iMax B6 only seeing 5 of 6 cells in a Li-ion pack
Hopefully this is the right place for a question like this, if not I would really appreciate being pointed in the right direction because I'm ready to tear my hair out at this point.
For background - I have a Bissell stick vacuum that stopped working a few years ago. I assumed it was the batteries, so I took it apart and found that the unit is powered by 6 INR18650 cells that are not sealed, just welded with nickel strips and then soldered to the main board. I rebuilt the pack with new batteries and it worked... for about 10 minutes. I hadn't though about needing to make sure they were topped off or balanced and came to later find that the vac is able to sense an imbalance in the pack, but cannot recharge it - it just stops working.
To resolve it I bought an iMAX B6 LiPo Balance Charger on Amazon, soldered some leads to the positive and negative terminals, and connected up a 7 pin JST-XH connector for the balance charger port.
The issue I have is that when I try to start the Balance process on the charger it reports backR: 5SER S: 6SER
Indicating it only sees 5 of the 6 cells in the pack.
I have done everything I can think of to sort this out:
- Confirmed the JST pins are in the correct order.
- Tested voltage from each pin (see below).
- Confirmed continuity from BAT- to each pin.
- Checked resistance from the JST connector to the battery terminal.
Here is a logical diagram of the cells with the voltages measured:
BAT+ -----------------------------------●
│
Pin 1 (20.28 V) ---------------------------------●
│ C │
│ e │
│ l │ (3.37 V)
│ l │
│ 6 │
Pin 2 (16.91 V) ---------------------------------●
│ C │
│ e │
│ l │ (3.41 V)
│ l │
│ 5 │
Pin 3 (13.50 V) ---------------------------------●
│ C │
│ e │
│ l │ (3.39 V)
│ l │
│ 4 │
Pin 4 (10.11 V) ---------------------------------●
│ C │
│ e │
│ l │ (3.40 V)
│ l │
│ 3 │
Pin 5 (6.71 V) ----------------------------------●
│ C │
│ e │
│ l │ (3.42 V)
│ l │
│ 2 │
Pin 6 (3.29 V) ----------------------------------●
│ C │
│ e │
│ l │ (3.29 V)
│ l │
│ 1 │
Pin 7 (0.0 V) -----------------------------------●
│
(MM COM) BAT- ----------------------------------●
I will readily admit that I have gotten myself confused and turned around when it comes to pin order. From what I am seeing in the instructions pin 1 (far right when looking at the connector end, with the lock on the top) is the positive end of the pack. That said, if I reverse the order I still get 5SER from the charger, it only tells me that the polarity is reversed it I swap the output ports.
From the measurements though, you can see there is some imbalance in the pack, but I get clean voltage measurements in the proper order from the pins, so I don't think its a bad connection. I also checked resistance from each of the pins to their respective battery terminal and none of them read above .3 ohms. I even tested on a 2nd B6 unit and it also reports 5SER for the pack, so I don't believe its a faulty charger.
I did see a comment somewhere that the B6 only supports a 6 cell pack in certain modes, but I cannot validate that comment anywhere in the instructions or online, so I don't know if I believe that claim.
At this point I'm all out of ideas, outside of asking Reddit I'm thinking I have 2 options:
- Tear the pack down and charge each cell individually - but that's a PitA because they're all spot welded together.
- Find a hobby or electronics shop that I can take it to and see if they can tell what I did wrong.
So, I would really appreciate any expert guidance you all could provide!