OK so my test using this 3S board and a 12.6v input works, but very very slowly, so I dont have the constant current correct.
Ive bitten the bullet and managed to find this:
It seems to be able to do what these 3S balance needs as far as input voltage and current including the smarts to stop charging when needed.
It really is odd that SO MANY balance/charge boards are available yet almost no mechanism for input charge control.
Very strange scenario.
Hi Andrew
You do realise that device is for 1 cell, 4.2V don’t you. Not 12.6.
That is set by the 12.6V source supply.
If you have one of the chargers such as like the couple that Core stock the current limit as well as everything else like number of cells, cell type and everything else is set up with the parameters that have to be entered into the charger prior to operation. I think most of these BMS devices look after the balancing system. The complete chargers mentioned above have the ability to monitor the status of individual cells or the bank of cells in parallel at the 3.7V level.
Cheers Bob
Yeah I linked the wrong one, good pick up.
Hi Andrew
Looks like this will supply the 12.6V @ 1A but I think you will still need a BMS for cell balancing.
Cheers Bob
Yep, using the one from this thread.
@Robert93820 and anyone else interested, that 12.6v LiPo charger that I bought off ebay did the trick wonderfully.
Using the balance module from Core:
and the charger:
My simple 3S 18650 pack now charges to a ‘full’ 12.6v.
On a side note, I am absolutely gob-smacked at the hardyness of 18650 cells.
About 13 years ago at work IT did a laptop refresh and they e-wasted hundreds of laptops.
With permission, I was able to rescue about 35 of the battery packs from these laptops, and as a result have had a stock of hundreds of 18650 cells.
I just shucked the cells out of a pack yesterday, that hasnt been in a laptop for 13 years, and was about 5-6 years old at that time, so these are roughly 20 year old cells, not charged or used in 13 years.
Straight out of the pack and they were ALL 3.99v exactly, totally balanced.
I put them on my good 18650 individual cell charger and they ALL came right back to 4.188v on the nose.
yes they are off spec for 4.2v cells, but for free they are really close and working perfectly.
Anyway reason for the update was to say that that module from Core works a treat to build 3S packs as long as you have a compatible ‘proper’ charger like the one that I linked.
@Graham maybe you can look at finding a similar charger then you can sell them as complete kit.
Hi Andrew
Good that is sorted.
4.188V compared to 4.2V. That is 0.0029%. Well within the measurement spec of your DMM.
Unless of course you have a really really accurate Lab meter and measured at exactly 25ºC.
Cheers Bob
hahahha, you know the answer to that 
My calculator gives 0.285% which is actually within the accuracy spec for a good workshop multimeter (depending on the voltage range).
Hi All
OOPS. Forgot to move the decimal point. Senile decay (my excuse anyway). Should have been 0.29%. The discrepancy between 0.29 and 0.285 is when I divided 4.2 bu 4.188 I have my calculator set to display 4 decimal places (it is capable of displaying 16 (in 2 banks of 8)) so it read 1.0029. Thanks for the correction Jeff.
Cheers Bob
Hi, just a quick question about these BMS boards. Can they be used for 1 or two cells only - ie 1S or 2S? And if used for two cells, can you leave B+ to B2 open or should it be shorted? A schematic would be great.
Does anyone know if the BMS can use two cells, or do all three have to be used. Was thinking that if you drop a cell, it would decrease the voltage. Not sure if that would confuse the BMS.
Hi @Aaron268548, Welcome to the Forums!!!
The 3S 18650 BMS Module we currently have has a 8254A battery protection chip controlling it.
Reading the datasheet for it, the chip can only be switched between 3 and 4 cell operation.
As such I wouldn’t recommended trying to use it with 2 cells.
I suspect it will see there’s no voltage across cell 3 and go into an over discharge protection mode.
Thanks for information, and the datasheet, yet I see what you mean. Thanks for getting in contact.
Hey all. Relative noob here. Need help!
Can’t figure out what I’m doing wrong. I have the bms wired up to 3 18650 in series. Yet I get 0v on the output.
Each cell is full charged, I get 4.18v per cell.
Measuring across B+ and B- terminal on the bms I get 12.55v
B+ to B2 : 4.18v
B+ to : 8.36v
B+ to B-: 12.55v
But across P+ and P-, I get 0v
Any ideas? I must be doing something silly. I have tried two bms boards in case I cooked one somehow. Same result both times.
Have you tried charging the cells from the P terminals? Sometimes a BMS needs a kick start from the charging port in order to wake up from protect or sleep mode.
Hi Chris,
Give Jeff’s suggestion a go! There are a handful of reasons a BMS could go into protect/sleep mode so knowing how to wake them up is important. Here’s an article with some more info.
It worked! Thanks guys!
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