Study Ideas - Battery Degradation

i'm up to about 15 miles at an average of 18-20 mph on flat ground, slow acceleration, few stops and no hvac. that's down from about 16.5 when new. i think there is something wrong with that charge point reading. i don't think you can get 13 or 14 on 2.5 kWh.

 

hmmm... maybe mine is way down too. i wonder how far @jerrymildred can drive if he's careful.

 

I wonder about that, too!

As you know, there are VERY few route options here unless you want to drive an extra 15-20 miles or more. My daily commute is almost all 45-53 mph with lots of stops -- many of them last second as the badly timed lights do their thing to waste fuel and pollute the air. And there are NO low speed options unless I had an air boat. Even with those 50+ mph speeds, I only average 17 mph to and from work. That's how bad it is. Then there's the 95° temperatures and the A/C load. Most times, my computer forecasts a 12.1-12.4 mile range. 12.4 is the highest I've ever seen. Then I turn on the A/C and watch it plummet.

BUT! This morning I went to take care of the yard at a snowbird friend's house. That was all 45 or under, mostly 30, about 3.5 miles each way running A/C in normal mode to try to cool the battery. Traffic was light, so I could do some hyper-miling, even putting it in neutral sometimes to glide up to the lights. When I got home, I plugged it in again before running another local errand or two. I unplugged it to go before it was done and it said I had an expected 12.5 miles. That was a first and it wasn't even done yet! (But probably very close.)

One of these days, I may overpower my frugality and just drive around the residential areas to see how far I really can go at 40 mph or less in light traffic. In fact, I may do that soon now that you've further stirred my curiosity.

BTW, so far, this is my best tank ever. After around 160 miles, I'm averaging about 127 mpg. That won't last, though, since I have some distance to cover Sunday.

 

Here are my last 6 charges at a Chargepoint charger at work. I only use the Chargepoints at work on days when I ran out of juice well before getting to work (about 4 miles of HV).

March 21 2017: 2.559 (high 60s)
April 3 2017 : 2.567 (low 70s)
April 17 2017: 2.549 (high 70s)
May 4 2017 : 2.518 (low 70s)
May 19 2017 : 2.561 (mid 80s)
June 19 2017 : 2.574 (high 80s)

I charge 2x per day, Level 2 at home, usually Level 1 at work. I also always use timed charges so it charges up right before I leave for work/home.

 

track, do you have records from new?

 

you'll need to do it a 5am with no hvac.

 

So, we didnt get the Chargepoints installed until Sept 2013. I used them exclusively until Feb 2014 until they allowed people to go back to using some of the dedicated 120V outlets from before due to "over crowding"" at the time. During this period though, I wasnt running out of juice daily, so those numbers are not helpful.

My daughter started high school Sept 2015 and I drive carpool one or two days a week. On these days, I'll run out of juice before getting to work. So thats when I came up with the idea that I'd use CPs on those days. But since we have like 40 EV/PHVs at work and a limited number of chargers, you have to move when you're done. Whereas if I plug in at the 120Vs, I can sit there all day long (in the shade even). So I dont consistently use CPs even on days when I "could". I just wanted to get an idea over time how it was doing.

So with that long winded explanation, here are all the data points I think we can use. There are some days I weeded out because I may have driven to pick up lunch or whatever, so they were slightly higher (like 2.7+).

Looking at this data, its pretty clear I'm using less juice. Not a whole lot, but its definitely degrading. I have some co-workers with newer PiPs I may be able to get data from. But I have to make sure they are charging on empty.

Sept 15 2015 : 2.686
Sept 24 2015 : 2.651
Oct 29 2015 : 2.642
Nov 5 2015 : 2.567
Nov 12 2015 : 2.608
Nov 19 2015 : 2.580
Dec 10 2015 : 2.620
Dec 14 2015 : 2.608
Dec 15 2015 : 2.610
Dec 29 2015 : 2.590
Jan 7 2016 : 2.590
Jan 14 2016 : 2.641
Apr 21 2016 : 2.645
Jul 26 2016 : 2.676
Oct 7 2016 : 2.558
Nov 8 2016 : 2.587
Jan 27 2017 : 2.566
Feb 6 2017 : 2.564
March 21 2017: 2.559 (high 60s)
April 3 2017 : 2.567 (low 70s)
April 17 2017: 2.549 (high 70s)
May 4 2017 : 2.518 (low 70s)
May 19 2017 : 2.561 (mid 80s)
June 19 2017 : 2.574 (high 80s)

 

Here's a graph of the data.. it looks scary.. but its just based on # of sessions.. not over the correct period of time.. but the general trend is still down (with the exception of the middle, in the summer months)

man, the forum is coming apart!

 

@Tracksyde, no kidding!! Unusable yesterday. Only horrible today. Maybe, if they ever get it working, I'll be able to see your graph. Now, to see if I can actually post this.

 

jerry, how do tracks #'s compare with yours?

 

Yay! I can see his graph now!

@Tracksyde's numbers are lower than mine. My full charges are always over 3 kWh -- usually around 3.2 to 3.4 on my Killawatt meter. But it could be that either his or my meter is off a bit -- or maybe both of them. I think I might be able to come up with a formula using the car's info combined with the Killawatt to get an idea whether my meter is reasonably accurate. I'll have to ponder that one. Just by seat of the pants guestimation, I think it's close. I also need to figure out how to generate a graph in Excell because I'm really rusty at that program.

As for miles per kWh, I get 3.62-4.04, but those are pretty demanding driving conditions. I just might follow your suggestions and get up early tomorrow or Monday and take a drive up Grand and Madison streets to use up a full charge to see how it does under more favorable conditions (35 mph limits, fewer stops, not screaming hot). I want to do the same route today for a summer baseline. Here's a picture of what the car shows for miles per kWh with the average at the top:

 

track, have you done a low speed drive to judge available ev distance?

 

agreed, total ev miles would be a good stat to know, for anyone who has kept track.

 

Well, that was dumb! I headed out on my baseline drive and 3 blocks down the road I noticed that I hadn't reset my trip meter. DOH!! Re-topping the battery. And, with the overcast and the several inches of rain we got this morning, I'm going to try doing it w/o air conditioning. But, as they say, if I'm not comfortable, neither is the battery. At worst, the A/C will be loafing rather than straining.

I can''t get over how many more miles per kWh some of you get than I do. Hopefully, this drive and one in even better conditions in the near future, will give me a better idea what's going on since my regular routes are so crazy.

Edit to add: @bisco, I have the total since I got the car. It was 3,546 as of last week when I got gas. That's vs. 4,927 in HV.

 

Maybe. The monthly mileage columns when I got it showed pretty high numbers, though for the previous 5-6 months other than the time it was waiting for me to buy it. Who knows how typical that was, though?

 

looking at the spread sheet, my miles/kwh seem to have trended up a bit over the years, even though total range is reduced. maybe break in and old tyres?
someone screwed up the spreadsheet though, so it's hard to be sure. i have asked ken to fix it.