maintaining a low SOC to preserve battery life

[DaveinOlyWA]

Four 100% charges three days in a row all in the low 240s gid. It's 3.5% loss not 4%, in one month, I got a 250 gid on 8/5/12.

you had warm temps. you probably lost 5+% from that. i am predicting it will come back.

 

[gbarry42]

A "colorization" for the charge bars is:
12 [RED]
11 [RED]
10 [YELLOW]
9 [YELLOW]
8 [YELLOW]
7 [GREEN]
6 [GREEN]
5 [GREEN]
4 [GREEN]
3 [GREEN]
2 [RED]
1 [RED]

You're imagining something like this?

 

[JeremyW]

You're imagining something like this?

Yes sir! My gels are on the way, hope to make a real one on Friday or Saturday. Just in time for plug in America day.

Mind if I throw that pic in the first post in the thread?

Oh and I was able to get to 5 TB and keep it all the way to work this morning! Although I couldn't get a spot under the solar shading today... C'est la vie. :roll:

 

[gbarry42]

Sure, go ahead. Looks good enough to show the idea, at least.
And, stay out of the sun

 

[Herm]

That looks really nice.. I would get rid of one of the yellow bars, and both red bars on the low SOC end.. perhaps just a single orange bar at the LBW end to replace the two yellows. Just having those two red bars at the top will prevent lots of early (less than 5 years) battery damage

 

[DaveinOlyWA]

i will assume that the color chart should be on the TBs right?

 

[tbleakne]

I believe that we have no evidence to support the idea that keeping the
LEAF's battery below 5 or 6 bars is any better than keeping it below
the 8 to 9 bars level.

However, keeping the battery cooler seems to reduce the aging effect.

I joined the "50% Club" in July, but I haven't had time to catch up on this thread. Thanks, Jeremy, for starting it.

In support of others who have posted on this thread their opinion that SOC below 80% helps, here is a re-posting from another thread of some "evidence" I found recently:

Sandia National Laboratories studied lithium-ion battery loss as a function of both temperature and DOC:
http://144.206.159.178/ft/641/92454/1607538.pdf

Capacity fade is discussed on pg 7, Fig 5, which I display below:

The chart shows that capacity fade generally slows for all temperatures as the DOC is reduced from 100% to 80% to 60% SOC. At high state of charge the Li-ions are concentrated on the anode. My understanding is that the primary loss process takes place at this electrode, so it seems reasonable that this process would slow as the SOC lowers.

This 2003 paper is obviously not talking about the LEAF's particular Lithium chemistry, but I believe the behaviors it describes are typical, especially since the Lithium cells in both this study and our LEAFs use carbon for the anode.

Keen-eyed observers of my original posting pointed out that the 55 C curve (triangles) appears to show more capacity fade at 80% than at 100%. A closer examination seems to show that the 80% curve does better up to 15% fade, and then it starts rising faster than the 100% curve. I can't explain this anomaly, other than to note that 55 C is quite toasty (131 F), and possibly a different chemical process becomes involved. 60% DOC appears to show definite improvement relative to 80%, although there is also an anomaly on this chart where the 45 C curve is initially lower than the 35 C curve.

 

[JeremyW]

My sample pack of gels came in. Here's a pic of me trying out colors on the capacity bars. The effect is pretty cool but hard to photograph. I'm using orange for the upper bars instead of red and yellow for now. It matches the start button to symbolize that if you charge to this level, you should be driving instead of letting it sit.

More tomorrow.

 

[JeremyW]

Work in progress.

 

[JeremyW]

Just wanted to give an update on how this new gauge face is working. I find it very easy to count out the bars and know where I "should" be for best battery life. Since my town is pretty small and I have both home and work L2 charging, I can live with this reduced range pretty easily. My 5 green bars get me through about 2 or 3 days of around town driving. I usually know when I'll be needing the extra charge (like a bay area meeting! ) and go to 80% or 100% when I need to.

I have to admit- I'm attached to the rest of the car. There's a lot that is done well. There's a good chance I'll buy out the lease even if it doesn't make the best financial sense. I already am planning a second life for my battery as part of my future house, so there is good reason for me to treat the pack kindly, even if I don't officially own it yet.

The good things going for my battery:
I'm basically mimicking how the volt treats its battery by staying within the ideal state of charge "window". Since the traction pack is warranted for 10 years or 150,000 miles in California, I imagine they took longevity very seriously. While there's no TMS like the Volt to keep my battery temperature in the ideal range, I do vent my garage with fans. The night time low is in the 60s (should start moving to the high 50s this weekend) and with fans directing the cool night time air under the car I have been successful in getting 5 bars in the morning that stay till lunch. I have solar shading at work most days, however my work charging stations are not shaded. I do the majority of my charging at work between 8-11 am.

The bad things going for my battery:
I do quick charge a lot on the weekends and drive like a bat out of hell. I'm running a 3.9 mi/kWh average. I also think my dealer left the car at a high state of charge for a few months before I got it. It's got a pack from Feb 12 and I didn't get it till the end of June. Luckily the weather in Costa Mesa is mild. My gid count on my second or third charge was 271. I do not currently have a gid meter.

