OEM LiPo curosity got the best of me

[TeamMishap]

I've been using the OEM 11.V 1800 mAh lipo from my ParkFlyer Edge540 for my Trex 450XL.

I've been using the crappy wall wart charger for it, which from what I've seen is about as reliable as a gas station condom.

So I've ordered a decent lipo battery and a Cellpro 4S so I don't have to worry about charring the inside of the ammo box I use to charge batteries in.

Curiosity got the best of me. I couldn't help it. I know it's dangerous and reckless, but with Nomex gloves on, a sharp plastic cutting implement, and nothing nearby to catch fire but myself, I excised the shrink wrap off the top of the OEM battery to assess the prospects of putting a tap on it that will work with the new charger coming.

Inside, it looks like there are 6 cells instead of 3. It's got 12 freakin' tabs on the top. Can there be 6 1.85v cells in this thing? That doesn't make sense.

Any guesses, links to explanations, etc?

Thanks all

[eurylokhos]

If there's 6 cells in there, then it's made of 6 900mah cells , so it's actually a 3s2p1800. Nothing magical, just the manufacturer buying cheap stuff and coming up with a way to make it work.

[TeamMishap]

Geez, that thought never even crossed my mind. Simple math. I feel so stupid. Makes perfect sense! Thanks!

[eurylokhos]

No need to feel stupid, sometimes you just need another person to point out what you overlooked. Glad I could help.

[TeamMishap]

Yeah, if 900 mAH are more than half as cheap as 1800 mAHs, then I guess the 3S2P config makes sense for a cheapo pack.

[TeamMishap]

I think I figured out the electron flow on this stupid thing... assuming this is a 3S2P with 900 mAH cells as Eurylokhos suggests.

I measured the voltage across all points. Measuring from the positive points on cells 5 and 6, these are the approx voltages I got.

Cell stack:

cell 1 + - 11.1v
cell 2 + - 11.1v
cell 3 + - 7.4v
cell 4 + - 7.4v
cell 5 - + 3.7v
cell 6 - + 3.7v


It's looking like cells are parallelly paired 1-2, 3-4, 5-6. Serial connections, I'm guessing, are made between (cell 5 negative and cell 4 positive) and (cell 3 negative and cell 2 positive).

I'm flummoxed on the power leads though. It appears the negative originates on the circuit board between the negatives on cells 1 and 2. The positive between the negatives on cells 3 and 4.

My assumption is the negative lead marries up with the negative poles on cells 1 and 2 and the positive lead marries somehow with the positive poles on cells 5 and 6.

I'm going to try to put a 3S balancing tap on it with negative terminal at cell 1 (-). Second balancing lead will go on cell 2 (+). Third balancing lead will go on cell 4 (+). And positive power terminal on cell 6 (+). This is all conjecture, but I think this will isolate each 3.7v cell pair.

Failing this...which it looks very likely it will...anyone know if it's possible to hook a battery without a balancing tap on it up to the Cellpro 4S with only a Dean's connector?

[TeamMishap]

Well, I soldered some taps on Frankencell today. Cellpro 4S charger comes tomorrow. Either I did it right or blows up. All the voltages are reading properly, so that tickles me and gives me hope it won't explode. (laughs)

[TeamMishap]

Cellpro 4S is charging Frankencell. No explosions yet.

The cheesy wall wart charger was pretty useless. The pack is all kinds of out of balance! I think Cellpro is going to qualify for another battery save, albeit on a cheap pack.