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azbill

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Your bio says you are an engineer. This should all be second nature to you.
This is why I tried to make it simple for non-engineers. The average person only cares about how many minutes they need to charge to get to the next charger. If I want maximum mile/kw or minimum kw/mile, then I would not get a big truck like Rivian or Hummer, I would get a small 2 seater. But that small 2 seater will have a much smaller battery and thus charge at a slower rate, but will not necessarily give me better time to add 100 miles. It could take more, less or the same time to add those miles.

Many car makers are now advertising X miles in Y minutes, rather than charging rate. And yes this assumes the maximum charging power is avialable, but we see the world moving to the CCS limits. Rivian is now stating 140 miles in 20 minutes, GM has stated 100 miles in 10 minutes for Hummer and 100 miles in 30 minutes for the Bolt. I like this metric because it is simple, and yes I do understand if I use a low power CCS at 50KW that goes out the window and is not achievable.

My baseline for comparison will be if I take a long trip along freeways, which have 350KW EA chargers along the way, which vehicle will provide the minimum minutes I will need to charge.
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ajdelange

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This is why I tried to make it simple for non-engineers.
A noble goal for sure but I am not convinced it is possible.


My baseline for comparison will be if I take a long trip along freeways, which have 350KW EA chargers along the way, which vehicle will provide the minimum minutes I will need to charge.
And I keep pointing out that it is trivial: the one with the higher MPGe rating which is on the Monroney sticker for all to see. Whether the average consumer is capable of appreciating that a car with double MPGe will charge, on average, twice as fast as another is the remaining question.
 

DucRider

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And I keep pointing out that it is trivial: the one with the higher MPGe rating which is on the Monroney sticker for all to see. Whether the average consumer is capable of appreciating that a car with double MPGe will charge, on average, twice as fast as another is the remaining question.
MPGe is completely unrelated to charge speed and no correlation exists.
By your logic the consumer could conclude that the Bolt (118 MPGe) would charge twice as fast as the Hummer (~55 MPGe). But in terms of range per hour of charging, the Hummer can charge 3 times as fast.
MPGe simply measures how efficiently a vehicle uses the energy once it is "on board".

The Bolt, Kona EV, and Model Y all have essentially the same MPGe (118, 120, 121). Under your premise they would all charge at the same rate, but they are vastly different.
If you plugged them into a 50 kW charger, times would indeed be pretty much the same in terms of miles gained per hour. If you plugged into a 100 kWh charger, the Bolt would not improve from the the 50 kW charger, but the Kona would get about a 50% bump and the Model Y would go to 2X. The Model Y can charge much faster still on a V3 Supercharger.
 

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None of the above. It is based on the "facts" that the truck will consume about 450 Wh/mi (the actual number will be based on EPA testing - 450 is my guess as to what that number will be) and that, evidently, the charger will, in a typical cycle, deliver an average power of 189 kW. Thus in 20 minutes it can load 63 kWh useable charge into the vehicle. 63 kWh divided by 0.450 kW/mi = 140 mi/hr. It represents a nominal number which you can use for planning purposes just as the first quote suggests.
Agreed and that was my point. It is just a nominal number and real world circumstances will affect it.
 

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“A noble goal for sure but I am not convinced it is possible.”

Dude, literally every time you say stuff like this, all I can picture is Tywin Lannister (but with an engineering degree) talking about filthy peasants
 

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azbill

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MPGe is completely unrelated to charge speed and no correlation exists.
By your logic the consumer could conclude that the Bolt (118 MPGe) would charge twice as fast as the Hummer (~55 MPGe). But in terms of range per hour of charging, the Hummer can charge 3 times as fast.
MPGe simply measures how efficiently a vehicle uses the energy once it is "on board".

The Bolt, Kona EV, and Model Y all have essentially the same MPGe (118, 120, 121). Under your premise they would all charge at the same rate, but they are vastly different.
If you plugged them into a 50 kW charger, times would indeed be pretty much the same in terms of miles gained per hour. If you plugged into a 100 kWh charger, the Bolt would not improve from the the 50 kW charger, but the Kona would get about a 50% bump and the Model Y would go to 2X. The Model Y can charge much faster still on a V3 Supercharger.
Completely agree @DucRider. In todays world cars are compared by MPG because gas is considered expensive and people care about the cost to get to the destination, not the waiting time to fill up. Whether I have a 10 gallon tank or a 40 gallon tank, the time to fill it up is a few minutes. The overhead of inserting the credit card, selecting the grade and removing/replacing the gas cap make the difference trivial between 10 or 40 gallons. With an EV it is very different, the time to fill up can be dramatically longer, which creates aggrivation for the user.

