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TickTock
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Leaf Number: 3626
Location: Queen Creek, Arizona
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Re: Optimal charging at 20% SOC, 6 temp bars, cool ambient t

Tue Jul 03, 2012 7:59 am

When I arrive home, I am closer to 10%. I have been considering installing a hot water timer inline with my AV charger to cut the power for 30 minutes about 2 hours after I typically arrive home. Then, when I get home I just have to hit the override to charge until the water timer cuts it off which should get me above the 30% line. Then the car will finish in the morning since I set the END timer only. *I think* this will work - I know that if I come out and unplug and replug it in it will stop the manual override and revert to the timer settings. Seems reasonable that a power outage will have the same effect.

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surfingslovak
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Re: Optimal charging at 20% SOC, 6 temp bars, cool ambient t

Tue Jul 03, 2012 7:59 am

mkjayakumar wrote:Given that Leaf has 24kWh (I was told in this forum), then wouldn't an 100% usable charge of 21 kWh is actually ony 87%, and an 80% charge (which is 16.8kWh) in reality only 70% ?
I believe that Phil managed to get exact SOC readings out of the battery ECU and determined that full charge corresponded to 94 or 95%. 80% charge is what it says, and not less, as many of us have previously assumed.

In addition to what's been already said, please consider that the charge sustaining mode on the Volt kicks in around 22 or 23% SOC. Presumably, you can drive the vehicle in this mode for months on end, and GM engineers thought that this SOC offered a good trade-off between range and battery longevity. I would not be concerned to let the Leaf sit at 20%, but if it was parked for an extended period of time (days and weeks), I would bring the SOC above 35% if possible.

The charts we are looking at are usually for generic LnMnO4 cells and they don't apply 100% to the Leaf. I would use them to get an idea of the characteristics and behavior of these cells, not an exact prediction of how the Leaf will behave. In addition to manganese dissolution in electrolyte Dave posted above, there are other processes that degrade the battery. I believe that at low SOC, Jahn-Teller effect will start impacting the spinel structure of the cell.

The owners manual (page EV-23) and these studies give us an idea of the speed of these processes as well. Dissolution into electrolyte, which seems to be dominant at high SOC, is typically measured in a matter of days. Spinel distortion due to Jahn-Teller effect is measured in a matter of weeks.

As a practical recommendation for a daily routine, I would try to keep the Leaf above the low battery warning (17% SOC). Dipping down to the very low battery warning (8% SOC) should be no problem, but you might not want to do it as part of your daily routine if possible (Luke is probably exempt from this). Turtle mode appears to be set fairly conservatively from a cell voltage perspective, but the SOC is so low that I would be concerned, and would not recommend doing that on a regular basis.

If you look at the annual battery report that Phil posted earlier, Nissan keeps track of the number of turtle events and the number of hours spent at high SOC. It's pretty clear that they are doing this, because they think that it will impact battery performance. Note that they are lumping low SOC (0-20%) into one band and high SOC (>85%) into another (PKTIMEWHENHIGHSOCAFTERCHARGE, PKTIMEWHENHIGHSOCAFTERDRIVE, SOCATCG and TURTLELAMP).

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chris1howell
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Re: Optimal charging at 20% SOC, 6 temp bars, cool ambient t

Tue Jul 03, 2012 12:14 pm

LEAFer wrote:+1. And sounds like a chris1howell project to me ... hint ... hint ;)
I have been thinking about changing the charge rate over time... Kinda backwards from this topic. For Example on a 80A breaker you can use up to 80A non-continuous. If the load is continuous (over 3 hours) than you can use only 80% of the breaker value. So I was thinking of adding a mode to charging at 100% of the breaker rating for the first 2 hours and 59 minutes and then drop to 80%.

With OpenEVSE it would be pretty easy to come up with a charge rate curve based on time or just simply charge for 2 hours then go to ready to wait for the charge timer. There is already a charge timer running during charge on OpenEVSE.
2011 LEAF: Red SL #04122
2012 Tesla Model S #01530
EVSE: OpenEVSE, 40A L1/L2 -- http://www.openevse.com
PV System: 28 x 210W -> 5.8 kW DC

OpenEVSE Store: http://store.openevse.com

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RegGuheert
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Re: Optimal charging at 20% SOC, 6 temp bars, cool ambient t

Tue Jul 03, 2012 12:31 pm

chris1howell wrote:I have been thinking about changing the charge rate over time... Kinda backwards from this topic. For Example on a 80A breaker you can use up to 80A non-continuous. If the load is continuous (over 3 hours) than you can use only 80% of the breaker value. So I was thinking of adding a mode to charging at 100% of the breaker rating for the first 2 hours and 59 minutes and then drop to 80%.
That sounds interesting, particularly for a L1 charger. Chris, what is involved in the EVSE changing the charging current while charging? Does it require the EVSE to terminate the charge and then submit a new pilot, or is there some way to renegotiate the current level while the charging is ongoing? (Sorry, I'm just not familiar with the protocols.)

