16s BMS with 16 balance wires question...

[rg12]

Hey Dudes,

I have a 16s pack that I built from brand new Samsung 26F cells and when fully charged it was around 64.5v (almost one cell less than normal (voltage wise).

I just measured the balance wires and something is very strange...

Usually a 16s BMS has 17 balance wires, and mine has 16 which means that the first cell in the pack is not connected at the negative side (that's how it's shown in the diagram that came with the BMS. logicallt it can either be no negative for the first cell or no positive for the last cell, but I followed the diagram and went with the first option).

So if I measure the overall voltage through the balance connector (one probe in the far left and one probe in the far right) then I get a 60.7v (fully charged) because it measures cells 2-16 without cell number 1.

That's why the charger is charging up to 64ish volts instead of all the way I guess...
What do I do? is that normal?

 

[dogman dan]

The first negative wire is not on the balance plug. its on the main negative wire of the pack. sometimes this is numbered wire 0 on a diagram. one neg, 16 positives.

 

[rg12]

Yes, that's what I thought, why put a first wire when you can have it preconnected inside the BMS to the negative already.
So I soldered everything correctly...why the hell does it stop charging at 64.5v? charger's voltage is 66.8v
It doesn't balance or anything, just turns green and does nothing.

 

[TristanP]

You already opened another topic in regards to the same issues, with the same pack. In that topic you also mentioned your charger is giving an output of 66.8V and 0A.

Personally I would expect your BMS needs a minimum input voltage of 67V. If that's the case it's nothing but logical your pack doesn't get charged (further) and you measure 0A with your multimeter. Not saying the charger is the problem in this case though.

It could be helpful if you could provide us with information in regards to the BMS and charger used, as well as use your multimeter to check if your cells are properly balanced.

 

[rg12]

The no current thing is not a sure thing at all since I couldn't get it to charge at all even when the pack was 50% charged when I connected the charger in series with the multimeter.

Right now I think I'm on to something, all cells are 4.03-4.04v and cell number 15 is 4.17, so I think that maybe it halted the charge until this high cell bleeds super slowly to a voltage that is closer to the rest of the cells in order to proceed with the charge, so since the BMS bleeds in a speed that can make me age then I have connected it to a small light bulb to drain it a bit faster (still took a few hours to drop from 4.17v to 4.11v) and will try to charge then and update here.

 

[rg12]

SOLVED!
Drained with a bulb the voltage of cell number 15 which was 4.17v while all others were 4.04v and it's now charging and almost full!