Running Packs in series or parrallel
 

I have a question that doesn't pertain to me since I run single packs but I'm curious and I figure you guys know LiPos better then most so here it is-
If I'm running 2 LiPo packs, in an E-Maxx let's say, is it better to A-run 2 2S 8000 packs in series or B-run 2 4S 4000 packs in parrallel? And could you explain why one is better, or why they are the same? Or how about C-run a 4S 8000 saddle pack? Thanks!

A.

The way I see it, four groups of two (4x 1s2p) is better than eight groups of one (4s1p x 2). Each of the cells in the 2p groups are paired up with another cell, and stay that way. In 2x 4s1p, none of the cells are paired up, so they aren't averaged out. Like with 1s2p x 4 the cells in the 2p pairs are "averaged" out with another cell.
It's hard for me to explain through words. If you don't understand what I am trying to say, then I can further clarify.

Yes, Would you please explain further. I have had this question on my mind a number of times.
Thanks

When it comes down to it, there is no performance advantage between the two configurations in your example. Both examples have a total of 8 4000mAh cells. The only difference is the way you arrange them. Personally I would rather have a 4S1P 4000mAh pack than a 2S2P 8000mAh pack as a I would have more use for a single 4S pack than a 2S pack. For example, I could run a single 4S 4000mAh pack in my Ofna CRT.5 and later run both 4S packs in parrallel in my Revo.

A potential issue could be your charger's capabilities. If your charger can not handle 4S then you will either need a new charger or run the 2S2P configuration.

From a practical standpoint, one might be better just based on how you could use the packs, as starscream said.

Electrically it makes no difference... all three examples do exaclty the same thing.... EXCEPT... that example "b" doesn't have the advantage of having the cells paired up in "2p" sets. This essentially makes each set of 2 cells into a single cell that will balance itself.

(This assumes that in example "c", it's built in a standard method by first making 4 sets of 2 cells in parallel, then running those 4 sets in series.)

In example "b"... you have twice the odds of a cell going out of balance because you have 8 individual cells rather than the effective 4 cells in examples "a" and "c".

The other guys have already said the same thing, in other words.

Having said all that, I like the flexibility of having two 4s 4000mah packs if you have a use for them. But then, I built mine as a single 4s 8000mah pack. lol

Hmm, from my perspective example B and C, from the original question, are identical as a saddle pack would be 2 4S 4000mAh packs. In regards to 4 2S packs, that would be very impractical, hard to manage, and would be a last resort imo. Using more than two packs on a car would be an ineficient use of resources.
I don't know too many folks that are concerned about keeping Lipo cells balanced during discharge. As long as you are using a low voltage cutoff and a Balancing Charger, a 1P configuration will always be ideal. Thats my 2 cents anyway

LOL... I didn't notice that he said saddle pack... my bad.

A saddle pack could be made in either method (a or b).

I was referring to "c" as a single pack.

Well C would be a single pack (in a sense) because there'd be one connector and one balancer. I read on TrueRC that when assembling multi P packs that you should solder them all in parrallel first then in series, which seems to be the consensus here. I drew up a pic on paint for some visualization, one without balancers and one with. Not the best drawing I know, but you can see what I'm talking about.

http://inlinethumb38.webshots.com/31...600x600Q85.jpg

http://inlinethumb04.webshots.com/31...600x600Q85.jpg

glassdoctors's explanation for B looks like it fits A, and is a good explanation for what I was trying to get to. Here's a pic to further demonstrate why I choose A (B is on the left, A is on the right):

Although, the each pair of parallel cells in MM's right pic would not have the different voltages as shown.

I too think it's best to make your P groups first, and then put those in series. Plus, balancing as a whole is MUCH easier.

Wow
 

Now that is quite a pile of info to absorb. It looks simple enough, but if you look at it long enough it can really get confusing. Thanks guys for all of that. I think I am begining to udnerstand. Like most things in the engineering field we may learn this best by building some on our own, with a little assistance of course. Thanks for sharing this with us.:lol:

Exactly, just showing how any out-of-balanced cells are averaged out by the cell they are paired with.

And yes, balancing is a hell of a lot more simple.