TIA!
RegGuheert
2011 Leaf SL Demo vehicle
10K mi. on 041413; 20K mi. (55.7Ah) on 080714; 30K mi. (52.0Ah) on 123015; 40K mi. (49.8Ah) on 020817; 50K mi. (47.2Ah) on 120717; 60K mi. (43.66Ah) on 091918.
Enphase Inverter Measured MTBF: M190, M215, M250, S280

chris1howell
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Re: Optimal charging at 20% SOC, 6 temp bars, cool ambient t

Tue Jul 03, 2012 12:54 pm

RegGuheert wrote:what is involved in the EVSE changing the charging current while charging? Does it require the EVSE to terminate the charge and then submit a new pilot, or is there some way to renegotiate the current level while the charging is ongoing?
The EVSE changes the pilot duty cycle and the EV has 5 seconds to comply.
2011 LEAF: Red SL #04122
2012 Tesla Model S #01530
EVSE: OpenEVSE, 40A L1/L2 -- http://www.openevse.com
PV System: 28 x 210W -> 5.8 kW DC

OpenEVSE Store: http://store.openevse.com

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RegGuheert
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Re: Optimal charging at 20% SOC, 6 temp bars, cool ambient t

Tue Jul 03, 2012 1:03 pm

chris1howell wrote:The EVSE changes the pilot duty cycle and the EV has 5 seconds to comply.
O.K. Sounds straightforward. Thanks!
RegGuheert
2011 Leaf SL Demo vehicle
10K mi. on 041413; 20K mi. (55.7Ah) on 080714; 30K mi. (52.0Ah) on 123015; 40K mi. (49.8Ah) on 020817; 50K mi. (47.2Ah) on 120717; 60K mi. (43.66Ah) on 091918.
Enphase Inverter Measured MTBF: M190, M215, M250, S280

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abasile
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Re: Optimal charging at 20% SOC, 6 temp bars, cool ambient t

Tue Jul 03, 2012 10:04 pm

Thank you for the responses, particularly surfingslovak's detailed and informative reply! Trying to gauge the actual battery temperature, as suggested by garygid, is not a bad idea.

In general, it seems sensible for daily driving to try to use the LEAF's battery within parameters similar to those imposed by the more conservative Volt. In terms of SOC, my commute is pretty close to that, as my daily SOC range is roughly 20% - 80%. Beyond that, one can "safely" charge to 100% daily if charging is completed shortly before driving. Based on Tony Williams' experience turtling his 2011 LEAF on many occasions and subsequent capacity loss, however, it indeed seems like a very bad idea to frequently use the very low end of the battery.

Back to my original question, I think I'll continue charging to ~40% upon arrival from work, even if only to have some reserve in case we decide to go somewhere that evening. But if I have reason to believe the pack is particularly hot (closer to 98 F), I'll probably hold off on charging.
2011 LEAF at 71K miles, pre-owned 2012 Tesla S 85 at 98K miles
LEAF battery: 9/12 bars and < 49 Ah (-28% vs. new)
Tesla battery: 250+ miles of range (-5% vs. new)

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planet4ever
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Re: Optimal charging at 20% SOC, 6 temp bars, cool ambient t

Tue Jul 03, 2012 11:24 pm

surfingslovak wrote:
mkjayakumar wrote:Given that Leaf has 24kWh (I was told in this forum), then wouldn't an 100% usable charge of 21 kWh is actually ony 87%, and an 80% charge (which is 16.8kWh) in reality only 70% ?
I believe that Phil managed to get exact SOC readings out of the battery ECU and determined that full charge corresponded to 94 or 95%. 80% charge is what it says, and not less, as many of us have previously assumed.
The other piece of this that mkjayakumar may have overlooked is that zero usable charge (dead turtle) is not 0 kWh in the battery. So if you have 21 kWh usable it might be from 2 kWh minimum to 23 kWh maximum. (I'm not claiming those are the real numbers - just pointing out that the origin is not really zero, and that messes up assumptions you may have on % calculations.)

Ray
End of April 2013: Traded my 2011 SL for a 2013 S with charge pkg.

Herm
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Re: Optimal charging at 20% SOC, 6 temp bars, cool ambient t

Wed Jul 04, 2012 4:09 am

surfingslovak wrote: If you look at the annual battery report that Phil posted earlier, Nissan keeps track of the number of turtle events and the number of hours spent at high SOC. It's pretty clear that they are doing this, because they think that it will impact battery performance.
Battery Life.. but otherwise what you said :)

Keep the battery as cold as possible and in the 20-80% range for longevity, and never fast charge when the battery is near human body temperature.

Per Phil a GID is the stored power in the battery, full charge at 281 GID (95%) and contactor opens at 5 GID (2%).. so a total of 276 GID is stored when the car is new, 22kWh. If the computer allowed us to charge up to 300 GID then the total stored energy would be 24kWh, battery life would be very short.

Thus 22kWh is the usable energy when the car is new... but note that not all of that will end up on the road due to motor and inverter losses, but those are dependent on how you drive thus different for everyone.

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