Fuel economy units? KWh figure from charger vs. car?

[mkaresh]

We're (finally) upgrading the fuel economy survey on TrueDelta to support electric vehicles. Would people only want to see fuel economy reported in terms of kWh per 100 miles? Or would the option of MPGe also be desirable?

What we're leaning toward is kWh per 100 miles in member's personal logs, but MPGe on the public site, given that few non-owners would be able to make sense out of the former metric.

We're also planning to include a toggle to specify whether the kWh figure comes from the charger or the car's computer, as my understanding is conversion losses tend to be about 15 percent. Will there be a need for this? If people reported figures both ways, we'd need to convert one to the other to make them commensurable. But what percentage might we then assume? (I imagine this could vary by the level of charger, as conversion losses are probably higher with the fast ones.)

Finally, how to handle partial charges. I imagine LEAF owners often don't fully recharge the battery because of time constraints. How might they then track fuel economy? Rely on the trip computer? Or add all of the charges and miles driven between full recharges?

For the latter, owners will initially have to keep track of the partial recharges then add them all up before entering the information. In the next phase we plan to support partial recharges.

Any advice on these questions would be very much appreciated.

 

[HighDesertDriver]

We're (finally) upgrading the fuel economy survey on TrueDelta to support electric vehicles. Would people only want to see fuel economy reported in terms of kWh per 100 miles? Or would the option of MPGe also be desirable?

Everyone here on MNL speaks in terms of miles/kWh, the way the car reports it on the dash and in Carwings. Personally, MPGe is not something that means much to me as a BEV owner.

What we're leaning toward is kWh per 100 miles in member's personal logs, but MPGe on the public site, given that few non-owners would be able to make sense out of the former metric.

We're also planning to include a toggle to specify whether the kWh figure comes from the charger or the car's computer, as my understanding is conversion losses tend to be about 15 percent. Will there be a need for this? If people reported figures both ways, we'd need to convert one to the other to make them commensurable. But what percentage might we then assume? (I imagine this could vary by the level of charger, as conversion losses are probably higher with the fast ones.)

This is a potential trouble area because the different numbers people have access to. You would likely need more than just two choices. As for "conversion losses", they are real but come in two forms, the variable losses incurred when chemically moving electrons in and out of the battery, and the more constant losses (vehicle overhead) to cool the charger. L2 charging is more efficient than L1 because that overhead remains constant. Doubling the amps being drawn from the wall more than doubles the power pushed to the battery.

Finally, how to handle partial charges. I imagine LEAF owners often don't fully recharge the battery because of time constraints. How might they then track fuel economy? Rely on the trip computer? Or add all of the charges and miles driven between full recharges?

MNL has some members that always charge to 100%, some that never go above 80%, and many that opportunity charge for as long as they can wherever the charging is free. The value of their data depends on the level of detail they keep. In my case, it would be easiest to report monthly the number of kWh's used from the wall and the number of miles driven.

For the latter, owners will initially have to keep track of the partial recharges then add them all up before entering the information. In the next phase we plan to support partial recharges.

Any advice on these questions would be very much appreciated.

 

[mkaresh]

Excellent information, thanks!

We'll add a way to specify L1, L2, L3 (an option for some cars).

It sounds like you personally have the amount output by the charger, correct? While other people would have the figure reported by the car. So we will need a way to estimate conversion losses if we want to combine both sorts of figures (unless I'm missing something).

As I see it, losses during regen aren't anissue, since they're not part of the energy acquired externally. Efficient regen comes through in improved fuel efficiency.

 

[Boomer23]

As for mi/kWh, almost all EVs have a display on the dash that should be comparabe to other EVs for in-car measurements. Only a small proportion of EV drivers have an accurate way to measure actual charging energy from the wall source, so a clearly identified in-car reading would be the most universal.

KWh/100 miles, usually measured at the wall power source is well understood by the EV community and the EPA sticker uses such a figure measured at the wall source, because that takes into account the car's overall efficiency, including its onboard charger. I agree that MPGe would be better understood by the average reader.

Partial charges should not be a problem. If an EV driver resets a mi/kWh display at the beginning of each day or each week or month, the partial charges and miles driven will be properly included in the average mi/kWh for that driving time frame or trip.

Interestingly, most drivers will get better energy economy when charging to less than 100% because brake regeneration is not available if the battery is full.

 

[mkaresh]

Thanks, very good to know. We're hoping to make it possible for people to record information however they want to.

On the battery not recharging through regen when it's full--isn't this a physical impossibility. To brake, you must first accelerate, and accelerating must always use more energy than can be recouped when you brake. In a hybrid I can see a potential limitation, but not a full electric with no additional energy source.

 

[Boomer23]

On the battery not recharging through regen when it's full--isn't this a physical impossibility. To brake, you must first accelerate, and accelerating must always use more energy than can be recouped when you brake. In a hybrid I can see a potential limitation, but not a full electric with no additional energy source.

