Conflicting Info on Range and Energy Stored in Battery

The more I read about range and SOC, the more it seems to me that the various numbers conflict with each other. Here is the data that appears to give conflicting information:

1) Full charge (no change after balancing for several hours then recharging 2 days later) on my Leaf is 269 gids
2) My long-term average over 6700 miles (virtually no variation over time) is 5.7 miles per kWh from the dash
3) My daily commute (measured at same 5.7 miles per kWh) of 45 miles takes very close to 45% on the Gid-o-meter, e.g., starting at 80% SOC, I typically end up very close to 35% SOC.
4) Per Ingineer, each gid is 80 wh
5) The claimed rule of thumb that miles per kWh * 21 gives total range

Predicted range from #5: 120 miles
Actual range from #3: 100 miles (one mile per one percent of charge, good estimate unless gids are highly non-linear)

Energy in my battery when fully charged (per Ingineer) = 269*80/1000 = 21.5 KWh
Energy in my battery apparently available for my use = 100 mile range/5.7 miles per kWh = 17.5 kWh

These numbers seem pretty far apart. Can anyone explain these discrepancies? Do others with a Gid-o-meter see the same discrepancies, or am I an outlier?

Stoaty, good data. Couple of observations: have you driven your Leaf to turtle or at least to the very low battery warning? Extrapolating range is useful, but only to a point. Based on the discussion in the What is a Gid thread, I would expect 8% difference between energy available at the wheels and what's stored in the battery. In your case, this would amount to 19.8 kWh or 112 miles of range from full to turtle. This is not all that far from your range estimate. Note that I have measured between 20.3 to 21 kWh of available energy at the wheels, and have achieved 107 miles of range with 5.1 kWh energy economy. If your true range was only 100 miles, then we are clearly missing something.

The 80 Wh per GID might be close to the energy applied to the battery while charging, I am not sure. However, less than that is actually stored in the battery.

Then, as energy us recovered from the battery, even more energy is lost, so the usable recovered energy is noticably less than 80 Wh per GID.

Yes, GIDs appear to be non-linear, and it is not clear to me exactly how/when they are "created" or "used".

So, that would explain some of your "contradictory" data.

The car's estimates of miles/kWh could also be off a bit.

Stoaty said:

4) Per Ingineer, each gid is 80 wh
5) The claimed rule of thumb that miles per kWh * 21 gives total range

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Ingineer quoted Nissan's published data that a Gid is 80Wh.

Nissan has made many published remarks that don't always add up, or tell the full story.

The 21 multiple rule of thumb will only work with a battery that can provide 21kWh. A cold battery will not come close to that figure.

"garygid"

...The car's estimates of miles/kWh could also be off a bit.

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Or, quite a bit...

garygid said:

The 80 Wh per GID might be close to the energy applied to the battery while charging, I am not sure. However, less than that is actually stored in the battery.

Click to expand...

That's an interesting angle, and the 8% loss figure would be somewhat plausible if it represented the heat dissipated in the battery on the way in and on the way out, plus coulombic inefficiency.

Could be 3% heat going in (110 watts of 3600 when L2 charging),
and perhaps 5% going out at the much higher driving currents.

5.7 miles per kWh sounds quite high to me; my dash reports between 4.2 and 4.3 miles per kWh consistently, which would be 4.3*21=90.3 miles of driving range; so far, that is pretty close to what I get on a day-to-day basis.

I have taken day trips within the metro area of about 82 miles several times and returned home with the GOM claiming 6 miles left or so.

Could it be that the current software update will correct the calculations for the OP and bring the miles per kWh down to something more accurate?

I went back and looked at the latest version of Tony's range chart and made a few corrections which bring his predicted range closer to what I am seeing (again, without driving all the way to VLB, which I should do one of these days):

kWh - 21
miles per kWh - 5.7

Predicted range - 119.7

Corrected for age of battery - 119.7 * .9867 = 118.1

Corrected for temperature of 60 degrees F. = 118.1 * .975 = 115.2

Corrected for elevation gain/loss of 1450 feet: uses extra 1.45 bars for gain, saves 0.725 bars for loss = extra 0.725 bars used

Assuming one bar is 1.4 kWh (from another ancient post), then 0.725 * 1.4 = 1.015 kWh extra used

So 1.015/21 = additional 4.833% correction factor

Final predicted range from Tony's chart = 115.2 * (1-.04833) = 109.6

This is a lot closer to my estimated range of 100 miles for speed/elevation of my daily commute. Perhaps my next test will be to charge to 100% (94% actual SOC), and drive 2 work and back 2 days in a row without charging (90 miles total) and see what percent of charge I have left. I don't want to bother with running it all the way to VLB, although I suppose I could do that after the second day of 90 miles.

