RegGuheert
Well-known member
This winter has been quite a bit colder than last, so I am having my first experiences with driving the LEAF in temperatures below 10F. I know others do this frequently, but I don't recall any previous discussion of large cell imbalances as a result of driving in the cold.
What I find is that the battery pack in our LEAF is constantly much more imbalanced than I am used to seeing. In warmer weather, the cells in our LEAF tend to be within about 20mV or so. Not so this winter! Yesterday, I was driving on a highway in 10F weather at about 60 MPH. If I was consuming about 30 kW while climbing a hill, I saw a voltage range of 60 mV...and this was with a 60% SOC! The signature was clear: The bar graph on LEAFSpy looked like a rectified sine wave: The first 48 cell-pairs (which are the ones under the back seat) were low on the ends and high in the middle. The same was true of the other 48 cell-pairs (which are under the front seats and the rear footboard). It appeared that the cell-pairs on the outside of the rear stack were colder and therefore had much more voltage drop than those in the center. A similar effect seemed to also occur with the front stacks, although their relative thermal properties are much less obvious to me.
Well, today I went out on the same 26-mile trip, but I had little notice, so I left with only 55% SOC. I figured I would arrive home with more than 20% SOC, so no problem. Well, I was right, I got back with 20.1% SOC, but not before hitting LBW at 25.7% and VLBW at 20.8%! After letting the LEAF sit quietly for a little while in the garage to let the cells settle down, I noticed that there was a 235 mV difference between the lowest and highest cells! (Cell-pair 37 was the lowest at 3.375V and cell-pairs 1 and 32 were next at around 3.422V.) Battery temperatures ranged from 35.1F to 38.0F.
The LEAF had last been charged to 100% yesterday and typically gets charged to 100% roughly once each week. The car has 16,613 miles on it and currently shows a capacity of 58.67 Ah and a Hlth of 86.90%.
So I am wondering the following things:
1) Is this what others normally see for the LEAF cell balance when the car is driven down to 20% SOC in extremely cold weather?
2) The minimum cell-pair voltages is below the 3712 mV specified in the service manual for the CELL VOLTAGE LOSS INSPECTION test. Should I be alarmed that cell-pair 37 is right at the judgment value for replacement as calculated in the service manual? (Judgment value: 3.37V Cell-pair 37: 3.375V
3) Was I about to hit turtle even though the battery showed it still had a 20% SOC? If not, why not? (It seems that cell-pair 37 was headed south and a few others were not too far behind.)
I guess I'm a little bit concerned that I left home with 55% SOC and consumed only about 35% of that SOC, but apparently nearly came up short. That would not have been a pleasant outcome when it is 10F outside.
Thoughts?
What I find is that the battery pack in our LEAF is constantly much more imbalanced than I am used to seeing. In warmer weather, the cells in our LEAF tend to be within about 20mV or so. Not so this winter! Yesterday, I was driving on a highway in 10F weather at about 60 MPH. If I was consuming about 30 kW while climbing a hill, I saw a voltage range of 60 mV...and this was with a 60% SOC! The signature was clear: The bar graph on LEAFSpy looked like a rectified sine wave: The first 48 cell-pairs (which are the ones under the back seat) were low on the ends and high in the middle. The same was true of the other 48 cell-pairs (which are under the front seats and the rear footboard). It appeared that the cell-pairs on the outside of the rear stack were colder and therefore had much more voltage drop than those in the center. A similar effect seemed to also occur with the front stacks, although their relative thermal properties are much less obvious to me.
Well, today I went out on the same 26-mile trip, but I had little notice, so I left with only 55% SOC. I figured I would arrive home with more than 20% SOC, so no problem. Well, I was right, I got back with 20.1% SOC, but not before hitting LBW at 25.7% and VLBW at 20.8%! After letting the LEAF sit quietly for a little while in the garage to let the cells settle down, I noticed that there was a 235 mV difference between the lowest and highest cells! (Cell-pair 37 was the lowest at 3.375V and cell-pairs 1 and 32 were next at around 3.422V.) Battery temperatures ranged from 35.1F to 38.0F.
The LEAF had last been charged to 100% yesterday and typically gets charged to 100% roughly once each week. The car has 16,613 miles on it and currently shows a capacity of 58.67 Ah and a Hlth of 86.90%.
So I am wondering the following things:
1) Is this what others normally see for the LEAF cell balance when the car is driven down to 20% SOC in extremely cold weather?
2) The minimum cell-pair voltages is below the 3712 mV specified in the service manual for the CELL VOLTAGE LOSS INSPECTION test. Should I be alarmed that cell-pair 37 is right at the judgment value for replacement as calculated in the service manual? (Judgment value: 3.37V Cell-pair 37: 3.375V
3) Was I about to hit turtle even though the battery showed it still had a 20% SOC? If not, why not? (It seems that cell-pair 37 was headed south and a few others were not too far behind.)
I guess I'm a little bit concerned that I left home with 55% SOC and consumed only about 35% of that SOC, but apparently nearly came up short. That would not have been a pleasant outcome when it is 10F outside.
Thoughts?