Right, but the BMS (battery management system) limits regeneration until the pack charge is reduced somewhat. At full charge, even if you just floored the A pedal for a mile, you won't get any recharge until you've gone a few miles. The availability of regen is indicated in the LEAF by double circles shown on the main dash power meter. Single circles denote no regen available at that power level, double circles indicate the availability of regen. There are four regen levels indicated on the dash, though it is a continuous quantity, not a stepped one, and the LEAF will slowly release all levels of regen as you start to drain the pack from a full charge down to about 90% as I recall.

Notice this pic of our LEAF's dash on delivery day at the dealer. The car has 11 of 12 bars of charge, perhaps 95% charged. Only three of the four regen circles to the left of the white dot in the "zero" circle have double rings around them, indicating that regen is limited to some percentage of full regen that will be available as the pack charge drops with further usage.

 

[Nekota]

On the battery not recharging through regen when it's full--isn't this a physical impossibility. To brake, you must first accelerate, and accelerating must always use more energy than can be recouped when you brake. In a hybrid I can see a potential limitation, but not a full electric with no additional energy source.

Another source of regen charging is potential energy. If you charge on higher elevation then you add additional charge from the regen when going downhill.

 

[mkaresh]

Right, but the BMS (battery management system) limits regeneration until the pack charge is reduced somewhat. At full charge, even if you just floored the A pedal for a mile, you won't get any recharge until you've gone a few miles. The availability of regen is indicated in the LEAF by double circles shown on the main dash power meter. Single circles denote no regen available at that power level, double circles indicate the availability of regen. There are four regen levels indicated on the dash, though it is a continuous quantity, not a stepped one, and the LEAF will slowly release all levels of regen as you start to drain the pack from a full charge down to about 90% as I recall.

Notice this pic of our LEAF's dash on delivery day at the dealer. The car has 11 of 12 bars of charge, perhaps 95% charged. Only three of the four regen circles to the left of the white dot in the "zero" circle have double rings around them, indicating that regen is limited to some percentage of full regen that will be available as the pack charge drops with further usage.

I might have good news for you--I think you're misreading that gauge (or I'm misreading which part of it you're refrring to). Does that fifth circle ever have a double? I suspect not. Instead, what it's showing you is how hard you can brake and still have the regen system do the braking. If you brake really hard (fifth circle) the regen brakes can't slow the vehicle quickly enough, and it has to rely on the conventional brakes instead.

 

[mkaresh]

On the battery not recharging through regen when it's full--isn't this a physical impossibility. To brake, you must first accelerate, and accelerating must always use more energy than can be recouped when you brake. In a hybrid I can see a potential limitation, but not a full electric with no additional energy source.

Another source of regen charging is potential energy. If you charge on higher elevation then you add additional charge from the regen when going downhill.

I hadn't thought of this one--definitely makes sense. So if you live at the top of a hill, you don't want to fully charge the battery. But who would do something as ecologically unsound as living on top of a hill?

 

[DaveinOlyWA]

i reset the Miles/Kwh and Trip B on the dash daily . Trip A i reset weekly and the Miles/Kwh on the center console i reset monthly. the Dash reading is slightly lower than the center console reading. as i understand it, the dash is the car reading, the console is Carwings. why they are different? dk.

 

[evnow]

On the battery not recharging through regen when it's full--isn't this a physical impossibility. To brake, you must first accelerate, and accelerating must always use more energy than can be recouped when you brake. In a hybrid I can see a potential limitation, but not a full electric with no additional energy source.

Leaf limits regen when the battery is close to full. This is because regen (which recharges the battery) has a limitation on how much kW that can be pumped into the battery when it is nearly full.

Every 10 Gids release one regen circle.

 

[DaveinOlyWA]

On the battery not recharging through regen when it's full--isn't this a physical impossibility. To brake, you must first accelerate, and accelerating must always use more energy than can be recouped when you brake. In a hybrid I can see a potential limitation, but not a full electric with no additional energy source.

Leaf limits regen when the battery is close to full. This is because regen (which recharges the battery) has a limitation on how much kW that can be pumped into the battery when it is nearly full.

Every 10 Gids release one regen circle.

regen is more temp dependent than that. i have seen many times when only 3-4 regen circles were available at SOC way under 87.5 % in winter

 

[HighDesertDriver]

Right, but the BMS (battery management system) limits regeneration until the pack charge is reduced somewhat. At full charge, even if you just floored the A pedal for a mile, you won't get any recharge until you've gone a few miles. --snip--

I might have good news for you--I think you're misreading that gauge (or I'm misreading which part of it you're refrring to). Does that fifth circle ever have a double? I suspect not. Instead, what it's showing you is how hard you can brake and still have the regen system do the braking. If you brake really hard (fifth circle) the regen brakes can't slow the vehicle quickly enough, and it has to rely on the conventional brakes instead.

