Build a simple 12s pack (2 x 6s/10P) with 21700 cells samsung T40

just a quick thread to build 2 simple packs of 6S/10P to make a nice 12S/10P
cells : samsung 40 T 4000mah 35A in 6S/10 P (25,2V/40 000mah)
enclosure : plastic box IP56 240x190x90mm (perfect fitting)
No BMS for charge et discharge
simple spot welding machine from amazon for eur 50

I printed the cell holder but you can buy it already done

then to secure the cable to the positive and negative

balance cable for 6s (has actually 7 cables) + XT90 with the fuse

solder the cable to side of the battery + balance cable

now a new toy from ISDT battair …a bluetooth device so you can check voltage via bluetooth anytime (never unplug) from android/ios …usd 5 on amazon for 6S device

with the app from ISDT battair you see this on your phone

then you can wrap the battery and put it in the case. yopu leave balance cable inside the case and the psotive & negative out via Gland plug

now regarding charging …the product from ISDT are extremelly good, very reliable and cheap.
I will post later the product I used for charging.
I dont like BMS even when bypassing for discharge , proper RC charger with latest chip are doing a much better job

this ISDT Q8 smart charger is amazing 500w 20A , you can charge the pack in 2,5 hours (from 3,45V to 4,20V) on 10A which is the maximum for these cells![IMG_0247.HEIC|375x500]

but you need an external source for powering the charger from AC current… to be fun and geeky you can use an HP DPS -1200FB 1 A
on 240V you get output of 12V 100A for less then usd 35 (second hand on ebay)

I will send more details of the HP power supply but you can power various lipo chargeurs at once in a very effective way
On 12V you can charge 25v batteries


I think there is a better way to add the main wires. Just in case you looking for some improvements. @kotnascher may enlighten you

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I like the battair :+1: option. Do you know of a siimilar one for 7s. Looks Like battair doesn’t offer a bigger one.

You can even put 2 of those HP PSUs in series if you modifiy the „upper one“. Then you get even more power.

I have not seen 7s ….

hi, not posting often here.
just saw your pack looking good,
any advice for a spot welder? would you recommand the one you used?

Just use this one on Amazon works great for eur 50 …

Here go for the power supply most used by bitcoin miners

I also used the air8 500w 20A 8S from ISDT which is eur 50 on Banggood at the moment and it comes with 2 airbatt Bluetooth (6S and 4s)

So combine with power supply usd 35 you have a serious charger for under usd 100 .

Finish product !
You will need a série cable made of 2 XT90 and 1 QS8 with fuse to hock up to VESC for a 12S 40 Ah

Indeed you can the same for 2x7S or 2x8S these chargers handle both up to 8S

So you divide the risk of your pack in case water come in . I believe you balance the best way possible your pack and control each cell .
Removing the BMS and possible fail and expensive power supply

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thanks for sharing, found another one for about same price

which from reviews seems to be good, though I’m not sure what it can do in terms of nickel thickness and other materials such as copper which seems harder to spot weld,

on 2mm nickel works fine but I find best results on 1.5mm tickness

thanks for details, will probably be fine for my needs

you mean 0,2mm???

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Heyho. The Battery looks good but i think there is a weak point at the end of the main wires. Half of the whole current goes through the nickelstrip between 5th and 6th cell.
For example: If you are using 100A the strip has to carry 50A, which a 0.15mm nickelstrip would not endure very long.


So I should run all the way till end ?
I was doing that at the beginning but got lasy and stopped half way …

Yes for sure !!! My bad


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Do you remove your packs from the plastic enclosures to access the balance plugs, every time you charge? I guess that keeps the plugs safe, provided the plastic case is watertight.

No doubt a hobby charger will balance just fine. One benefit of a BMS is that you don’t have plugs with 13+ pins sitting very close to each other that you need to waterproof/access. The risk of shorting pins and catching fire is a concern.

This business of high powered batteries in a saltwater environment is fraught with challenges :smiley:

yes i have to open the box …4 plastic screws … but it-s water tight so no pain no gain !!!

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