March 2017 Drive Report; Battery Health Update

This month was unusual for several reasons. I am still trying to collect as much data on battery cooling as I can by checking the pack at random intervals between fast charges.  To reduce outside influences as much as possible, I am only collecting measurements when there was no L2 charging during the interval.

This meant a lot of charging on the road with charging before and after work common.  I soon began to realize that someone living in a situation where home charging was not practical could actually get away with all public charging with just a few well placed stations.  Yes, I did get out on the road early a few times and no there isn't as much to do in the morning to cover that time (other than Facebook, etc.) but early is something I do often so it was mostly a question of sitting at home before work or sitting at a charger before work.

The afternoons were easier because every job requires work at home and I simply did it while charging. Since this is a billable event,  I am getting paid and it does lessen the work I need to do when I get home so its a wash on time demands. All this really means that my weird work schedule simply gets weirder.

For the month, the LEAF traveled 2501.3 miles costing $32.65 or 1.3 cents per mile. My home costs dropped from 9.2 cents per kwh to 8.9 cents per kwh.  I collected 365 kwh from NCTC. I had 9 days over 100 miles driven which includes one 300 mile day and two 200 mile days.

Battery Health Update;  No changes from new @ 7980 miles.

My pack balance is more than twice the delta of my 2013 pack but only went to "L2 full charge" seven times during the month but only once (the 300 mile trip) during the 2nd half of the month.  With balance averaging 20-25 mV,  not extreme but a far cry from the frequent single digit readings my 2013 pack normally displayed.

All this got me thinking about just how effective pack balancing was when sitting in garage all night and I found that it... well wasn't.  No improvement overnight in the balance. In many cases it was worse in the morning than it was the previous night.  Now, I know there is a lot of noise in these readings including temperature, recent charges and discharges, etc but even when allowing car to sit for at least 4 hours before taking baseline measurements, I was still seeing no changes.

But when the car is on and running or charging (remember, I have a LOT of recent experience with the latter!) nearly all my shunts are active. Generally, I see 5-20 blues so nearly all red all the time so what are these shunts doing cause the results seem pretty slim??

So I decided to see if I could determine how many were active after the car had sat a while. Well, problem is that without the pack connected, LEAF Spy doesn't show everything but it did allow me to see that the shunts come on in waves.

So now the question becomes what are we seeing here?  There is really only two plausible explanations;

1) The load of the car turning on is enough to initiate balancing among all the red cells

2) None of the cells were actively balancing until the car was turned on and the traction pack engaged. It was only after the BMS was active that the pack started sending out balancing requests.

Now first off, yes I know that there were a few red ones right off the bat but LEAF Spy shows old data until new data is read so what you see initially is primarily previous readings from the last power down or last time LEAF Spy was logged off.  Yes, we see codes running in the background but I think those are related to the other stuff like tire pressures, charge counts, etc.

Now when the car is turned on we notice first the reset to all blue and 11 mV delta but as the red ones come on, the delta increases accordingly.  I had everything off and unfortunately, LEAF Spy does not measure loads, it only parrots back what the LEAF is telling it so all we had active was a "standard" 200 watt accessory load which is not actually measured according to Phil (Peef at Priuschat.com or Engineer (sp?) at mynissanleaf.com) the creator of EVSEupgrade.com.

Either way, there is evidence that supports both explanations above so I need your help. I know there is someone out there that has already answered this question so chime in so we can all find out (or at least allow me to be the last one to come in from the cold)

I guess my other option is to simply power up the car, turn off as much as I can and let it sit a few hours or so to see if there are any demonstrable improvements in pack balance which is what I am actually doing this very minute.  I would have done it sooner but opportunities for this have been slim lately!

So let me know!
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Oh wait!.. almost forgot. The Corolla went 62.7 miles costing a few bucks or something like that.  In reality it was my plan to have ditched that car by now but Chevy is simply not allowing that to happen so probably have to tolerate its presence in my driveway for another 7-8 months or so!