I have a reservation for the Rivian and one for the Hummer, as well as currently owning a Bolt. It takes me 30 minutes to add 90-100 miles on the Bolt, Rivian will do the same in 15 minutes and the Hummer in 10 minutes. But of course the Bolt is way more efficient (MPGe) and uses less battery to get there. But I do not care about how many electrons I use, I prioritze time over cost of the charge.
 

ajdelange

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MPGe is completely unrelated to charge speed and no correlation exists.
The correlation coefficient is 1 (completely correlated). Try to understand this as until you do you will continue to mislead yourself (and, more to my concern, others).


By your logic the consumer could conclude that the Bolt (118 MPGe) would charge twice as fast as the Hummer (~55 MPGe).
Absolutely correct. Just as with an ICE car. Let's use gallons instead of miles per gallon. Lets say the Hummer gets 5.9 miles per gallon and the Chevy 11.8 miles per gallon (ridiculous numbers but the idea is to get you clear on the concept). You stop at a gas station and need to take on enough fuel to go 118 miles to home (where gas prices are cheaper so you don't want to top off here). The Chevy takes you 11.8 miles per gallon so you need 118/11.8 = 10 gal. If the pump delivers 10 gpm, it takes 1 minute to fuel up. The Hummer's mileage is half: you can only go 5.9 miles on a gallon of gas so you need 118/5.9 = 20 gal. A pump that delivers 10 gpm will take 2 minutes to fill.

But in terms of range per hour of charging, the Hummer can charge 3 times as fast.
Staying with the gasoline analogy the Hummer can only fill faster if it is filled by a pump that has more capacity than the pump that fills the Chevy. And it may also be true that the fill pipe in the Chevy cannot accept a flow rate faster than 10 gpm so that it is impossible to take on gasoline at the same rate as the Hummer.



MPGe simply measures how efficiently a vehicle uses the energy once it is "on board".
And as my and a couple of other peoples' posts point out this is the vehicle parameter than determines the required time to take on a charge sufficient for a specified number of miles given the charging equipment available. Of course the vehicles charging program is important too. So I'll put it here again: charge_time = miles_to_be_added*kWh_per_mile/vehicle_average_charge_rate.

A gallon of gas contains a certain amount of available energy. MPGe is a proxy for the reciprocal of kWh/mi. It represents an, apparently failed, attempt to explain this all to lay people.

I again encourage you to try to get your head around this. It ain't rocket science.



The Bolt, Kona EV, and Model Y all have essentially the same MPGe (118, 120, 121). Under your premise they would all charge at the same rate, but they are vastly different.
If you plugged them into a 50 kW charger, times would indeed be pretty much the same in terms of miles gained per hour.
Yep. Isn't that what we want to know?




If you plugged into a 100 kWh charger, the Bolt would not improve from the the 50 kW charger, but the Kona would get about a 50% bump and the Model Y would go to 2X. The Model Y can charge much faster still on a V3 Supercharger.
All correct per the model. They all require about the same energy to go 100 miles. The time to charge is that amount of energy divided by the rate at which it is supplied. Thus as I mentioned before once a driver knows his consumption he can estimate his charging time by dividing by the rate hos car can take energy from the charger he is contemplating using.
 
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azbill

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Curious as to what kind of engineer you are. I mean which discipline.
I have an EE degree, and have spent my career designing flight control systems for aircraft.
 

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The correlation coefficient is 1 (completely correlated). Try to understand this as until you do you will continue to mislead yourself (and, more to my concern, others).
A Bolt (118 MPGe) that plugs into a 350 kW CCS unit will not charge as fast (miles per minute) as a Kone AV (121 MPGe), Jaguar i Pace (76 MPGe), Audi e tron (78 MPGe), Mach-e (100 MPGe).

Please explain the correlation and how a consumer can look at MPGe and calculate how many miles per minute they will get when charging either at home or at a DCFC.

Granted MPGE will give you efficiency, but is only one piece of the miles per minute equation. Without the other pieces of information, no conclusion can be reached.
 

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Gshenderson

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Now it is apparent to me after explaining this dozens of times in this and Tesla forums and the results of a study posted here that the level of math it requires to understand what I have written in the previous paragraphs far exceeds the abililities of the average American to understand.
Perhaps it’s because you’re not doing an effective job of explaining things in your diatribes. Or it could also be that your tone tends to be that of an arrogant prick so people just don’t read what you write.

