# Help me understand Wh/mi



## 3V Pilot

Okay, I understand that Wh/mi is the amount of energy it took to drive a certain amount of miles. What I'm trying to figure out is how to relate that to cost per mile or how to compare it to MPG of an ICE car. There is a recent pic of a Model 3 showing 254 Wh/mi. If my electricity cost 12 cents per kWh what math would I need to do to figure out cost per mile? I understand that this number might change based on how I drive and maybe some current owners could help out here, is 254 an average number?

I'm trying to figure all this out because I might switch my electricity to a time of use plan once I get my car. I haven't done it yet because they charge $19 a month to be on the plan, I don't use much electricity right now and rates are not that much better on the plan. I drive about 300 miles a week just back and forth to work, don't know if I'd save more than $19 a month once I start charging this car. I'd like to have a better understanding of how to calculate some of these crazy new electric car numbers. And please keep it simple, after all, I am a gear-head and I've sniffed exhaust fumes for too many years to understand higher math....LOL!

For you math geniuses out there, right now I pay 12 cents per kWh (up to 800kWh then it goes to 13 cents per kWh).
On the TIme of Use Plan I would pay 07 cents per kWh off peak but the on peak rate is 19 cents.

I'd like to know, just based on driving to work and back how much I might save if I changed plans.....


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## BigBri

I could be wrong but it should just be 0.254KWH/M so it'd be 1KW to do 3.9~miles. Sounds about right as I get around 7.5km/KWH in the summer and around 5.7 this time of year in a Leaf. My average this month is 192WH/KM


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## mig

$.12/kWh /(3.9 mi/kWh) = $0.031/mi

300 miles will cost about $9.30 at this rate

$0.07/kWh/(3.9 mi/kWh) = $0.018/mi

300 miles will cost about $5.40
(Barring dumb error on my part)

Yes, 254 Wh probably is an average and real world will vary (but in my experience possibly for the better!)


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## 3V Pilot

Okay, so based on the above math I wouldn't even be making up the $19 a month it would cost me. That is good info and what I was looking for, thanks!

Just one other question though, how do you get from 254 Wh/mi to the fact that it takes 1 kWh for 3.9 miles? I don't understand how that works and would like to be able to figure that out if my average "mileage" is different. Is there any good website or spreadsheet that has a calculator for all these numbers? Something I could just input my average Wh/mi and electric rates that would spit out cost per mile and cost to recharge for X number of miles or any other useful figures.


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## DR61

254 Wh/mi is 1 mi/.254 kWh = 3.94 mi/ kWh


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## 3V Pilot

DR61 said:


> 254 Wh/mi is 1 mi/.254 kWh = 3.94 mi/ kWh


Thank you!.....that is almost easy enough that even I could do it!. Still wondering if someone could come up with a spreadsheet that would crunch all these numbers for me. I know, it's probably not that difficult to accomplish if it's as easy as whats shown above, I'd just like to have something I could plug different numbers into and see how the effect the outcome. Different Wh/mi, different electric rates, different miles driven per month and what it all would cost per mile and per month.


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## Scuffers

there are several, here's one.


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## Kizzy

If it's not clear already, there are 1,000 watthours (wh) in 1 kilowatthour (kWh).

I set up a quick Google sheet for you to calculate costs. Fill in the cells in green.


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## SoFlaModel3

I know you got your answers, but interesting topic. I’ve come to the realization that my costs will go way down each month but never in my mind took it a step further than a high level estimate of about $120/month in savings. 

So right now gas in my area is $2.80/gallon. My car goes ~350 miles on 15 gallons. That’s 23.333 miles per gallon. Finally that’s $0.12/mile.

For electricity in my area we’ll go with the similar $0.12/kWh. If the car uses 254 Wh/mile, then that’s $0.03/mile.

That means each mile costs me 75% less “fuel”.

I currently spend $150/month on gass and was figuring around $30/month for electricity. It looks like $37.50 may be the safer estimate.

Of course early days I may have lead right foot syndrome and it could be worse


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## Dr. J

You could extend the calculation beyond fuel cost to total ownership cost by adding maintenance, depreciation and financing costs. And anything I've left out.


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## Guest

Number instrument cluster shows is not the number you pay for. You pay more.
It also applies to some ICE vehicles that do not measure fuel consumed while stationary.
For example my BMW uses fuel heater, that fuel is not metered. But I still have to buy it.
In case of electric vehicle, you pay at the meter, not battery output.
So there can be more energy used if vehicle is preconditioned.
Also add 10% as charging losses (10% more metered than charged to battery).


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## Dan Detweiler

Bottom line...you're going to spend about 25-30% of what you do now in fuel. Then you can start adding in ancillary stuff like oil changes, brake wear, etc.

