SOLVED: High diff. voltage of 2 adjacent cells at absorption -> defective active balancer

[juepi]

Hi Folks,



Guess when i've connected my shiny new balancer... ?

Case closed imho ?

Thanks again to everyone who assisted me in this case!

Have a sunny weekend,

Juergen

P.S.: Updated thread topic to be hopefully more helpful for the future

 

[740GLE]

Btw what’s your reasoning for sticking your balance/sense leads on top of those nuts?

IMO they should be right on top of the bus bars. It’s prob not any major issue I’m more curious at your thinking vs my own.

 

[740GLE]

View attachment 152981

Here you go, should be fine imho.
There is another reason which makes a defective balancer more plausible: since the active balancer was connected, it was never activated (which means the 2 "RUN" pins shorted; that extra wire is not connected in the picture), but when i got my first full charge, cells 2 and 3 already were massively unbalanced as it seems.
Will get my new balancer on saturday, then i can tell for sure what's wrong (hopefully!).

yours,
Juergen

Also what the heck is connecting + and - terminals on cell 4?

Something plastic I hope?!?!? ?

 

[juepi]

Btw what’s your reasoning for sticking your balance/sense leads on top of those nuts?

IMO they should be right on top of the bus bars. It’s prob not any major issue I’m more curious at your thinking vs my own.

The main reasons were:
a.) easier to handle (assemble / disassemble) when the busbars have their own attachment
b.) fom electrical point of view it will imho not make any difference due to neglectable currents (practically nothing to BMS and i've measured 1A to the balancer when balancing the far-off cells 2 and 3 correctly after attaching the new balancer), thus neglectable voltage drop between busbar and balancer/BMS wires
c.) i've avoided stainless steel and used galvanized grub screws / nuts (lower resistance)

yours,
Juergen

 

[juepi]

Also what the heck is connecting + and - terminals on cell 4?

Something plastic I hope?!?!? ?

yeees, something plastic, else i'd have some major other issues i assume
It's a mounting for the Daly BMS temperature sensor, which "connects" to the battery valve of cell 4.

yours,
Juergen

 

[HRTKD]

c.) i've avoided stainless steel and used galvanized grub screws / nuts (lower resistance)

I'm no expert on this but I question using galvanized steel in contact with aluminum.

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However, the stud on the cell shouldn't be the path of the electricity. The path should be from the cell terminal surface to the cable lug or bus bar. Therefore, it's probably more important to avoid any chance of corrosion that it is to worry about resistance.

Reiterating what 740GLE said, the balance leads should be right on top of the bus bar, not on top of a nut.

The threaded rods should have a sleeve of non-conducting material on them. The cells can have current running through the case. You don't want the threaded rods to make a connection.

 

[juepi]

I'm no expert on this but I question using galvanized steel in contact with aluminum.

Absolutely true, that's why you want to use special terminal grease for alloy getting in touch with steel (or copper) to avoid contact corrosion. I've used WAGO 249-130 for everything getting in contact with my battery terminals.

However, the stud on the cell shouldn't be the path of the electricity. The path should be from the cell terminal surface to the cable lug or bus bar. Therefore, it's probably more important to avoid any chance of corrosion that it is to worry about resistance.

Agreed

Reiterating what 740GLE said, the balance leads should be right on top of the bus bar, not on top of a nut.

That is of course the optimal solution. However, as explained, i doubt that it will make a practical difference for balancing currents of ~1A.

The threaded rods should have a sleeve of non-conducting material on them. The cells can have current running through the case. You don't want the threaded rods to make a connection.

Took a while, now i (hopefully) understand what you mean
As my whole battery is in a (closed) box, the threaded rods are not causing a high risk of causing short circuits, but in terms of security i agree that in general it is a good idea to cover all of the "battery top area" with some sort of acrylic glass or equal.

yours,
Juergen