Serial LiPo Battery Arrangment

To make a 14s battery I am considering combining 2 x 6s + 2s. As long as they have the same C-rating and capacity, this is fine to do right?

and it should also be fine to mix manufacturers?

To me it sounds like asking for trouble.

I would be wary of mixing manufacturers as slight differences in cell characteristics will lead to uneven wear and likely premature failure of one of the batteries.
For single manufacturer I would contact them to make sure they use one cell model for both batteries.

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that makes sense. i was just going to daisy chain hobbyking lipos. no customer support there :sweat_smile:

I see Pulse makes a 14S pack in an odd size. I have used other Pulse batteries and they have performed well. How much total capacity do you want?

looking for about 5000-6000 mAh

They have a 5000mah. Big $$$

Pulse 14S

Just noticed it’s actually 2,7S batteries in one pack but they bring the leads out for serial connection and 7S charging. So of course they have 7S packs too!

this is a great option, but yeah a bit too pricey. The nominal Wh/kg is not bad at 147 Wh/kg. I could probably build a similar 14s from 6s+4s+4s for less than half the price, but only if serializing 3 packs (same manufacturer, capacity) makes a reliable and safe pack. Also, I have like 5 battery chargers for 2s-6s, but none for 7s+. So I have the capability to charge lots of small packs, but I would have to buy new chargers for 7s+.

It’s really not worth cobbling together a bunch of dissimilar batteries to try and save a few bucks, I guarantee you will get less than half the lifetime of just getting the right pack(s).

Also consider you likely don’t NEED 14s, especially if you are in a budget conscious application, a low quality 14S system isn’t going to net you that many (if any) benefits over a normal 12S.

my next drone is designed around a motor + prop combo with static thrust + power curve using 14s (actually 14s HV, but i think 14s should be OK, e.g. 3.7V nominal vs 3.85V nominal). if i use 12s, my thrust margin will be reduced too much.

by dissimilar do you mean diff manufacturer / capacity? or even same manufacturer / capacity but different cell counts e.g. 6s+4s+4s? (isnt this how the individual pouch cells are aggregated anyways??)

<2 cents>
Combining batteries adds overheads too. There’s more points of failure and more weight.
It’s best to use as few batteries as possible, and avoid serial of possible. Parallel batteries are probably safer.
There’s a good chance your extra thrust in using 14S will be offset by the extra weight and lower current available (with all the extra connections and resistance) , and you’d actually be better off using a good quality 12S battery.
</2 cents>

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Saying 14s will not be better than 12s due to extra weight and resistance is just totally insane. You shouldnt try to “help” people if you dont know what you are talking about. You actually do the opposite if the person actually believes you.

Nah, parallel is not safer. chance of self-discharge. No such issue with serial.

And at the pouch cell level, they are connected in serial the same is if you daisy chain them. There is nothing wrong with doing serial. (same capacity, manufacturer)

some 14s batteries are just 7s in serial in case you didnt know… even this 12s is just 2x6s (PULSE 3300mAh 50C 44.4V 12S LiPo Battery - No Connector)

connector weight is not significant esp higher capacity like 6000 mAh.

if your current usage stays well within C-rating, there arent more “points of failure” (care to elaborate?)

so… no.

i notice you make a lot of posts with lots of content but you should really stop if they are like that.

I offered my view as an opinion, not a hard and fast rule.

Do you think the connectors and wires, and all the connector pins with their milliohms of resistance dont add up?
Sure they are not a lot, but it can all make a measurable difference.
And we’re talking about trying to safely join up batteries of different physical sizes in a vibrating flying machine that relies entirely on electrical power.

Have you tried putting all these different combinations of components into ecalc to see what sort of difference it makes to thrust and flight time?

I totally understand you acquired motors that work best with 14S, but you’re considering budget too. So why not consider 12S (which is a lot more common than 14S) and maybe even go down one size in props - depends how significant the payload is.

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saying 14s will be offset by resistance and weight vs. 12s is totally insane. you have to admit that.

I just offered my thoughts, you go ahead and try it and let us know how it works out.
I will still be curious to know.

:rofl: just why :joy:

It is clear from this thread that you think you know a lot more about these systems than you do. I’m not trying to be rude but your response to someone trying to give you reasonable and measured advice makes it difficult to be completely friendly.

I’m really not sure why it’s so hard for you to believe that a high quality 12S battery is going to actually provide more power and energy than your cobbled together mess of the cheapest crap you can find.

By the way the resistance of a typical connector is The same or usually even greater than adding another cell in series, there is a significant penalty to adding unnecessary ones. There’s lots of other reasons why it’s not a good idea but you don’t seem to be interested in trying to understand them.

At the end of the day it’s your money and your drone just don’t fly over anyone else or their property.

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its just @xfacta. he has been unhelpful in the past and just rambles and meanders needlessly. im actually not sure if he is a passive aggressive troll. i have no issue with anyone else.

and i find it hard to believe a strip of 10 awg wire has more resistance than a pouch cell. but i dont have exact figures (and neither does anyone else apparently).

edit: just think about it. if someone changes the length of battery leads (e.g. cut them in half) are they getting some super upgrade in power delivered? LOL does that make sense? (given impedance / ESC capacitors werent an issue)

resistance figures for thought:

  1. Li-Ion cell (i know we are not talking about them here, but just for some context): internal resistance 20 mOhm

  2. LiPo: consensus seems to be well under 20 mOhm: What are LiPo Internal Resistance "normal" values? - RC Groups

  3. 10 awg (and the “10 awg” wire used in lipos probably have even lower resistance because they can handle more current): 3 mOhm per METER: AWG American Wire Gauge Diameter and Resistance

So that leaves the connectors, which i havent found figures for yet, but are easy enough to measure. it would be shocking though if they were significant compared to internal batt resistance. so where does your opinion come from @mtfunder ?

I’m sure there is quite a bit of variability but…
Some XT60’s sold on Digikey are rated at: 0.55mΩ contact resistance
An XT90 is rated: Contact resistance: 0.3 milliohm