have to also add another 2s pack parallel? I guess what I'm saying is you can add odd number of packs in series but not parallel? so it would be 5s2p? I'm confusing myself, how about you? BG

Ron

RE: Lipos in parallel ?

never mind..think I answered my own question...DUH!

Ron

RE: Lipos in parallel ?

There should be no such thing as 3S1P but sometimes vendors want to distinguish it from 3S2P It's just 3S.

RE: Lipos in parallel ?

This is changing the thread a little but I need to ask Greg Covey if present battrey technology will soon be obsolete? What do you mean by the statement you made on 3/2. Whats coming up. I have read in other places about new battery technology. How soon will this come around. I don't want to buy a ton of lipos if the are going to be out dated in 6 months.

RE: Lipos in parallel ?

This is what I got from Greg's post: Newer cell designs will be able to handle higher loads, further reducing the number of packs you need in parallel on larger planes, PLUS Kokam will be marketing pre-built parallel packs, so you won't need to know or care about how many packs are in parallel inside that big red chunk of shrink wrap :D

Obsolete? No offense to FMA/Kokam, but no, this new technology won't make your existing technology obsolete, if anything than for financial reasons. LiPolys are still a signifigant investment, and you're not likely to throw away hundreds/thousands of dollars' worth of LiPoly to spend even more on the newer stuff. What it will do is drive the cost of the last-generation technology down, making it more obtainable. My attitude about it is, if the old stuff is doing the job for ya, it ain't obsolete...

Back to the 3S1P vs. 3S thing: Yes, a "3S1P" pack is really just a "3S" pack, but as I said earlier in the thread, if you're consistent in how you refer to the packs, you're less likely to get confused or cause confusion. 3S1P, and you're 100% absolutely positively without-a-doubt sure that you're talking about a single pack.

RE: Lipos in parallel ?

Great explanation! Similar to a 2-cell or 3-cell flashlight. You simply add the voltage of each battery because they are connected in series.

I posted a question today about the correct battery set-up for a Eflite 400 4200KV motor for a combat wing. I have been unable to find specific information for that combination.

Thanks in advance for any info.

RE: Lipos in parallel ?

That answers alot of questions for me... thanks guys...!!!

when dealing with LiPo's... that makes me alot more comfortable doing this with them. :D

I was wondering about doing this and hopping up my Ultrafly PC-9 this way. It's mean now, but now that I'm used to it... hehehe. :D

:eek: Hmmm... I wonder just HOW fast foam can fly... mmmmmahahahahahaha... hahahaha...!!!! Guess we'll find out... hehehe :D

RE: Lipos in parallel ?

As described the 3S1P is just 3S. It is just used to keep the terminology the same. Thus 3S2P and 3S3P are two and three series packs in parallel.

RE: Lipos in parallel ?

Thank you Greg and thank you Matt,

One of the hallmarks of FMA is that we try very hard to meet your needs rather than to tell you what you need. To that end, it doesn't make a whit to us if you elect to continue using our modular packs or move to our unitized packs. The connector modules will work fine with either or you might not need for the unitized packs unless you want a real "hummer" like 15S 9.6AH to fly a full scale sailplane!

While I am posting here, let us take the opportunity to remind users of the big unitized packs that you are talking a lot of horsepower, perhaps as much a 5 - 6. Even 5 horse gas enigne will generally stop or break a wood prop if you get your arm in it. A powerful high torque brushless with a plastic prop will go after your arm like a termite gone mad! So be extra careful and always stand behind the prop plane with a good grip on it when you flip that switch.

RE: Lipos in parallel ?

Far be it for me to detract from Brian Stone's excellent explanation and illustration of how 'series' and 'parallel' work in battery pack making, but I believe he actually meant 'capacity', and not 'capacitance', when referring to the paralleling of cells.

A small point, but it may be potentially confusing to some people who don't know the difference.

Rick

RE: Lipos in parallel ?

hehehe i thought i was the only one how noticed it :D

RE: Lipos in parallel ?

Has anyone tried a configuration like this? Just looking to extend flight time a little. Would an Apache 2500 charger see this as 3 cell?