PS I still really have to wonder about that 5.7 on the dash.

I don't trust the miles/kWh display that much, but the GIDs X 80 definitely is stored watt-hours. Keep in mind there are a lot more things in the car using energy besides the motor. You have about 200-300 watts of base load for the car to just be "ready".

The watt-hours (GIDs X 80) are calculated by coulomb counting and are corrected for drift. This is that the battery ECU uses for decision-making, and I have a lot of faith in it. The CM (Combination Meter) display is using information from the Battery ECU to calculate kWh/mile, so what do you trust more?

-Phil

Ingineer said:

I don't trust the miles/kWh display that much, but the GIDs X 80 definitely is stored watt-hours. Keep in mind there are a lot more things in the car using energy besides the motor. You have about 200-300 watts of base load for the car to just be "ready".

The watt-hours (GIDs X 80) are calculated by coulomb counting and are corrected for drift. This is that the battery ECU uses for decision-making, and I have a lot of faith in it. The CM (Combination Meter) display is using information from the Battery ECU to calculate kWh/mile, so what do you trust more?

Click to expand...

The base load should be included in the MPK figure. There is an easy way to verify this: turn the car on, and the energy economy figure should start dropping. Note that this will only work if you reset the economy gauge after each full or 80% charge, not when you use it to measure lifetime economy.

I totally agree that some of the energy is getting lost, and we don't have a good grasp where it occurs. The most likely candidate is heat losses in the battery. I too believe that Nissan can count coulombs going in and out of the battery accurately, but they cannot measure the heat and other losses in the battery itself. The odometer, and the energy economy gauge are not perfect, and by no means accurate, but we are looking for a fairly consistent loss of 8%. I believe that it will be difficult to rationalize it by instrument error alone.

surfingslovak said:

The base load should be included in the MPK figure. There is an easy way to verify this: turn the car on, and the energy economy figure should start dropping.

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Yes, it does go down. I've sat in it many times waiting.

Did the first portion of my test:

Charged to 100% (269 gids = 95.7%); temperature 50 degrees in AM
Drove to work and back - 40.4 miles from odometer; temperature 68 degrees when I started the trip home
Miles per kWh = 5.9 from center console (equivalent to about 5.8 from the dash)
Finished with 54.8% charge

Predicted range from this data (if gids are linear and car stops at 4 gids): (95.7% - 4/281%) * 40.4 miles/(95.7%-54.8%) =

(95.7-1.4) * 40.4/40.9 = 94.3 percent * .988 miles/percent = 93.2 miles (granted, not bad since there is a 1450 foot elevation gain and loss during the round trip)

Available charge from battery (if miles per kWh is correct and gids are linear) = 93.2 miles / 5.8 miles per kWh = 16.1 kWh

It seems to me that either:

--the miles per kWh is way off
--the slightly cooler temperature causes my battery to have a much lower number of kWh that can be delivered to the motor

I will update the calculations tomorrow after driving another 40-45 miles to see if the calculated range numbers change; I suspect they won't, but could be surprised if the gids prove to be highly non-linear.

Interesting test.

What I want to know is how many mph do you average to get 5.8 miles kWh? And how do you get that with the elevation change? You must really take your time getting around.

Something seems off to me as well. A usable capacity of 16kwh seems like a better number to me and reflects my experience with the m/kwh not correlating to reality.

Stoaty said:

Did the first portion of my test:
Available charge from battery (if miles per kWh is correct and gids are linear) = 93.2 miles / 5.8 miles per kWh = 16.1 kWh

It seems to me that either:

--the miles per kWh is way off
--the slightly cooler temperature causes my battery to have a much lower number of kWh that can be delivered to the motor.

Click to expand...