Is this practical for most people? Probably not. If the pack size was double, maybe. Why I'm doing this is to prove what is possible if you treat lithium batteries like they should be treated. Only lead acid likes to be charged to full. The rest like to stay around 50%, with 30% being the ideal storage SOC for lithium. Oh, and all batteries hate heat. :roll:

 

[surfingslovak]

Good work, Jeremy! Would you have any more recent photo of the gauge?

 

[pchilds]

Four 100% charges three days in a row all in the low 240s gid. It's 3.5% loss not 4%, in one month, I got a 250 gid on 8/5/12.

The date of my 250 reading was 7/22/12, before the 2-3 weeks of 110+f highs in August.

Update: I have recover all GIDs lost in August, looks like my efforts were successful. Last five 100% charges 249, 250, 249, 250, 250. My lowest was plug in day at 235, thought for sure I would lose my first bar any day.

 

[RegGuheert]

Four 100% charges three days in a row all in the low 240s gid. It's 3.5% loss not 4%, in one month, I got a 250 gid on 8/5/12.

The date of my 250 reading was 7/22/12, before the 2-3 weeks of 110+f highs in August.

Update: I have recover all GIDs lost in August, looks like my efforts were successful. Last five 100% charges 249, 250, 249, 250, 250. My lowest was plug in day at 235, thought for sure I would lose my first bar any day.

That's good news! So my question is if you didn't lose any GIDs this summer, when did you lose the first 31 GIDs? Are we seeing the major leveling-off that Nissan has always promised? Or did you have a very different charging regime in the past?

 

[pchilds]

That's good news! So my question is if you didn't lose any GIDs this summer, when did you lose the first 31 GIDs? Are we seeing the major leveling-off that Nissan has always promised? Or did you have a very different charging regime in the past?

July 22nd was my first was my first GID reading, after charging to 100% three times in a row. The below link covers the what I have done to reduce battery capacity loss.

http://www.mynissanleaf.com/viewtopic.php?f=27&t=9400

 

[ERG4ALL]

I recently took my Phoenix based LEAF into the dealer for a battery check and software upgrade. I was surprised at the results. First, let me say that the car has never had to endure a Phoenix summer. The battery heat gauge has never been above six bars. In the summer the car is in the mountains where a really hot day is 90 degrees. Second, the amount of times I've "floored" the accelerator you can count on both hands after 19,000 miles and 19 months of ownership. Our starts and stops are gentle but not obstructive to other traffic. We charge to 80% nearly all the time. When we need to charge to 100% (which is maybe 5% of the time) we charge to 80% and then punch it up to 100% and time it so that we drive the car immediately after reaching 100%. Our car has never been QC'd.

When the battery check was complete, the battery scored five stars on all ratings. I got to talking with the mechanic that did the software upgrade and the battery tests and he agreed to check the battery with a full charge to see the total capacity of the battery. One indicator is the maximum voltage that the battery can hold. He said that a new battery will register between 400V to 425V. When he checked ours at full charge it was 396V. Thus, my experience has been that the battery could well last 8 years with a 20% drop in capacity.

Because I haven't been able to change my email address (my old address does not appear in a white background), I may be tardy or overlook any questions regarding my experience so send me a PM.

 

[garygid]

I have never seen a LEAF battery pack over 396 volts
while at rest, but I have not seen all batteries in
all circumstances.

I suspect that the service guy's voltages
are only observed when the battery pack
is charging, maybe even while doing a QC.

 

[ERG4ALL]

I watched him while he did it. What we may be seeing is that there was no immediate drop off after disconnection. We both were watching the L2 charger lights as they were blinking the last bit of charge. Just as soon as they stopped the mechanic unhooked the car from the charger and hooked up his laptop and plugged it in and got the reading. It may have been a better test to let the battery cool for an hour and then checked it's static reading, however, that is impractical at the dealer. At any rate, I'll keep on doing what I've been doing so when the lease is up in another 19 months Nissan can't say that the car has been abused. I've never leased a car before so I don't know how much of a stickler they are on "normal wear and tear".

 

[DaveinOlyWA]

Label me confused sjnce people with lost capa ity have not lost voltage. I have never seen more 394 v and it usually 392.5-393

Dont know if Li is different but my ZENN always read higher after a complete charge. Waiting an hour is the least i would do

 

[Herm]

That battery will still read 396V even after it has lost 50% capacity a few years from now.. the mechanic is probably thinking of 12V lead acid batteries but that does not apply at all to lithium-ion

 

[DaveEV]

I got to talking with the mechanic that did the software upgrade and the battery tests and he agreed to check the battery with a full charge to see the total capacity of the battery. One indicator is the maximum voltage that the battery can hold. He said that a new battery will register between 400V to 425V. When he checked ours at full charge it was 396V.

Battery voltage when fully charged is not an indicator of battery capacity - it is only an indicator of how fully charged the battery is. Frankly, the mechanic doesn't know what he's talking about.

I very, very highly doubt that you will see anything more than 396V when the car is fully charged and anywhere from 392-394V is typical when the voltage is read using a GIDmeter.

If you ever saw more than 412V in the LEAF (4.3V/cell), you would be in danger of permanently damaging your battery.