No, he is quite right. We live on a hill and can roll downhill a couple miles before before leveling off. On those occasional times when we charge to 100%, we pull out of the garage on power and have one double regen bubble showing. Our speed downhill is controlled by regen for maybe 200 yards, after which the bubble goes single and we begin to accelerate as if in neutral.

As suggested by one of the previous posters, you will have the greatest participatation if all the required data can be obtained from the car itself. It is only a guess, but it is probably only a small minority of operators who through meters or monitors know the kWh going to the EVSE at home. Of that group, some charge at unmonitored locations away from home and bias their dashboard data.

 

[Boomer23]

Right, but the BMS (battery management system) limits regeneration until the pack charge is reduced somewhat. At full charge, even if you just floored the A pedal for a mile, you won't get any recharge until you've gone a few miles. The availability of regen is indicated in the LEAF by double circles shown on the main dash power meter. Single circles denote no regen available at that power level, double circles indicate the availability of regen. There are four regen levels indicated on the dash, though it is a continuous quantity, not a stepped one, and the LEAF will slowly release all levels of regen as you start to drain the pack from a full charge down to about 90% as I recall.

Notice this pic of our LEAF's dash on delivery day at the dealer. The car has 11 of 12 bars of charge, perhaps 95% charged. Only three of the four regen circles to the left of the white dot in the "zero" circle have double rings around them, indicating that regen is limited to some percentage of full regen that will be available as the pack charge drops with further usage.

I might have good news for you--I think you're misreading that gauge (or I'm misreading which part of it you're refrring to). Does that fifth circle ever have a double? I suspect not. Instead, what it's showing you is how hard you can brake and still have the regen system do the braking. If you brake really hard (fifth circle) the regen brakes can't slow the vehicle quickly enough, and it has to rely on the conventional brakes instead.

Nope, all of the circles become double once the charge gets used up enough, which happens within the first 5 miles or so.

 

[mkaresh]

Thanks for the correction!

One thing I keep asking for, but haven't seen in any hybrid or electric, is an indication of the percentage of braking being performed by regen. I think this would be very helpful feedback.

 

[dgpcolorado]

Thanks for the correction!

One thing I keep asking for, but haven't seen in any hybrid or electric, is an indication of the percentage of braking being performed by regen. I think this would be very helpful feedback.

While that would be nice it is actually a hard number to calculate.

Be aware, however, that when using A pedal braking all of it is regen. So cars that have enough regen on the A pedal can be driven with almost no use of the brake pedal or friction brakes. If you don't have much experience with EVs the notion of driving with little or no use of the brake pedal takes some getting used to. It is completely different from an ICE car.

As to the original question, I think you will open up a can of worms asking EV owners to report mileage numbers. There are so many variables that the data are hard to compare from one owner to another. For example: it was mentioned upthread, what about those who charge away from home? When I do that, which is rare, I meticulously track the electricity I use and add it to my total from the wall at home. But people who have the ability to measure energy from the wall are very few.

If you just report the car dashboard miles/kWh reading you don't really have the true efficiency of the use of the car. It isn't as simple as correcting the dash measurements by 15% for 240V/16A charging and 25% for 120V/12A charging because there are so many other variables. For example, preheating or precooling while plugged-in will increase electricity use and lower miles/kWh. Charging to less than 100% or 80% is more efficient than charging to a higher SOC because much of the charging overhead losses are fixed but charging slows as the car nears full. Unless one actually measures numbers from the wall, actual miles/kWh will be quite different, and variable, from the miles/kWh reported on the car's dash. And even that reporting depends on how often the meters are reset and whether or not the owner keeps detailed records. I would venture to guess that very few LEAF owners bother to keep records of mileage efficiency readings. Incomplete data will just skew the results and make them meaningless, IMO. (And don't get me started on "Carwings", which depends on pushing the "yes" button on every single trip to have any semblance of validity.)

This begs the question: why do you want to track this information? To compare one EV model to another? To look at seasonal or regional variations in mileage? While those would be worthy goals, trying to get this information from owners in any useful way seems very difficult unless you have a way to vet the data. It is much easier to measure miles per gallon for an ICE car yet how many owners track even those simple-to-obtain numbers?

 

[TonyWilliams]

Yes to everything stated above ^^^^^^^^^^

The regen on a 100% battery is near zero%. On a fully depleted battery, it's greater than zero and less than 100%.

Push the brakes too fast or hard.... Regen goes back to near zero. Hit a big bump that cause an ABS event, little or no regen. Battery too hot from ambient air or frequent DC charging? Restricted regeneration. Battery too cold? Restricted regeneration.

I do not recommend trying to get this info. We have people on hear who will adamantly swear there is one number, though.

On the range chart, I just give it a generic 50%-75% regen. So, the LEAF will consume about 1.5kWh gaining 1000 feet / 300 meters in elevation, and therefore should gain through regen about 50-75% of that while losing 1000 feet / 300 meters.