EVDrive said:

Something seems off to me as well. A usable capacity of 16kwh seems like a better number to me and reflects my experience with the m/kwh not correlating to reality.

Click to expand...

Interesting data. Quick comment: I believe that you are losing at least 1 kWh due to elevation change. I believe that some Gid nonlinearity was observed at each end of the SOC range, presumably due to increased internal resistance of the battery, and other factors.

EDIT: I'm getting 69 Wh average per Gid expended. This is about 5% lower than what I saw in other samples. Combine that with a lower Gid total, and you are looking at about 10% reduction in usable energy. If you wanted to consider the ideal case, divide 21 kWh by 277 Gids, which roughly represents one cycle from full charge to turtle, and you would get about 75 Wh average per Gid.

EVDrive said:

What I want to know is how many mph do you average to get 5.8 miles kWh? And how do you get that with the elevation change? You must really take your time getting around.

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I drive like an old lady. Seriously, I generally drive about 50-52 MPH on the freeway (which is probably about 13 miles of the 20 mile one way drive). On the surface streets, I drive for the lights, meaning I try to avoid using brake or regen to the maximum extent possible. Speeds vary from 20-40 MPH depending on the distance between lights and my experience of when lights usually turn. Cars often pass me on the surface streets, but I usually catch or pass them waiting for the light to turn green. Most people drive incredibly inefficiently on surface streets, I call their driving pattern "hurry up and wait". I guess I drive like an old lady. :lol: My driving adds about 4 minutes to my commute each way, mostly from the slower speeds on the freeway. I break even on surface streets, because I rarely wait much at the stop lights.

determining range, even with all this great data, still comes down to determining average MPkW and trying to maintain a certain average speed. As Tony has pointed out, using the car's average speed calculator is not reliable, but neither is the one between our ears. How are folks reliable averaging speed? Using a constant speed for tests is great, but in reality it just isn't doable with stop lights, traffic etc. so calculating range based on stored energy and average speed gives a very squishy number in the real world. the only way I've been able to adapt this and reliably predict range is by using the power meter to cap energy usage to 2 to 3 bubbles and breaking gently to help level out the MPkW's, shooting for a target MPkWh, virtually ignoring speed, which means taking the hills in the right lane.

well stated, "Hurry Up And Waite" is the range killer! It's amazing to see how much people get worked up over a few extra average minutes.

Stoaty said:

EVDrive said:

What I want to know is how many mph do you average to get 5.8 miles kWh? And how do you get that with the elevation change? You must really take your time getting around.

Click to expand...

I drive like an old lady. Seriously, I generally drive about 50-52 MPH on the freeway (which is probably about 13 miles of the 20 mile one way drive). On the surface streets, I drive for the lights, meaning I try to avoid using brake or regen to the maximum extent possible. Speeds vary from 20-40 MPH depending on the distance between lights and my experience of when lights usually turn. Cars often pass me on the surface streets, but I usually catch or pass them waiting for the light to turn green. Most people drive incredibly inefficiently on surface streets, I call their driving pattern "hurry up and wait". I guess I drive like an old lady. :lol: My driving adds about 4 minutes to my commute each way, mostly from the slower speeds on the freeway. I break even on surface streets, because I rarely wait much at the stop lights.

Click to expand...

surfingslovak said:

EVDrive said:

Something seems off to me as well. A usable capacity of 16kwh seems like a better number to me and reflects my experience with the m/kwh not correlating to reality.

Click to expand...

Interesting data. Quick comment: I believe that you are losing at least 1 kWh due to elevation change. I believe that some Gid nonlinearity was observed at each end of the SOC range, presumably due to increased internal resistance of the battery, and other factors.

EDIT: I'm getting 69 Wh average per Gid expended. This is about 5% lower than what I saw in other samples. Combine that with a lower Gid total, and you are looking at about 10% reduction in usable energy. If you wanted to consider the ideal case, divide 21 kWh by 277 Gids, which roughly represents one cycle from full charge to turtle, and you would get about 75 Wh average per Gid.

Click to expand...

SOC? Gids are not a measure of SOC as stated previously. As the pack ages SOC would always go up to 100% even if the car had 50% capacity, Gids will drop over time even when the car is charged to 100%.

Thats the best way to get extra range.. drive as if you did not have brakes (no regen either). Works very well with ICE cars also.