Dan


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## NOGA$4ME

SoFlaModel3 said:


> Of course early days I may have lead right foot syndrome and it could be worse


A lead foot on its own will not hurt your efficiency (much). You'll spend more on tires of course...

Jack rabbit starts off the line hurting efficiency is an internal combustion engine issue and doesn't apply the same way for electric motors, thanks to the torque curve of a motor. There are minimal losses due to increased IR drop when you floor it, but nothing as near significant as the inefficiency of a gas vehicle.

If the light turns green at an on-ramp to a highway and you accelerate to 70mph, you use pretty much exactly the same amount of energy to reach that speed regardless of whether you do it in 5.5 seconds or 55 seconds.

That said, obviously any time you accelerate you are expending energy. So if you are in stop and go traffic and having to accelerate, followed by using your brakes, followed by accelerating, etc. then all those accelerations will add up (and even though you can regen, you never get as much back out as you put in). If you are accelerating off the line only to have to immediately slow down at the next light or when you catch up to the cars ahead, then yes, you are driving inefficiently. It would be more efficient to accelerate at a rate just fast enough that you can coast and avoid the repeated accelerations.

(Having said that, unless I can directly see otherwise, my mindset is that I may be just as likely to MAKE the next light as I might be to miss it, so I may as well gun it!)


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## gregincal

I don’t blame you for still being slightly confused by people’s overly complicated way of inverting the numbers twice. Try this: 254 wh/mile is .254 kWh/mile. That’s basically 1/4 kWh/mile. If your electricity is 12 cents per kWh it will cost you about 3 cents per mile.


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## Dogwhistle

Yeah, inverting wh/mile to Miles/kWh makes the math much easier. For simplicity sake, I just plan on 4 miles/kWh, which is about what I get in my i3.


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## NOGA$4ME

Dogwhistle said:


> Yeah, inverting wh/mile to Miles/kWh makes the math much easier. For simplicity sake, I just plan on 4 miles/kWh, which is about what I get in my i3.


Like you, I'm used to dealing with miles/kWh because that's how my car reports it. But for figuring out cost, Wh/mile (or more directly, kWh/mile) is actually much more convenient. Just multiply the number by the number of miles you drive and voila, you have your cost.


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## BigBri

These stats might be interesting/useful. I have a device plugged into the ODB port on the car that collects a ton of data from it. I'm part of a pilot program that tracks EV owners routes/charging habits so the data can be provided to utilities and (presumably sold) to third parties that are trying to install charging networks.

I've had my Leaf since July but it spent 2-3 weeks in the garage as the charging port on it was damaged fresh from the dealership. So I've more had it from around mid August. My EVSE at home tracks my overall savings of gas VS my electricity cost. I update the gas prices every few weeks and calculate my average electricity cost when my bill comes in. My average seems to be around 15.2C/KW.

My EVSE has calculated about $697 in savings from August til now in terms of gas savings. I can say I have noticed a BIG difference. My electricity bill is generally around $130 and that includes the car. Last month it was $100 and that was including 1500km of driving.


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## ahagge

@BigBri - can I ask what EVSE you have and what pilot program you're enrolled in? The information you are provided seems very useful...


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## danzgator

@Mike Land FWIW I drive about 35 miles a day to and from work, plus whatever weekend driving I do. I charge about 30-40% of that at work for free. I think our rates are about the same in Florida, as in AZ, and I am hard pressed to find a noticeable difference in my electric bill pre-Tesla. This isn't a very scientific answer, but I can't imagine that I'm paying more than $15-20 more per month to charge my car.


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## BigBri

ahagge said:


> @BigBri - can I ask what EVSE you have and what pilot program you're enrolled in? The information you are provided seems very useful...


This is the EVSE: https://emotorwerks.com/store/residential/juicebox-pro-40-smart-40-amp-evse-with-24-foot-cable

The program is called Charge the North so it's a Canadian thing. Might be something similar in your area or even just an ODB tool you can buy. I think Leaf Spy enables you to get similar stats out of the Leaf but I've got no experience with it as it's like $25 for the app.


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## ahagge

@BigBri - Thanks! The JuiceBox Pro 40 is one of the EVSEs on my short list to replace my aging Blink unit that came with my LEAF in 2011. Nice to see one of its displays. And I've had LEAF Spy Pro for the past 3 years or so - very useful info - $15.00 in the Google Play Store.

And to the topic - yes, I find it much easier to calculate with mi/kWH than Wh/mi. My LEAF averages around 4-4.3, so I just work with 4 mi/kWH. Looks like Model 3 will be quite similar, and impressively better than the Model S.


