Sandrosan wrote:Hello DBMandrake and hello to all others in this very interesting forum,
My name is Sandro from Milan, Italy. Sorry for my poor English. I own a C zero and I have 2 friends with C zero too.
My second hand C zero of 2011, has only around 24000 km, 14k of them driven by me since I bought it in Oct 2017.
I can drive my car for approx 90 km in winter and 110 km in summer.
I use Canion with ODB Link LX and in case of SoC around 10%, I have 2 weak cells with up to 100 /110mV of difference with the highest cells. My pack has some 36 / 38 Ah according to Canion.
38Ah is not that bad for a 9 year old car. My car at 6 years old and 28k miles was only 39.9Ah.
As with my 2 friends we bought an i-Miev from wrecking, we have dismantled it all and took all parts as spare parts for our C zeros, we just throw away the chassis..... (you can image how happy is my wife with so many car parts in my cellar
Therefore we have the battery pack too (by the way, I confirm there is Hall sensor for DC current measurement inside the batt. pack and I think to adjust its output analogue signal would not be too difficult in case we need to change the all cells with much higher capacity...).
I tested all the 88 cells by two different milliohmeters and I can select the best ones based on the internal resistance (this varies from 1.49 to 1.73 milliohm with one milliohmmeter, with the other one 1.75 to 1.98 milliohm).
However a better device for capacity cell measurement would be opportune I think....
Measuring the cell internal resistance with a milliohmeter would be very difficult I think, as the current is too low for the low resistance. Unless you use a securely bolted and soldered terminal, the resistance of alligator clips will be much higher.
1.5 - 2 milliohms sounds perfectly normal, and will of course vary with temperature.
Can I ask you the following questions?
-If I understood well, you replaced 4 cells in your car last Nov 2019. But you did not charge them like the other cells. Now few months passed, so I guess the charge level of the 4 cells should be aligned to the rest of the pack. Or not?
Yes. It took about 2 months of normal driving for the cells to finally reach perfect balance at 100%. The mistake I made was to swap the cells when the pack (and replacement cells) were voltage matched at about 20% SoC.
The replacement cells have more capacity than any other cells in the pack as a result they need more charging to get from 20% to 100%, so by the time other cells were at 100% the replacements were only at about 95% and were about 50mV lower than the rest.
This took dozens of charge cycles to rectify as the error was around 2Ah and the balancers can only draw about 100mA during the latter part of the charge cycle, however they did eventually come into perfect balance.
In hindsight I think a cell swap into a working pack should be done with all cells at 100% SoC - by charging the pack in the car, and also charging the replacement cells on a Lithium Ion charger to exactly 4.1 volts.
One reason I did not do this was to compare cell voltages with those reported in Canion to help identify cells in case there was an error in the cell layout chart I used, however the chart turned out to be 100% correct.
How is the range now comparing before the swap?
No real change unfortunately. Before the swap it was at 33.0Ah, after the swap and a battery calibration it went up to 34.0Ah however in the months since then it has slowly ticked back down to 32.5Ah, so I am worse off than when I did the cell swap.
There are other cells that are also quite weak and it would require the replacement of many more cells to make a meaningful difference. In short it is not worth doing.
-My weak cells are 53 and 57 according to Canion. How can I located them in the pack apart measuring the voltage cell? Is there any other way to locate them?
I see someone has already provided you a link to the cell layout.
However after my own experience and given that you still have a usable capacity of 38Ah from a 9 year old car I would recommend against performing a cell swap - you will almost certainly not achieve any useful or permanent improvement in capacity after a lot of hard work and expense.
In hindsight the swap I did whilst technically interesting and challenging was not worth the time and effort, and I have plans to sell the car and get something with a good bit more range, probably a Leaf 30kWh.
What you are seeing is not two faulty cells, just two cells that are nearing the end of their lives a little bit before other cells, but other cells will soon follow, so you would be forever trying to replace cells to keep up.