User avatar
Ingineer
Posts: 2741
Joined: Fri Oct 15, 2010 1:09 pm
Delivery Date: 13 Jul 2011
Leaf Number: 6969
Location: Berkeley, California
Contact: Website

Real SOC (State of Charge) - Information

Mon Mar 19, 2012 1:00 am

It was recently asked how I derive SOC for LEAFSCAN. This number is simply obtained from the Battery ECU, and is displayed as-is. The various Leaf systems use this as a basis for making operational decisions and displaying information. The SOC is created by coulomb counting, which is basically defined as counting the electrons passing in/out of the battery. Due to the fact that it's not actually possible to do this very accurately in a mass-produced EV, the battery ECU periodically makes adjustments to keep the SOC as accurate as possible. One of the main ways this is done is by checking open-circuit voltage of the pack and applying some math to correct this number for things that will affect it, and using a lookup table of known states. This all working together makes for a pretty accurate SOC calculation. The Leaf's engineering team make use of a hall-effect based current monitor to perform the coulomb counting, and these have a number of issues that make them less accurate than ideal, but they are cheap and good enough.

The reported SOC usable range seems to be from about 95% (fully charged) to 2% when the battery main contactor opens up and disconnects the pack. The first low battery warning occurs at around 18%, and the second one at around 9%. If I remember correctly, Turtle mode comes on at about 5%, and begins limiting power. At about 2%, you are totally dead.

-Phil
Easily Learn Electricity HERE! - - - - Website: http://evseupgrade.com/ - - - - Like us on Facebook: EVSE Upgrade

User avatar
TonyWilliams
Posts: 10085
Joined: Sat Feb 19, 2011 1:48 am
Location: San Diego
Contact: Website

Re: Real SOC (State of Charge) - Information

Mon Mar 19, 2012 1:12 am

Ingineer wrote:The reported SOC usable range seems to be from about 95% (fully charged) to 2% when the battery main contactor opens up and disconnects the pack. The first low battery warning occurs at around 18%, and the second one at around 9%. If I remember correctly, Turtle mode comes on at about 5%, and begins limiting power. At about 2%, you are totally dead.

-Phil


So, with any of fancy testing, does this look reasonable?

Code: Select all

Gid%       Gid Value  SOC%
100.0%     281          95

91.5%      257

84.0%      236

77.9%      219

70.8%      199

66.2%      186

58.0%      163

50.9%      143

43.4%      122

36.3%      102

31.3%       88

26.0%       73

17.4%       49        18 (LBW)

8.9%        25         9 (VLB)

1.4%        4          5 (Turtle)

???         2          2 (dead)

User avatar
Ingineer
Posts: 2741
Joined: Fri Oct 15, 2010 1:09 pm
Delivery Date: 13 Jul 2011
Leaf Number: 6969
Location: Berkeley, California
Contact: Website

Re: Real SOC (State of Charge) - Information

Mon Mar 19, 2012 1:54 am

TonyWilliams wrote:So, with any of fancy testing, does this look reasonable?
Yes. Just as you see the top-end "Gids" vary from charge to charge, the SOC also varies a bit.

Keep in mind "Gids" are actually the Battery ECU's Watt-hours number (times 80), so as the battery ages, expect this number to drop, while SOC will still rise to ~95%. This means the watt-hours/SOC will slowly lessen. The battery ECU constantly calculates how the battery ages and produces a Loss of Capacity Coefficient, which will be available on LEAFSCAN.

-Phil
Easily Learn Electricity HERE! - - - - Website: http://evseupgrade.com/ - - - - Like us on Facebook: EVSE Upgrade

User avatar
Ingineer
Posts: 2741
Joined: Fri Oct 15, 2010 1:09 pm
Delivery Date: 13 Jul 2011
Leaf Number: 6969
Location: Berkeley, California
Contact: Website

Re: Real SOC (State of Charge) - Information

Mon Mar 19, 2012 2:00 am

Based on suggestion, I may add an expanded SOC variable that actually runs from 0% to 100% rather than 2% to 95%. The roughly 7% gap is what Nissan decided should not be used for longest life on the battery pack. Last time I checked, my Leaf was reporting 67.568 amp-hours full capacity.

-Phil
Easily Learn Electricity HERE! - - - - Website: http://evseupgrade.com/ - - - - Like us on Facebook: EVSE Upgrade

User avatar
TonyWilliams
Posts: 10085
Joined: Sat Feb 19, 2011 1:48 am
Location: San Diego
Contact: Website

Re: Real SOC (State of Charge) - Information

Mon Mar 19, 2012 2:04 am

Ingineer wrote:Based on suggestion, I may add an expanded SOC variable that actually runs from 0% to 100% rather than 2% to 95%. The roughly 7% gap is what Nissan decided should not be used for longest life on the battery pack. Last time I checked, my Leaf was reporting 67.568 amp-hours full capacity.

-Phil


I think that is wise. Otherwise, it will confuse some people.

Then, we can see the battery at 100% every charge (+/-), and watch the Gid % drop over time. With the two pieces of data, you'll have a good understanding of what you have 100% of.

I think it would be a bit messy to have 88% Gid, and 94% SOC to be a fully charged battery.

Will the LEAFSCAN include the Gid, so I don't need two boxes?