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## 3V Pilot

NOGA$4ME said:


> A lead foot on its own will not hurt your efficiency (much). You'll spend more on tires of course...
> 
> Jack rabbit starts off the line hurting efficiency is an internal combustion engine issue and doesn't apply the same way for electric motors, thanks to the torque curve of a motor. There are minimal losses due to increased IR drop when you floor it, but nothing as near significant as the inefficiency of a gas vehicle.
> 
> If the light turns green at an on-ramp to a highway and you accelerate to 70mph, you use pretty much exactly the same amount of energy to reach that speed regardless of whether you do it in 5.5 seconds or 55 seconds.
> 
> That said, obviously any time you accelerate you are expending energy. So if you are in stop and go traffic and having to accelerate, followed by using your brakes, followed by accelerating, etc. then all those accelerations will add up (and even though you can regen, you never get as much back out as you put in). If you are accelerating off the line only to have to immediately slow down at the next light or when you catch up to the cars ahead, then yes, you are driving inefficiently. It would be more efficient to accelerate at a rate just fast enough that you can coast and avoid the repeated accelerations.
> 
> (Having said that, unless I can directly see otherwise, my mindset is that I may be just as likely to MAKE the next light as I might be to miss it, so I may as well gun it!)


This is all good info and I'm starting to understand it better, thanks everyone for responding. The one thing I didn't realize but makes a lot of sense is the efficiency of an electric motor to accelerate quickly without "burning" much more energy. It will be fun to use the power of the car with less of a concern for it costing much more at the pump, or in this case the plug. Plus without the roar of an engine there won't be any cops turning their heads to look. I'd say it's the perfect car for some fun, spirited driving.


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## danzgator

Mike Land said:


> This is all good info and I'm starting to understand it better, thanks everyone for responding. The one thing I didn't realize but makes a lot of sense is the efficiency of an electric motor to accelerate quickly without "burning" much more energy. It will be fun to use the power of the car with less of a concern for it costing much more at the pump, or in this case the plug. Plus without the roar of an engine there won't be any cops turning their heads to look. I'd say it's the perfect car for some fun, spirited driving.


EXCEPT for the added cost of tires that you go through very quickly with spirited driving and a heavy car.


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## 3V Pilot

Yes but tires are made for burning!


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## BigBri

ahagge said:


> @BigBri - Thanks! The JuiceBox Pro 40 is one of the EVSEs on my short list to replace my aging Blink unit that came with my LEAF in 2011. Nice to see one of its displays. And I've had LEAF Spy Pro for the past 3 years or so - very useful info - $15.00 in the Google Play Store.
> 
> And to the topic - yes, I find it much easier to calculate with mi/kWH than Wh/mi. My LEAF averages around 4-4.3, so I just work with 4 mi/kWH. Looks like Model 3 will be quite similar, and impressively better than the Model S.


The interface is from my ODB device actually. I do use info from the ODB to get the correct calculations in the Juicebox. This is the interface/mobile app for the Juicebox.

The ODB device is a Fleetcarma C2 which I don't think you can just buy at this point, they're thing is mostly fleet management but the program I'm part of hands em out.


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## Topher

If I can be permitted a short lesson:

The key is UNITS.
You have: Wh/Mile and Cents/kWh.
You know Wh/kWh.
You want Cents/Mile.

So you want to make an equation which starts with the units of what you have and know, and ends with the units of what you want.

Thus 254 Wh/Mile (you want to get rid of the Wh, but the Miles is in the right place).
Multiple by kWh/Wh (which is just Wh/kWh inverted, so 1/1000 kWh/Wh), canceling the Wh, to get kWh/Mile.
Multiple by Cents/kWh (canceling out the kWh, to get Cents/Mile) in this case 12 Cents/kWh.
Equals 254 * 1/1000 * 12 = 3.048 Cents/Mile.

Thank you kindly.


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## MichelT3

Mike Land said:


> Yes but tires are made for burning!


Which adds to the micro dust which is a growing burden on our cities. Anti-EV fossils are even using the extra tirewear as an argument to oppose EV's.


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## 3V Pilot

MichelT3 said:


> Which adds to the micro dust which is a growing burden on our cities. Anti-EV fossils are even using the extra tirewear as an argument to oppose EV's.


Micro dust will be the least of their worries as I'm billowing white tire smoke and throwing off huge chunks of molten rubber as my tires melt back into the ground from which the came!! (and before you say it, YES, I know you can't do that unless they let you turn off the traction control.....I was just attempting to make a funny!)

Seriously, if some environmentalist, EV hater or anybody else wants to worry about some tiny amount of "Micro Dust" that one car "might" produce more of versus another I'd say they need to go get a life! Everybody is SO obsessed with not offending anybody or anything or destroying the planet every time a cow farts that it's gotten beyond ridiculous. I know I'm in the minority here but I'm not buying this car to save the planet or even to "do my part". I could really care less. If there were a black smoke billowing diesel 4x4 that cost less per mile to drive and had less moving parts, needed less maintenance and drove like this car does I'd buy it instead. I know it's blasphemy to say that here on this forum but it's truly the way I feel. I'm buying this car because I think it's a great achievement of "out of the box" thinking, brilliant engineering, and I absolutely believe it will outlast ANY other car currently produced with much less cost in the long run. Plus it's incredible to drive and I'm a total tech geek at heart. The fact that I can drive it quickly without it costing much more or being noticed by the boys in blue is just icing on the cake!


