vh2q wrote:Well fast fforward a month, I got set up with hobdrive and took a look at the ECU data. Getting two error codes P1A4B (cell voltage abnormal) and P1A2F (cell error). Charged car up to 3 bars, which is all it will take, and read. voltages. All around 4.1V except one cell is 3.79V. TrIed to actuate smoothing from hodrive but not clear to me. it did anything. What am I missing here? Is there something else I should look at or reset using hodrive? I still don't know whether the problem is the gauge (ie showing 3 bars when it's actually fully charged) or the charge cycle cutting out too soon, I have run it down to the tortoise symbol a couple of times thinking that may reset the BMU but it doesn't seem to make much difference. Car was fine until I let it sit without the accessory battery for about a year.
The cell smoothing option in Hobdrive is supposed to activate the cell balancers manually in the battery pack however I did not have any luck getting this to work when I did a cell swap and had an imbalance to correct. (To be fair my dealer diagnostic tool was also unable to do this)
Keep this in mind though - the cell balance resistors only draw 100mA, this is a tiny bleed current, so it will take a long time (dozens to hundreds of hours) to make any real dent on this level of imbalance.
When I did a cell swap I ended up with a 50mV imbalance at full charge so the cells I replaced were only reaching 4.05 volts when the others were at 4.1 volts. That small 50mV error took approximately 40 charge/discharge cycles over about 6 weeks of daily driving and use to equalise, however the car still worked normally during this period.
However your imbalance is 290mV - this is massive, and if we assume for the moment the cell is OK but it is only a SoC imbalance it would take approximately 240 charge/discharge cycles for the cell balancers to correct.
I think it's very unlikely that it is just a SoC imbalance, and that you almost certainly have a faulty cell, although a faulty LTC chip on the CMU board is a possibility.
Either way the pack will need removing from the car and the module containing the cell carefully removed so the cell voltage can be measured - if the voltage is indeed 3.79 volts the cell is faulty, if the voltage measures the same as the others the LTC chip on the CMU board for the module is faulty.
If you do perform a cell swap then to avoid the same mistake I made I would recommend you fully charge the pack in the car until all the other cells reach 4.1 volts, and make sure the replacement cell is fully charged to 4.1 volts before fitting it.
If you go ahead with a cell swap good luck and be careful as there is a risk of electrocution if you are not very careful and competant, and feel free to ask questions here. I took quite a few pictures of my cell swap job even though I never got around to posting them here.