Lipo battery pack build question

Atxraider

10 µW
Joined
May 17, 2022
Messages
5
https://electric-skateboard.builders/t/lipo-battery-pack-build/118011

Sorry for being lazy and not wanting to re-type my question and instead put a link to it.

Thank you in advance

(moderator edit: copied and pasted text from linked page below in case link goes away...pictures showing damaged and swollen packs at link not included)

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Lipo battery pack build
ESK8 Electronics
battery
Atxraider May 11, 2022, 5:48am #1

I have a Trampa Mountainboard I’ve had for awhile that has dual Max6 ESCs and was powered by dual 4S Turnigy Graphenes 10.0 (10,000mah) that were connected in series to give me 8S. Well, one of the batteries recently started only showing 2 cells instead 4 when charging and puffed up. I haven’t been able to recover it.
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But still have one of the Turnigy Graphene 4S batteries working.

The other day I went and picked up 4 new lipos along w a parallel charging board.
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I connected these 4 as follows: 2 sets of 2 batteries in parallel that are then connected in series. Which gives me a comparable battery at 8S 10,400mah.

The question I have is it possible/safe to connect the remaining Turnigy Graphene 4S lipo in series w the 4 new lipo batteries to make it 12S? The reason for me wanting to do this, besides the added range and power, is bc I’m wanting to switch over my ESC to a Focbox Unity. Thanks for your help in advance.
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LeonCamero May 11, 2022, 5:54am #2

The question I have is it possible/safe to connect the remaining Turnigy Graphene 4S lipo in series w the 4 new lipo batteries to make it 12S?

If it was up to me, I wouldn’t. Different batteries and possibly different cycles and chemistry. But I’m not an battery expert, especially when it comes to lipo and different c rating (which I assume is why i wouldn’t do it). Maybe someone else who uses lipos can answer.

Edit: found it. No. Do not do it. It has to be the same in c-rating, age and company it came from. Yes, they use different chemistry.
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Atxraider May 11, 2022, 7:26am #3

Okay, that’s what I was afraid of. Thanks for your response.
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Atxraider May 11, 2022, 8:01am #4

Any idea how I would wire a BMS to the 4 - 4S batteries that are making up the 8S2P pack? Would I use all 4 sets of the balance leads or just pick one balance lead from each parallel group?
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kavic5150 May 11, 2022, 12:02pm #5

Lipos with and wthout graphene can be mixed but they have slightly different levels of performance. There is a chance that one pack would get depleted before the other one leaving it to do almost double duty. Its typically not good to mix batteries in series or parallel unless they have matching C ratings and a similar cycle count.

I recommend not using Lipo batteries at all for an Esk8 because they are not designed for it and can be easily damaged. Those soft sided packs are designed for aircraft and cannot handle all the bouncing and jarring around they would see on a skateboard. Which is possibly why one of them puffed.

The other reasons they puff is too high of a charge or discharge rate which is unlikely since the aircraft and heli guys sometimes draw a lot more amps from them than a skateboard typically would.

Leaving Lipos in direct sunlight is also a no-no especially on very hot days. Even leaving them inside of a car on a hot day is dangerous and can puff them.

At the very least make sure those lipos are well padded and isolated from vibrations as much as possible and use a light colored housing for them so they dont bake in the sun.

I’m fairly new to Esk8 but I’ve been in the Rc hobby for over 10 years.
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LeonCamero May 11, 2022, 12:17pm #6

There should be a tutorial on this site or the other about it. I normally use li-ion.
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You know there’s a copy and paste function..?

Your 4 cells are already suspect so beware of something like this: https://youtu.be/_5E2-qmcLHk

I would throw them.. not worth it, even if they can be used with caution if treated like a separate battery.
 
One of my 4S Graphenes is still good, while the other is only reading 2 cells out of the pack. I’m talking about using the 4S Graphene pack that is still good. Is it possible to connect it in series to the other kind of 4S packs?
 
The old and the new packs have different capacity and voltage drop - the old pack will drop more, and these cells will be stressed more.

Let’s say the cells are hooked up in series and a bms is used to ensure that all cells stay within safe limits. Still this battery will (likely) not be balanced enough after each use so it will need separate charging and balancing. This since the balancing currents of most bms are designed to take care of minor cell differences, not actual capacity difference or cell chemistry difference.

It’s a lot of hassle to save a few bucks and the risk taken is fire, damages and you/your loved ones/other people killed.
 
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