Sorry Professor AJ, carry on...
 

ajdelange

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And as my and a couple of other peoples' posts point out this is the vehicle parameter than determines the required time to take on a charge sufficient for a specified number of miles given the charging equipment available. Of course the vehicles charging program is important too. So I'll put it here again: charge_time = miles_to_be_added*kWh_per_mile/vehicle_average_charge_rate.
Please explain the correlation and how a consumer can look at MPGe and calculate how many miles per minute they will get when charging either at home or at a DCFC.
Sure. It's plain from previous posts but as it appears you don't read them completely I'll just repeat and then amplify a bit.

charge_time = miles_to_be_added*kWh_per_mile/vehicle_average_charge_rate.
Gasoline contains energy. As far as the EPA is concerned a gallon of it contains 33.7 kWh. Ar least that's apparently the number EPA uses in MPGe calculations. Thus a car that has a consumption of 100 MPGe goes 100 miles on a a gallon equivalent or 33.7 kWh and uses, thus, .337 kWh to go a mile. The time to charge 100 miles of range is thus 100*.337/rate. At home it's simple as the driver chooses the charging rate. If I have Level 2 going full bore (11.5 kW) the time to add 100 mi is the energy to be added, 100*.337 = 33.7 kWh divided by the 11.5 kW the charger delivers: 33.7/.5 = 2.93 hr.

We could obviously write the formula time = miles_to_be_added*(33.7/MPGe)/charge_rate from which it is clear that time to charge and MPGE are completely correlated. If we plug in 75 MPGe (representative of the Rivians anticipated consumption of 450 Wh/mi.) we get 3.9 hrs required to add that same 100 miles. I just can't see how you fail to understand this most simple of cases.

Now when you go to DC fast charging the picture is complicated by the fact that chargers come in different sizes and different cars take different amounts of power from the same size charger depending on things that I have carefully spelled out in previous posts. This means that the denominator, charge_rate, can vary. In previous posts I have pointed out that one soon learns his car's charging behaviour e.g. I know I can expect about 90 kW from a Tesla 150 kW charger and that tells him what to use in planning.

Granted MPGE will give you efficiency,
For starters I deprecate MPGe. It is much easier to use Wh/mi. Second, it is probably not a good idea to think of these measures as a measure of efficiency (a Rivian at 450 Wh/mi may well be more efficient than a pre Raven X at 337) but rather as the amount of energy required to move the vehicle. A bigger vehicle will take more and obviously, ceteris paribus, take longer to charge.

but is only one piece of the miles per minute equation. Without the other pieces of information, no conclusion can be reached.
Duh!
 

ajdelange

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Perhaps it’s because you’re not doing an effective job of explaining things in your diatribes.
Well that must be it because the science is certainly simple enough. That covers the forum but with respect to the broader problem of widening BEV acceptance we must "Consider the intelligence of the average American and then ponder that half the population is dumber than that".
 
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DucRider

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Sure. It's plain from previous posts but as it appears you don't read them completely I'll just repeat and then amplify a bit.
You have yet to explain how MPGe (or Wh/mi or mi/kWh) can, in and of themselves, be a one to one correlation to miles per minute charging without taking into account the speed of the charger and the max rate the car can accept.
You stated that a vehicle with 2x MPGe would charge 2X miles per minute. I've pointed out many examples where that is not true.
There is no way you can figure miles per minute solely by MPGe, or even relative charge speed. More info is needed.

If all I tell you is the Yamazuka GT3s gets 132 MPGe, and the Truckster QWZ is rated at 64 MPGe, can you tell me which one gets the most miles per minute (or hour) charging? Either at home on L2 or at a DCFC on the road?
Whether the average consumer is capable of appreciating that a car with double MPGe will charge, on average, twice as fast as another is the remaining question.
 

mindstormsguy

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You have yet to explain how MPGe (or Wh/mi or mi/kWh) can, in and of themselves, be a one to one correlation to miles per minute charging without taking into account the speed of the charger and the max rate the car can accept.
You stated that a vehicle with 2x MPGe would charge 2X miles per minute. I've pointed out many examples where that is not true.
There is no way you can figure miles per minute solely by MPGe, or even relative charge speed. More info is needed.

If all I tell you is the Yamazuka GT3s gets 132 MPGe, and the Truckster QWZ is rated at 64 MPGe, can you tell me which one gets the most miles per minute (or hour) charging? Either at home on L2 or at a DCFC on the road?
Do you have an EV? If you do , you will probably know that 50kW chargers are by far the most common DCFC. For as long as this is the case, MPGe is going to be a very good indication of charge speed.
And heck, one day when every car has 350kW charging capability and 350kW charging stations are everywhere, guess what’s going to be the most critical indicator of practical charging speed? Yup. MPGe.

How many people know the flow rate of gas pumps in gallons per minute? Probably close to zero. Why? Because how much time you spend fueling a car is more a factor of the fuel efficiency (and the size of the tank). It’s the same here.
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