Calculating usable battery capacity using Carwings...

[RegGuheert]

Something occurred today which makes me think that under specific condiitions it is possible to calculate battery capacity directly from Carwings and the lifetime efficiency number on the main dash display.

Here's my story:

On March 16, we purchased a 2011 demo vehicle with 2011 miles on it. Typically we see GOM numbers of about 100 miles after a charge to 100% and about 80 miles after a charge to 80%. Yesterday was the first time we have ever deeply discharged the battery on our Leaf. I decided to not recharge between trips into town and had 3 bars showing and 20 on the GOM when I parked in the garage. After plugging into 120V for 100% charging, Carwings showed 2 bars, 18 miles and 16 hours to a full charge. The interesting part came this morning when I looked at Carwings: It predicted only 67 miles of range with 12 bars and charging complete! :shock:

After fully planning my assault on the dealership and composing a long post on TickTock's capacity thread, a cooler head started to prevail. Was the capacity of the car really only 2/3 of what I had previously thought? How to tell? Here are my rough estimations:

- How much of the battery capacity was left when I had arrived home yesterday? Three bars driving and two bars charging indicates 29 to 32%. Let's use 30%.
- How far had I driven yesterday? I didn't measure it but it was likely around 50 miles. Entirely reasonable for a 50% discharge with efficiency shown as 4.6 miles/kWh.
- How much energy was put into the battery overnight? 21.35 kWh from the wall in 14 hours. Assuming an 80% charger efficiency, that indicates 17.1 kW went into the battery. Again, entirely reasonable.

So where did the 67 miles shown on Carwings come from?? Then it hit me: The long-term efficiency shown on the main dash of our car (3.3 miles/kWh) is MUCH lower than what we have achieved since we purchased the car (4.6 miles/kWh). I suspect no one else here has such a large discrepancy between these two numbers! Anyway, it occurred to me that Carwings might be calculating the range as battery usable capacity times long-term efficiency.

Using that assumption, I calculate the usable battery capacity of our Leaf to be:
67 miles / 3.3 miles/kWh = 20.3 kWh

That number seems entirely reasonable and seems to match the range and recharge capacity that the car seems to demonstrate.

So does Carwings ALWAYS show this number? Absolutely not! After I got into the car and turned on accessories, the GOM showed 101 miles, as usual. Looking at Carwings after that event, it now shows 100 miles of range. I also do not recall seeing such a low number on Carwings before (although it is possible I just missed it). So my current theory is that Carwings reports this way only following a deep discharge (two bars or fewer showing at the beginning of charging).

So does this match the capacity which other Leaf owners have calculated for their batteries? I don't know, but if some of you would run the following test and post your results along with what you believe the true capacity of you battery to be along with how your other capacity was determined (gids, 100% to dead range with efficiency, etc.), then I think we can find out.

Proposed procedure to determine your battery capacity from Carwings:

1) Run you battery down to 2 bars or less.
2) Before shutting off your car record the long term efficiency reported by your car. It is on the main display behind the steering wheel. You may need to cycle through the different screens for it to show up.
3) Charge your car to 100%. I started with a scheduled charge but the schedule ended before charging completed and I completed charging by overriding the scheduler. It didn't seem to affect the range reported by Carwings.
4) Use Carwings to obtain the reported range after your car has finished charging to 100%. Be sure to do this BEFORE turning on the car!
5) Calculate your battery usable capacity by dividing the range obtained in step 4) by the efficiency obtained in step 2).
6) Let us know what you got and how closely that matches your expectations. I am particularly interested to see if outliers like TickTock see agreement with their gids and other calcs.

Thoughts?

 

[lpickup]

One flaw with this:

2) Before shutting off your car record the long term efficiency reported by your car. It is on the main display behind the steering wheel. You may need to cycle through the different screens for it to show up.

This is not necessarily long term efficiency. I reset it once a month (actually I did it accidentally about a week ago, meaning to reset my trip odometer). So for me it's only about a week old.

