Help building 6S2P balanced Li-Ion battery pack

Hi, I’ve been redirected here from quadcopterforum.com , I’d like to build a battery pack with these specs:

  • 22.2V
  • at least 5000mAh capacity
  • at least 30A constant discharge current
  • XT60 plug for charge/discharge
  • JST plug for balance
  • lightweight

LG 18650 HG2 in 6S2P configuration should meet them:

  • 22.2V
  • 6000mAh capacity
  • 40A constant discharge current (safer)
  • about 600g weight

the battery pack is for a quadcopter, my question are:

  • 1 ) do you know better quality/price Li-Ion cells in 18650 or other standards?
  • 2 ) I found cheap HG2 cells on AliExpress which suppliers told me they are not genuine but with same specs, can I trust them or where do you advice me to buy them?
  • 3 ) can you show me how to wire the 6S2P pack with XT60 and JST plugs for charge/discharge/balance? Thanks
  1. Samsung 30qs

  2. do not trust them. use nkon, imrbatteries or other reputable companies.

  3. I’m not the one to look for help on that, but there has been lots posted about it. The search button can help with that though

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The batterys you want to get are probably not good if there fakes.

Get something like samsung 30q from Nkon https://eu.nkon.nl/rechargeable/18650-size/samsung-inr-18650-30q-3000mah.html

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do you mean Samsung 30Q?

I know it but is only 15A and I’d be a bit on the edge.

I can’t find datasheet for Samsung 30QS.

the reason because I was looking on AliExpress is because I need cells with presoldered nickel strips, because I don’t have a spot welder.

I didn’t find wiring diagram for 6S2P, I’m not sure how to connect balance leads

what about 21700 cells?

Out of interest, is there any reason why you’re going for cylindrical cells instead of lipo pouch cells? Lipos are usually a lot more power dense (higher discharge rate for a given capacity) and therefore better suited for weight critical applications like RC aircraft.

LiIons are lighter so I can build a 6S2P pack with 30% more capacity than a 6S1P Lipo with about the same weight, also they should have a wider workable voltage range. the cons is that they have lower C rating, but in low amperage consumption endurance quadcopters like mine 18650 cells are widely used.

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They dont have the same specs, avoid

30Q rated safe at 20a continous, look up mooch’s test on them

Google “30q spec sheet”

It’ll depend on bms u choose, but shouldn’t be a problem, come back here once u decide on a bms

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Nkon.nl or Nkon.ru are amazing, you can get the cells there, if you don’t have any spot welder you can have a look at N.E.S.E modules, they are hella easy to assemble and to check your battery health, BMS would be a good choice bestech

Don’t buy any skateboard battery from the 'baba

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good to know , I read here https://www.18650batterystore.com/Samsung-18650-p/samsung-30q.htm they were rated 15A.

he wrote 30QS

I wont use a BMS, I’d like to connect a JST plug for balance charging using my iMAX B6 Mini, but I don’t know how.

@Davide are you italian? I don’t like these kits like N.E.S.E, VRUZEND etc because are espensive and heavier

I’d rather buy cells with presoldered nickel terminals

1

and insert 3 of them in each arm like in this video

otherwise what about combining 4 of these case holders? 2

regarding chinese cells (since I dind’t find cells with presoldered nickel terminals elsewhere) I’d ask to sellers and if they guarantee me the specs, I’d give it a chance, in worst case I’d ask to refund.

even for genuine LiPo batteries they recommend to never leave them in charge unattended

Sorry, I was meaning multiple and forgot the apostrophe. 30q’s

np I had imagined it but in doubt I asked :wink:

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Thats plural, S, no such thing as 30qs

Yeah mate I am, no one is perfect​:rofl::rofl: don’t know anything about those cell olders, NESE modules are pretty much plug and play and very strong, anyway when I bought the cells from Nkon I saw they can add solder tags if needed

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even on nkon 30Q cells are 15A rated, anyway according to this video (imho trustable) Liito-Kala chinese cells should be good enough, so for half price I’ll give them a chance.

anyone can show me a diagram of how the wiring should be in a 6S2P with XT60 charge/discharge and JST balance plugs? if you can, for semplicity, draw it on this image:

Senza-titolo-1

on soldered tags, soldering iron and 16AWG silicone wire are ok ? any advice on how to do it?

6S2P_layout

Others can check me but pretty sure this is correct. Basically putting 2 cells in parallel 6 times then wire those groups of 2P into series to make the 6S, each balance lead goes between the groups of cells (measuring from ground through each balance lead you should see the voltages shown if the cells are all fully charged) Simply check a known good LiPo you have with a balance lead on it for which side is 0V and to see the step by step of voltage from each pin in the plug just keep black of multimeter on first pin and go one pin to the next with red probe (in DC voltage measuring mode).

In the arrangement you’ve shown I suppose you could pair up the ones in the center of the quad to make 2P groups so would have 2 of those between the 4 cells that meet at center then put the two “extra” ones in the arms as a p-group but having them lined up end to end is putting them in series they have to be side by side or have wires run to effectively have negative to negative and positive to positive (parallel)

Also to note the lines going to the balance port (imagine bottom lines going out of page go to balance connector), those balance lines look like they are connected to battery negative but really anywhere between the cells in series is effectively the same voltage. So far right most thick red line is same voltage as the black line to it’s left (they are just connected with a wire/nickel strip). Regarding gauge of wire with short runs from what I gather it shouldn’t make a large difference but again multimeter is the best way to know for sure measure ohms and can calculate voltage drop given some assumed load/current (search for voltage drop calculators quite a few out there just want DC voltage).

wouldn’t be simpler to make 4 3S packs (one for each arm), then pair them in 2 6S, and finally in a 6S2P ?
or is it not possible beacause of balance leads?
looks like they did that in this video (first image at 0:05)

is there an order in which to proceed when soldering to avoid damages?

You could do that the problem would be extra long connections between the cells in parallel means the resistance on that connection will be higher and less even (shorter the material between two things lower the resistance so closer they are together and closer the discharge connection is to the middle of the wire between two cells in parallel, that said the actual connection points between the metal tabs and cells will probably effect resistance more than being a bit off on lengths of anything).

Regarding avoiding damage to things, the main things are to not get the cells too hot while connecting things and to be sure the voltage of all the cells is matching (within .1V but closer they are the better, when you hook two cells in parallel the voltage will drain from the higher charged one to the lower charged one, the rate of charge/current will depend on how far the voltage is off from one cell to the next, when hooked in series no current will flow until the circuit is completed but you still want the voltage of all the cells in series to be roughly the same (balanced) for the sake of not overdischarging or overcharging any of the cells.

you are right, in the meantime I understood, now I’m preparing the final schema for confirm
I’ll buy all the cells at once and I think sellers charge them before shipping but because of long delivery time they could be different in charge when they arrive, so maybe I’d better buy a 18650 charger too but I think they can only charge to max voltage right?
can I solder balance leads on any of the to the 2P cells?
another question, should I isolate the cells from the frame (aluminium) and each other? and how?

Yah if I were to attempt this would probably just center all the batteries having the weight further out is just going to make it harder to pitch/roll and for the quad to balance itself I’d guess and not sure what benefit you’d get spreading the cells out.