2s2p vs 2s1p

[kookie_guy]

Is there any difference in performace/safety/charging of a 2s1p vs a 2s2s pack? Here's the ones I'm asking about...

http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=14989

They are the only 40c ones that are available at the US warehouse.

[domp444]

I'm no battery professional, but the battery should work just fine. All it is is 2 batteries in one case running parallel, and in both of those batteries there are 2 cells running in series. All it is doing is combing two 2500mah packs to make one 5000mah pack. I don't see a problem!

[kookie_guy]

I'm no battery professional, but the battery should work just fine. All it is is 2 batteries in one case running parallel, and in both of those batteries there are 2 cells running in series. All it is doing is combing two 2500mah packs to make one 5000mah pack. I don't see a problem!

I agree, my only concern is that are both of those 40C rated? Or are they 20C each, and hobbyking does not realize that the C rating is not doubled when you put it in parallel. Because then it would still be 20C.

[domp444]

I agree, my only concern is that are both of those 40C rated? Or are they 20C each, and hobbyking does not realize that the C rating is not doubled when you put it in parallel. Because then it would still be 20C.

Very good point!

[kookie_guy]

Anybody elese with any insight? Perhaps people who own them and can confirm the 40C rating. I e-mailed hk with the technical question. Let's see if they actually understand what I'm talking about. lol

[driftah]

the c rating on those batteries tends to be a bit overrated imo maybe about 75% of the number possibly

[chuff]

Anybody elese with any insight? Perhaps people who own them and can confirm the 40C rating. I e-mailed hk with the technical question. Let's see if they actually understand what I'm talking about. lol

The error comes when we (they) confuse cell C rating with pack C rating.

A 2S1P pack made of two 20 C cells will remain a 20C pack. Make a 1S2P out of the same two cells and you have a 40 C pack.

The problem is who can be sure what the manufacturer actually means. Is he describing the cell C rating or the pack C rating. I guess we can really only take him at his word and assume he is talking about the pack rating since his label is on the pack and not the cells.

[Fluid]

The error comes when we (they) confuse cell C rating with pack C rating. A 2S1P pack made of two 20 C cells will remain a 20C pack. Make a 1S2P out of the same two cells and you have a 40 C pack...

Confused? Yep, this poster sure is. Paralleling two 2S packs does not change the total "C" rating. That is a characteristic of the cells themselves and has nothing to do with pack configuration. Paralleling does double the pack's capacity, but not its "C" rating. So a 2S2P pack made from two 2S/5000mAh/40C packs has a total capacity of 10,000 mAh but still has a 40C rating. It can safely discharge at 300 amps continuous using the 75% rule: 10 amps x 40C x0.75 = 300. Otherwise by the poster's understanding the pack would be good to 600 amps. Not.

But as has been mentioned, are the cheap cells REALLY 40C? The consumer can't reliably measure that, so the sellers are free to say what they want to say. I've seen too many Turnigy packs which by the label are good to 300 amps, burn up in setups that safely run 25C ThunderPower packs. I don't know what their true C rating is - but I do know that it is a lot cheaper for the seller to print a label than to offer better cells.



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[kookie_guy]

Confused? Yep, this poster sure is. Paralleling two 2S packs does not change the total "C" rating. That is a characteristic of the cells themselves and has nothing to do with pack configuration. Paralleling does double the pack's capacity, but not its "C" rating.

Agreed, I already commented on his post in the C rating thread, that's he's completely wrong on his thinking.

[Jeff Wohlt]

It does not change C rating but you can draw more amps when in 2P.

So 5000 x 20C gives you 100 amps but in 2 P can give you closer to 200 amps but you never want to max that out so I say at least it would be good for 175 amps peak. I also never figure a burst rating either. If anything I will use a little bit lower C value on my packs to figure it. I figure my 30C packs as 25C to be safe. Or 40 to about 30-35. This gives you a safety net.

[chuff]

Hmmm... my mistake, talk about shooting yourself in the foot!!. :doh:

My mistake was trying to keep the discussion too simple. I have consulted with my Electrical Engineering colleagues. They know what they are talking about and have suggested explaining the issue as follows:


Let’s say we have a battery made up of two cells in series (our 2S1P configuration)

Lets also assume the label on the battery is accurate when it says “5000 milliamphour, 25 C, 7.4 volt”

From this label we interpret that the 1C current is is 5 amps, and the “safe” max current is (allegedly!) 25 C or 125 amps.

As the battery is series wired, the label also means that each cell in the battery must be a 5000 mAhr cell. This is because 5 amps will theoretically fully drain (or charge) either the battery or an individual cell from the battery, in one hour (the voltage during the current drain of course would be different)

Now, on the other hand, if we cut the battery apart and the same two cells are now wired in parallel to make a new battery (a 1S2P configuration), how should the new battery be labelled?

Is it still a 5000 mAhr battery or has it become a 10,000 mAhr battery?

The answer is that it is, and should be labelled as, a 10,000 mAHr battery , as the 1C current has now become 10 Amps.

The “safe” current out of the battery will have become 250 amps, so the label should read

10,000 mAhr, 25C 3.7 volt

So, as others have corrected me, the C rating is still 25C. Of course, what our Chinese friends actually write on the label is another matter.

Note that ignoring minor differences between individual cells, the safe current from the battery is 250 amps ie twice the safe current out of the series-wired battery built out of the same cells.

Chris