Besides, CARWINGS has its own efficiency data that it's more likely using that having the car send that info from the dash. Who knows what it's really doing, but I would start by checking out all the data within CARWINGS itself to see if you can make any sense of where it's getting its figures from. You don't seem to have really accurate data from yesterday, but is it possible that you actually had poor efficiency yesterday? I usually reset the center console efficiency monitor daily (or at least just before I charge) to get a short-term efficiency reading.

 

[RegGuheert]

This is not necessarily long term efficiency. I reset it once a month (actually I did it accidentally about a week ago, meaning to reset my trip odometer). So for me it's only about a week old.

O.K. I didn't know it was resettable. Regardless, it certainly appears that it may have used this number.

Besides, CARWINGS has its own efficiency data that it's more likely using that having the car send that info from the dash. Who knows what it's really doing, but I would start by checking out all the data within CARWINGS itself to see if you can make any sense of where it's getting its figures from.

Here's the thing: The Carwings account was transferred to us when we purchased the car, so all the old data from the dealer is gone. That doesn't mean it doesn't use it, bit I doubt it. Good suggestion, though. I will dig around to see if I can find any numbers in there that could fit.

You don't seem to have really accurate data from yesterday, but is it possible that you actually had poor efficiency yesterday? I usually reset the center console efficiency monitor daily (or at least just before I charge) to get a short-term efficiency reading.

Yes, my data yesterday was poor, but nothing else points to possibly a very low battery capacity EXCEPT the Carwings range estimate.

 

[Bassman]

Sounds like your demo car didn't get the update on the firmware. Before the latest update, Carwings always was way lower than the actual cars GOM reading, until you start the car. Then Carwings reads what the car says. With the update, Carwings reads pretty consistent with the cars GOM. Not always exactly, but pretty close.

 

[RegGuheert]

Sounds like your demo car didn't get the update on the firmware. Before the latest update, Carwings always was way lower than the actual cars GOM reading, until you start the car. Then Carwings reads what the car says. With the update, Carwings reads pretty consistent with the cars GOM. Not always exactly, but pretty close.

This car has had all of the updates performed.

 

[edatoakrun]

Something occurred today which makes me think that under specific condiitions it is possible to calculate battery capacity directly from Carwings and the lifetime efficiency number on the main dash display...

Thoughts?

See the thread below, from last Summer. I think CW gives you a far more direct, and perhaps, more precise, method of determining Available battery capacity:

Since all my observations have remained consistent in the seven months since, I believe you can use CW kWh use reports, from drives of 100%, to low battery SOC points, to estimate fairly accurately, available battery capacity, and less precisely, also the level of variation in ABC, due to changes in battery temperature.

According to CW, on this drive I used 18.7 kWh to drive 91.1 miles at average energy economy of 4.9 m/kWh....

Extrapolating from the chart, it appears CW may be saying the 1.7 kWh (8.5% from the chart, of 20.4 total kWh-anyone have a better number?) I had left at or near VLBW implies total available battery capacity of about 20.4 kWh.

So, from the limited info I can gather, looks to me that Carwings may now be accurate as to energy use.

http://www.mynissanleaf.com/viewtopic.php?f=31&t=5423&hilit=+carwings" onclick="window.open(this.href);return false;

 

[RegGuheert]

Besides, CARWINGS has its own efficiency data that it's more likely using that having the car send that info from the dash. Who knows what it's really doing, but I would start by checking out all the data within CARWINGS itself to see if you can make any sense of where it's getting its figures from. You don't seem to have really accurate data from yesterday, but is it possible that you actually had poor efficiency yesterday? I usually reset the center console efficiency monitor daily (or at least just before I charge) to get a short-term efficiency reading.

Just to follow up on this, I dug around in Carwings and here is what I see:

- I drove 52.9 miles yesterday.
- No mention of 3.3 miles/kWh is made.
- Average efficiency is 5.9 miles/kWh.
- Yesterday's efficiency was 5.8 miles/kWh.
- The lowest efficiency reported is 5.1 miles/kWh.

