Conflicting Info on Range and Energy Stored in Battery

[evnow]

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)

I've a lot of data to prove that gids are definitely not linear w.r.t. m/kWh. Between the two I believe in m/kWh more (even though Phil thinks Gids should be more reliable) - mainly because I've observed that Gids go down rather fast in the beginning.

But, I've seen that Gids are fairly linear when it comes to starting at 80% charge.

BTW, your "Actual range" is really another estimated range. Unless you run till turtle, it isn't actual.

 

[jkirkebo]

Did the first portion of my test:

Charged to 100% (269 gids = 95.7%); temperature 50 degrees in AM

Here's something you can try to see if you can get more than 269 gids:

I assume you have a 80% timer set, and use the timer override button to charge to 100% ?
Then set the car for 100% charging in the afternoon, so it will sit a few hours at 100% before you use it in the morning.
When you wake up, go out to the car and note the number of gids (I assume 269). Then push the timer override button again. Go inside and have breakfast. Then check the car again to see if you get more gids.

The two last times I did this my gids increased from 279 to 282 both times.

 

[surfingslovak]

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%.

Yes, understood, and I'm sorry for not being clearer. I didn't have much time last night. Note that although I did not say that Gids were a measure of SOC, hopefully we can agree that there is some correlation between the two. By extension, 269 Gids would correspond to a high SOC and 25 Gids would correlate with a low SOC. As you know, we have noticed a discrepancy between energy flowing into and out of the battery on a per Gid basis. If we assume that this discrepancy is attributable to heat losses, then higher internal battery resistance would be an important factor. Since the internal resistance curve is typically shaped like a bathtub, we should see disproportionally larger losses at each end of the SOC range. This would then translate to nonlinearity in the energy per Gid plot.

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

Stoaty, I gave it some more thought, and the results are a bit more favorable than originally assumed. Please correct me if I misunderstood something.

Begin: 269 Gids
End: 154 Gids
Usable: 265 Gids
Consumed: 43.4%
Trip: 40.4 miles
MPK: 5.8 m/kWh
Elev change: ~ 1500 feet
Passengers: 1
Cargo: None

Energy expended: 6.96 kWh
Energy lost due to elevation change: ~ 1 kWh
Projected usable energy: 8 kWh/.434 = 18.5 kWh

Note that if you lost 1.5 kWh due to elevation change, then this would translate to 19.6 kWh projected total usable battery capacity, which is not all that far from the 21 kWh we typically use.

 

[Stoaty]

Stoaty, I gave it some more thought, and the results are a bit more favorable than originally assumed. Please correct me if I misunderstood something.

Begin: 269 Gids
End: 154 Gids
Usable: 265 Gids
Consumed: 43.4%
Trip: 40.4 miles
MPK: 5.8 m/kWh
Elev change: ~ 1500 feet
Passengers: 1
Cargo: None

Energy expended: 6.96 kWh
Energy lost due to elevation change: ~ 1 kWh
Projected usable energy: 8 kWh/.434 = 18.5 kWh

Note that if you lost 1.5 kWh due to elevation change, then this would translate to 19.6 kWh projected total usable battery capacity, which is not all that far from the 21 kWh we typically use.

I don't see how you can add 1 kWh for elevation. That is accounted for in the 5.8 m/kWh... unless that figure is really screwy, it means that I traveled 5.8 miles for every kWh used. We can't throw in extra unless the 5.8 m/kWh is a meaningless number.

 

[Stoaty]

OK, here is the additional data from Day 2 of my test. Rather than separating the days, I am going to calculate the overall energy usage and mileage. Didn't drive down to turtle, but got quite a bit lower and got some interesting data:

Total miles traveled in 2 days - 82
Ending percentage from gid-o-meter - 22.7%
Miles per kWh = 6.0 from center console (approximately 5.9 from dash)

Predicted range from this data (if remaining gids are linear and car stops at 4 gids):

(95.7% - 4/281%) * 82 miles/(95.7%-22.7%) = (95.7-1.4) * (82/73) = 94.3 percent * 1.123 miles/percent

= 105.9 miles

Available charge from battery (if miles per kWh is correct and remaining gids are linear) = 105.9 miles / 5.9 miles per kWh = 17.95 kWh

Comments:

1) The predicted range has increased considerably (to my surprise) from 93 miles to 106 miles, and could potentially increase further if I drove all the way to turtle.
2) Gids appeared fairly linear until I got down to around 30-32%, then they went down VERY slowly.
3) Non-linearity was quite evident, with the days usage as follows:

Day 1: .988 miles per percent change on gid-o-meter
Day 2: 41.6 miles / 32.1 percent = 1.30 miles per percent

Note: I made a slight error in the mileage for day 1, which would probably increase it to about 1.008 and decrease day 2 to about 1.28, but I was to lazy to go back and recalculate for this small a deviation.

Net result is that day 2 has a 30% increase in miles/percent over day 1, quite a dramatic difference.
Temperature, speed, etc. were very close both days. The lack of full regen at 80-100% would be an unlikely explanation, because my drive starts out with 2 miles on surface streets followed by a 1000 foot climb over about 6-7 miles on the freeway. In other words, I wouldn't have much opportunity to use regen before getting down below 80%.

4) To get true range, it appears you DO have to drive to VLB or turtle... who knows how much further that 22.7% would get me. The gids might get weaker again, or stay strong until the end.

Conclusion: "All Gids are created equal, but some are more equal than others" (George Orwell)

 

[TonyWilliams]

Conclusion: "All Gids are created equal, but some are more equal than others" (George Orwell)

Bravo. I guess I should trust, but verify, my Gids (Ronald Reagan).

 

[Stoaty]

I repeated the test I did about 7 months ago (results 2 posts above this one in same thread):

Start (Full Charge) - 255 Gids
Work (20.2 miles) - 195 Gids
Home (40.0 miles) - 152 Gids
Work (60.2 miles) - 81 Gids
Lunch trip (69.6 miles) - 69 Gids (increased to 75 Gids when car turned on 6 hours later)
Part way home (73.0 miles) - 64 Gids (22.7% - got 82 miles previously from full charge to 22.7% Gids)
Part way home (82.0 miles) - 49 Gids (LBW, 17.4% Gids)
Home ( 89.3 miles) - 44 Gids (15.6% Gids; long downhill descent to get home uses only 5 Gids for 7 miles)

Temperatures were a bit warmer for this test (70 degrees and 5 Temp bars to start, high at work around 90 degrees F.), driving conditions were quite similar, perhaps a bit more stop and go on the freeway than usual which may have hurt my range a bit.

Range to 64 Gids - 73 miles
Range to 64 Gids 7 months ago - 82 miles

Calculated range loss to 64 Gids compared to 7 months ago - 11%

Predicted range from this data (if gids are linear and car stops at 4 gids): (90.7% - 4/281%) * 89.2 miles/(90.7%-15.6%) =

(90.7-1.4) * 89.2/75 = 89.3 percent * 1.189 miles/percent = 106.2 miles (granted, not bad since there is a 1450 foot elevation gain and loss during the round trip)

Before anyone jumps up and down about different temperatures, etc., I will be repeating the test in a few months when it is cooler to see if there is any difference. While the range loss to 64 Gids appears significant, the predicted range to turtle is almost exactly the same as that done 7 months ago.

Conclusion: without driving all the way to turtle, it appears that Gids are highly unreliable as a predictor of how much range is left. The range doesn't appear to have changed much, but the Gids certainly have!