Dewalt Flexvolt 12Ah Li-Ion Battery Repair

[greencardigan]

Hi,

I'm in the process of repairing a Dewalt Flexvolt 12Ah Li-Ion battery pack that had one dead cell.  I've replaced the cell, but found there were a few SMD fuses on the cell sense circuits (on the flex PCB near the dead cell) that appear to be blown.

Can anyone help identify what the fuses are? And if they would be fast or slow blow?  See photo attached. Maybe Littelfuse 0.5A and 1A fuses based on the TF and TH, but I'm not 100% sure. And I don't know why they would be different to each other either.

[AndyC_772]

Why did that cell die?

I wonder if the pack has suffered a failure of the cell balancing circuit, which could explain both a dead cell and the blown fuses. Clearly they're not carrying the full load current of the tool, but maybe they're carrying the cell balancing current? Maybe the fuse(s) died when the cell did, and it became no longer possible to equalise the cell voltages?

[greencardigan]

Not sure why the cell died. Although it seems to be a reasonably common failure mode in these batteries based on my googling. One cells goes completely short and the other cells in that string compensate. You effectively end up with 5 cells paralleled with 4 cells.

The balancing seems to be working. I had them mostly all balanced when I replaced the cell, but after charging they are all really close.

I had to short the two dead fuses to get it to charge.

[bernmc]

Old thread I know, but... what cells are in these 12Ah batteries?

The 9Ah Dewalts have 21700's (samsung or LG), and the 15AH has 18650's (Samsung)

[greencardigan]

Mine had Samsung 40T 21700

[bastl_r]

Old thread I know, but... what cells are in these 12Ah batteries?

The 9Ah Dewalts have 21700's (samsung or LG), and the 15AH has 18650's (Samsung)

Hi
The 9Ah batterys had Sanyo 20700 inside.
The 12Ah 21700 Samsung.
The 15Ah are probably Samsung too.

[coromonadalix]

And  most of the Dewalt batteries  are   

they are NOT totally pushed into the charger contacts pins

they don't balance well

they don't support as we can guess cold temperature,   constructors leave them in their truck  ....

the Flex 60v pack  (have 3 battery group of 5 = 15 batteries) in them, they don't balance well

And you don't leave them  uncharged / depleted  as you may guess


I had access to their innards   from a Dewalt repair friend    loll   not impressed

Some of the battery pack  have an small metal conductor sheet in them , it can act as a fuse,  i simply use an 16- or 14 awg gauge wire  to bypass it,   yeah  no more protection,   i have some of theses "modified pack",  and they take huge beating and stay strong


and yes as the previous thread,  you're right for battery model types

[bastl_r]

I believe, that there is no balancing on the 54V (europe) or 60Va(us) batteries because the charging will allways done by 18V.