Anyway, I still have no other good guess where the 67 mile estimate could have come from, so I'm sticking with my theory for now. It clearly reads the gids from the car, so I see no reason that it doesn't also read the efficiency from the car.

Since that efficiency setting is resettable, I think a good test of my theory would be to reset it and drive like a bandit to make the reading very low, like 1.0 and see what my test reports. Sounds like fun!

 

[RegGuheert]

CW gives you a far more direct, and perhaps, more precise, method of determining Available battery capacity:

Thanks! I agree that is both more direct and more precise! I will certainly do that when I have a chance.

OTOH, if I can verify this approach, it is easier to perform, particularly if draining below 2 bars is not required. In that case, it could be done whenever you recharge to 100%. I should know after a bit more testing.

 

[TonyWilliams]

With the update, Carwings reads pretty consistent with the cars GOM. Not always exactly, but pretty close.

Does that mean they are equally inaccurate and useless?

 

[RegGuheert]

With the update, Carwings reads pretty consistent with the cars GOM. Not always exactly, but pretty close.

Have you tried it under the conditions I specified? That is the only case where I have seen a large discrepancy.

 

[TonyWilliams]

Assuming an 80% charger efficiency, that indicates 17.1 kW went into the battery. Again, entirely reasonable.

Using that assumption, I calculate the usable battery capacity of our Leaf to be:
67 miles / 3.3 miles/kWh = 20.3 kWh

I personally neither use, nor reference (nor even observe) the GoM or CarWings for anything, so I can't help you there. To me, it seems like a dog chasing his tail.

The 240v / 16 amp (3.3kW charger) pulls about 3.8kW from the wall, therefore is about 85% efficient.

I'm sure you realize that a battery at different temperatures has different capacities, and that includes the non-temperature regulated LEAF battery. I use 1% loss per 4F below 70F from 21kWh, therefore a 30F battery would be 10% lower, or 18.9kWh.

 

[edatoakrun]

With the update, Carwings reads pretty consistent with the cars GOM. Not always exactly, but pretty close.

Does that mean they are equally inaccurate and useless?

Evidence clearly indicates that the GOM, is of limited usefulness.

As to using Carwings, I've got 7,200 miles, never seen the turtle, and never had a range experience, varying from that predicted, as accurately corrected for temperature, and ascent/descent, by using CW available battery capacity and m/kWh data.

How ya doing, yourself, Tony?

 

[TonyWilliams]

How ya doing, yourself, Tony?

Not sure what your angle is, but there's not a single one of the 19 turtle events that were helped (or hindered) by the GoM or CarWings. That's because I do not use them. Lack of use did not cause 19 turtle events, if that's what you're loosely suggesting.

Besides generic testing, the car does not have the range I require, therefore I must push it to its maximum. Neither of the aforementioned tools I have found to be of any value to me in that regard.

I don't quite understand how I fit in your enamoration with CarWings. If it works for you, I'd probably keep using it. Cave men found great value in rocks as tools.

 

[RegGuheert]

I personally neither use, nor reference (nor even observe) the GoM or CarWings for anything, so I can't help you there. To me, it seems like a dog chasing his tail.

I understand why, but I'm a new Leaf owner who is holding out for the LeafScan before purchasing any instrumentation. Still I'm trying to get a handle on what I got for a battery.

The 240v / 16 amp (3.3kW charger) pulls about 3.8kW from the wall, therefore is about 85% efficient.

So 3.3 kW is DC power that is delivered to the battery? I'm charging with the 120-V charger, but I saw about 1.59 kW (IIRC!) coming from the wall. I assume the charger is a power-factor correction circuit followed by a DC-DC converter so it looks like a constant-power load regardless of droop in line voltage. My line droops to 115 V. So should I assume that 1.44 kW DC is delivered to the battery?

I'm sure you realize that a battery at different temperatures has different capacities, and that includes the non-temperature regulated LEAF battery. I use 1% loss per 4F below 70F from 21kWh, therefore a 30F battery would be 10% lower, or 18.9kWh.

