Which cell loses capacity fastest? Which retains it best?

[RegGuheert]

Anyway, here's what my pack looks like this morning after charging to 80%. Just eyeballing it, relative balance appears to be similar to the pics from VLBW.

Agreed. Cell-28 may prove to be the weakest one in the pack.

Not going to charge to 100% since it's supposed to be a scorcher today will be interesting to see how hot the pack gets. The pack didn't seem to cool off much from last night. Garage temps a steady ~70F with an overnight low of 59F.

It might be interesting to see these voltages again after a few hours when the pack is in an isothermal condition, just to see if it makes any difference.

 

[timhebb]

In my spare time at the end of the month I rotate my cells for longer life. No sense in not dropping the pack once in while and spending a full day rotating modules. I worked on an spreadsheet to track the rotations and a graph on the time spend VS percent capacity gained. I divided that by the number of days in the year multiplied by how I would rather do something else and came up with time spent doing other things would be a better choice. Next up I'm going to plot the wear of my wiper blades from end to end and measure the wear deviations. I may put this on Google Docs.

+1.0406459754...

No one else seems to appreciate your very dry humor here, so I just thought it shouldn't go unrecognized. Very funny.

 

[toasty]

http://www.ebay.com/itm/Auto-Car-V1-4-ELM327-OBDII-OBD2-Bluetooth-Diagnostic-/300515166540" onclick="window.open(this.href);return false;

is this it?

 

[RegGuheert]

http://www.ebay.com/itm/Auto-Car-V1-4-ELM327-OBDII-OBD2-Bluetooth-Diagnostic-/300515166540

is this it?

There is a smaller one in a clear blue case which I wanted to get, but I'm also not sure if some are fakes which will not work well. Anyone have some guidance?

 

[FairwoodRed]

I bought this one and it works great. It is the smallest of the three versions: link

My coworker bought this one and it also works great. It is slightly bigger than mine: link

I ordered a second one and the rock bottom price I could find: I intend to cut it open and see if I can modify it to read the EV CAN buss:link

This one is the largest of the three versions. It is supposed to have screws under the label that would make is a lot easier to open and modify. Since it is larger, some people may have trouble with it brushing against their leg: link

 

[LEAFer]

http://www.ebay.com/itm/Auto-Car-V1-4-ELM327-OBDII-OBD2-Bluetooth-Diagnostic-/300515166540

is this it?

Works. Arrived in three days. $11.79 incl. shipping.

 

[DaveEV]

So I know some of you thought that my earlier images showing low voltage of CP 24 was evidence that it was "weak" compared to the rest, but I was not yet convinced as it is just as likely that the particular CP is just undercharged in comparison.

So I charged to 100% Saturday and then drove about 5 miles past LBW (LBW came on at an indicated 23.9% SOC, BTW).

My thoughts:

1. Overall shape of both charts is basically the same.
2. max/min difference is basically the same with the min CP staying the same and the max CP coming from one of the highest in both.
3. Mostly charging to 80% and top balancing doesn't seem to be effective at keeping the pack optimally balanced when there is a small number of CPs that are undercharged.
4. I wonder how much range I am losing because of the balance?

Some of you guys have very good pack balance with min/max CP differences less than 20 mV. My pack is typically around 30-35 mV. Would be interesting to see what typical CP differences are with varying charging habits.

 

[FairwoodRed]

I was at my local EV meeting and scanned all the Leaf's I could I posted screenshots here

Most of them have Cell Pair Voltage spreads in the mid-teens. Looks to me like you would benefit from a week of disabling your charing timers.

My personal Leaf screenshots can be found here for comparison. I hit a low of 85.81% CAP this weekend, but my CPV spread was only 10 mV and I had a lot of heat from spirited driving and QC'ing.

 

[DaveEV]

More interesting balancing behavior today after charging to 100% (normally charge to 80%) in an attempt to balance the pack some.

Almost 2 hours after charging finished, battery balance is already 10 mV tighter than my earlier post. Still have a lot of room for improvement - my lowest cell is 20 mV below the average - closer to 30 mV if one assumes that 4.1 V is "perfect". That could be quite a bit of capacity I'm leaving on the table.

I decided to L1 some more to see what'd happen. The car accepted about 40 minutes of L1 which pushed up cell voltages 9-15 mV - naturally the lowest CPs stayed lowest and one of the highest CPs went higher.

80 more minutes of sitting and the pack has balanced more.

Hmm, after driving 12 miles the balance has gotten worse? I would normally expect the pack to be go towards better balance towards the middle of the pack.

WTF? After sitting for 10 hours in low-mid 70s temperatures, the balance has gotten even worse with a strange divide between CP 1-48 and the rest of the pack??

Drive 12 mi back home and the pack balance is looking "normal" again.

I'm very confused!

 

[Stoaty]

I hit a low of 85.81% CAP this weekend, but my CPV spread was only 10 mV and I had a lot of heat from spirited driving and QC'ing.

That is the biggest temperature difference I have seen (so far) at 7.4 degrees between max and min!

 

[FairwoodRed]

That is the biggest temperature difference I have seen (so far) at 7.4 degrees between max and min!

Two nights ago, after driving all night and 2 QC's, I had a spread of almost 10 degrees... This morning I was down to 4 degrees.