LEAFfan
Posts: 4828
Joined: Fri Apr 23, 2010 6:08 pm
Delivery Date: 08 Jun 2011
Leaf Number: 1855
Location: Phoenix Area

Re: Real SOC (State of Charge) - Information

Mon Mar 19, 2012 2:10 am

Ingineer wrote:The reported SOC usable range seems to be from about 95% (fully charged) to 2% when the battery main contactor opens up and disconnects the pack. The first low battery warning occurs at around 18%, and the second one at around 9%. If I remember correctly, Tourtle mode comes on at about 5%, and begins limiting power. At about 2%, you are totally dead.
-Phil


Mine shows LBW at 17.4% every time, VLBW at 8.5% every time, and Turtle varies between 2.4% and 1.4%. When I drove fast, it was 2.4, but when I drove slowly Turtle happened always at 1.4.
2013 LEAF SV Del. 2/28/13
2013 LEAF World Record for Most Miles Driven On One Charge-188 miles/8.8 m/kW h
4.8 kW DC PV ($ .91/W fully installed)/ Dec., 2010

User avatar
Ingineer
Posts: 2741
Joined: Fri Oct 15, 2010 1:09 pm
Delivery Date: 13 Jul 2011
Leaf Number: 6969
Location: Berkeley, California
Contact: Website

Re: Real SOC (State of Charge) - Information

Mon Mar 19, 2012 3:21 am

LEAFfan wrote:Mine shows LBW at 17.4% every time, VLBW at 8.5% every time, and Turtle varies between 2.4% and 1.4%. When I drove fast, it was 2.4, but when I drove slowly Turtle happened always at 1.4.
Where are you getting these SOC values? Again, Gary's box only shows watt-hours, not SOC.

-Phil
Easily Learn Electricity HERE! - - - - Website: http://evseupgrade.com/ - - - - Like us on Facebook: EVSE Upgrade

User avatar
Ingineer
Posts: 2741
Joined: Fri Oct 15, 2010 1:09 pm
Delivery Date: 13 Jul 2011
Leaf Number: 6969
Location: Berkeley, California
Contact: Website

Re: Real SOC (State of Charge) - Information

Mon Mar 19, 2012 3:22 am

TonyWilliams wrote:Will the LEAFSCAN include the Gid, so I don't need two boxes?
Yes, I can add "Gids" and also the real watt-hours number (gids times 80).

-Phil
Easily Learn Electricity HERE! - - - - Website: http://evseupgrade.com/ - - - - Like us on Facebook: EVSE Upgrade

User avatar
TomT
Posts: 10611
Joined: Sun Aug 08, 2010 12:09 pm
Delivery Date: 01 Mar 2011
Leaf Number: 000360
Location: California, now Georgia
Contact: Website

Re: Real SOC (State of Charge) - Information

Mon Mar 19, 2012 8:01 am

I actually prefer this since, having used Gary's meter for a while now, I find the idea of knowing how much actual charge is in the battery more useful to me for on-going range planning than a scaled percentage of an unknown and changing capacity.

Ingineer wrote:
TonyWilliams wrote:Will the LEAFSCAN include the Gid, so I don't need two boxes?
Yes, I can add "Gids" and also the real watt-hours number (gids times 80).
59,991 miles/12 bars/289 Gids/68.54 AHr/101% SOH/101.64% Hx 7May15 w/ new Lizard (barely made the warranty).
71,770 miles/12 bars/256 Gids/59.04 AHr/88% SOH/87.92% Hx 3Mar16 at lease return.

Now driving a 2016 Volt Premier.

User avatar
garygid
Gold Member
Posts: 12451
Joined: Wed Apr 21, 2010 8:10 am
Delivery Date: 29 Mar 2011
Leaf Number: 000855
Location: Laguna Hills, Orange Co, CA

Re: Real SOC (State of Charge) - Information

Mon Mar 19, 2012 8:28 am

To display an approximation of Usable energy, the GID-Meter (SOC-Meter) displays "GIDs/281" as a percentage, with one decimal: 99.7 for 280.

Having a value that always shows 95% when "Full" is misleading, because the top 5% is not usable.

If the "fuel" value shown always goes to 100%, even after the battery loses capacity, that is also misleading for calculating range. If the battery has lost 7.6%, I would want my "full" fuel gauge to show 92.4% (percentage of New-Battery usable "fuel", or energy).

The GIDs might be derived from 80 Wh increments, but the GIDs at the top disappear more quickly, and those at the bottom will occasionally disappear much more quickly, so, at times, like just before the more-rapid decline, the GIDs do NOT do a good job of indicating the remaining usable energy. I suspect the GID value is "adjusted" downward when any cell-pair's voltage drops "early".

The "real" SOC, as a percent of the whole, but unusable and possibly diminished, battery capacity is not useful for most driving purposes, certainly not for estimating Range.

Yes, maybe a 100% (or other constant value) display indicating that the diminished-capacity battery is "as full as it is going to get" is useful for the car during charging, but not really useful while driving, or for planning to drive.

A MUCH more useful figure would be the Pack's usable-energy Capacity as a percentage of New-Battery (and in kWh). Right now, Nissan "hides" that dapacity-loss information until 15% is gone - MUCH too late to modify usage habits to better preserve the Pack Capacity.

IMO, Gary
See SOC/GID-Meter and CAN-Do Info
2011 LEAF, sold in 2015
2010 Prius, 2014 silver Tesla S
Nissan EVSE, mod to 240/120v 16A
PU: SDG&E
Solar PV: 33 x 225W -> 7 kW max AC
To Sell: X-treme 5000Li EV motorcycle

Return to “Engineering”