Thanks! I knew there was a relationship, but I didn't have any numbers. Does that apply both during charging and discharging? In general, those could be quite different temperatures, so it adds a level of confusion (at least for me...).

 

[edatoakrun]

... Cave men found great value in rocks as tools.

The image just appeared in my mind, of Tony the Caveman picking, up a rock to defend himself from a charging sabre tooth tiger, and pulling out his laboriously constructed chart to calculate the initial angle and direction, to throw the rock.

Too bad Tony the Caveman had that rather significant error, on his chart...

 

[TonyWilliams]

Our generally accepted number is 73% at 120v, but you've got a drop in voltage? Not sure what is normal there.

I'm sure you realize that a battery at different temperatures has different capacities, and that includes the non-temperature regulated LEAF battery. I use 1% loss per 4F below 70F from 21kWh, therefore a 30F battery would be 10% lower, or 18.9kWh.

Thanks! I knew there was a relationship, but I didn't have any numbers. Does that apply both during charging and discharging? In general, those could be quite different temperatures, so it adds a level of confusion (at least for me...).

That data is in the notes at the bottom of the range chart. It is likely to change, as we gather data from LEAFscan.

LEAFscan will have the battery temps.

 

[garygid]

With the tools you have (without a GID-Meter or a LEAFSCAN) it is very difficult to evaluate the Battery Pack capacity. Measuring power at the wall, from LBW or VLBW to "100%" can, with SIGNIFICANT corrections, give you some relative values, but hard to get accurate Pack Capacity numbers.

---------
The Carwings data is not known for its accuracy, however, it MIGHT be improving a bit. Generally, we do not even attempt to use it.

The estimated 20 miles remaining on about a 30% "tank" shows how aggressively you were driving during something like the last 5 minutes (or so): 20 miles to use about 6 kWh, or about 3.3 mi/kWh, not "conservative" driving.

After charging to 100%, using that same "last driving" energy usage, 67 miles for the "full tank" is not unreasonable (20* 100 / 30 = 66.66 miles) as an estimate.

So, the 67 miles is related to the energy "in the tank", but is strongly colored by your recent driving "style".

 

[edatoakrun]

"garygid"
...The Carwings data is not known for its accuracy, however, it MIGHT be improving a bit. Generally, we do not even attempt to use it....

Since you (apparently) never look at CW data, why do you believe it to be inaccurate?

You have a reference tool, that I do not, to determine CW accuracy.

I readily admit, that CW may not give the most accurate data available, but it seems to give very good data, with my LEAF.

I think it's very unfortunate, that, to the best of my knowledge, no one who has a "gid meter", has ever posted updated CW data comparisons, to determine CW accuracy.

 

[RegGuheert]

The estimated 20 miles remaining on about a 30% "tank" shows how aggressively you were driving during something like the last 5 minutes (or so): 20 miles to use about 6 kWh, or about 3.3 mi/kWh, not "conservative" driving.

Nope. That's nowhere close to accurate. For the last 10 minutes of my drive yesterday, I had no one on my tail and I was on the familiar, flat back roads to home. Climate control was off all day since the weather was excellent. Certainly these were the most efficient of the 5.8 mile/kWh day. Certainly over 6 miles/kWh over those last 10 minutes. More likely the GOM was using the 3.3 miles/kWh displayed on the console.

But perhaps you are correct that ratio displayed at the end of the trip is what was used for the range estimation during the charge.

 

[Pipcecil]

I pretty much lost faith in the carwings range estimate during winter time when it would spit out numbers horribly inaccurate. I was regularly seeing 35-38 miles for a full charge on carwings....if that happend I wouldn't make it to work and back (55+ miles), yet I did, with an easy 3 bars left during cool temps (in the 50's). After a few rounds of seeing this in CW when I would pre-heat the car, I just stopped looking at it. The GOM is way more accurate than carwings is and if I had to choose, would shoose the GOM.