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## garsh

Mike Land said:


> I know I'm in the minority here but I'm not buying this car to save the planet or even to "do my part"


https://teslaownersonline.com/threads/model-3-roof-rack.4560/page-2#post-50787


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## 3V Pilot

garsh said:


> https://teslaownersonline.com/threads/model-3-roof-rack.4560/page-2#post-50787


Just when I thought I'd be banned for life because of my previous post you go and make me laugh!.....that post is hilarious....well, except for the part about driving a leaf, that part made me cry a little...


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## Brokedoc

I didn’t realize the Model 3 was THAT much more efficient than other Teslas. I was expecting an average of around 300 Wh/mi which I would round to a little over 3 mi/kWh (1000/300)

My Model X currently does about 350-400 Wh/mi but the cold winters use more energy with the heaters than the A/C in the summer where I would estimate 300-350 Wh/mi.

FWIW - the Tesla energy usage meter DOES take into account ALL energy use from HVAC, battery heater, seat warmers, steering wheel warmer, lights, etc. Often I will enter my parked car after preconditioning and the meter has a spike in power consumption to over 500 or more Wh/mi before I even move the car. I am not sure if it shows the same spike when preconditioning on shore power. I will have to look tomorrow am.

I definitely see a spike in energy use with jackrabbit starts but I feel the BIGGEST spike in energy use is fast highway speeds. This may be less in the Model 3s better aerodynamics but driving faster than 70-75mph in the winter seems to reward me with no better than 400-450 Wh/mi. That equals just over 2 mi/kWh. Ugh.


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## 3V Pilot

Brokedoc said:


> I didn't realize the Model 3 was THAT much more efficient than other Teslas. I was expecting an average of around 300 Wh/mi which I would round to a little over 3 mi/kWh (1000/300)
> 
> My Model X currently does about 350-400 Wh/mi but the cold winters use more energy with the heaters than the A/C in the summer where I would estimate 300-350 Wh/mi.
> 
> FWIW - the Tesla energy usage meter DOES take into account ALL energy use from HVAC, battery heater, seat warmers, steering wheel warmer, lights, etc. Often I will enter my parked car after preconditioning and the meter has a spike in power consumption to over 500 or more Wh/mi before I even move the car. I am not sure if it shows the same spike when preconditioning on shore power. I will have to look tomorrow am.
> 
> I definitely see a spike in energy use with jackrabbit starts but I feel the BIGGEST spike in energy use is fast highway speeds. This may be less in the Model 3s better aerodynamics but driving faster than 70-75mph in the winter seems to reward me with no better than 400-450 Wh/mi. That equals just over 2 mi/kWh. Ugh.


Thanks for the info, that's actually very informative. I'm glad the power meter takes everything into account, seems like a more honest way of doing it. They could of just as easily left that out of the calculations in order to make it seem like a more efficient car and that is what I would expect from just about every other auto company out there. I'm glad Tesla is unlike any other!


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## Johnm6875

Mike Land said:


> Micro dust will be the least of their worries as I'm billowing white tire smoke and throwing off huge chunks of molten rubber as my tires melt back into the ground from which the came!! (and before you say it, YES, I know you can't do that unless they let you turn off the traction control.....I was just attempting to make a funny!)
> 
> Seriously, if some environmentalist, EV hater or anybody else wants to worry about some tiny amount of "Micro Dust" that one car "might" produce more of versus another I'd say they need to go get a life! Everybody is SO obsessed with not offending anybody or anything or destroying the planet every time a cow farts that it's gotten beyond ridiculous. I know I'm in the minority here but I'm not buying this car to save the planet or even to "do my part". I could really care less. If there were a black smoke billowing diesel 4x4 that cost less per mile to drive and had less moving parts, needed less maintenance and drove like this car does I'd buy it instead. I know it's blasphemy to say that here on this forum but it's truly the way I feel. I'm buying this car because I think it's a great achievement of "out of the box" thinking, brilliant engineering, and I absolutely believe it will outlast ANY other car currently produced with much less cost in the long run. Plus it's incredible to drive and I'm a total tech geek at heart. The fact that I can drive it quickly without it costing much more or being noticed by the boys in blue is just icing on the cake!


Elon has you figured out and has done a marvelous job of giving you what you want to achieve what he wants. No need to push theoretical science and legislation, just provide a desirable product with desirable outcomes all around.


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## KarenRei

Brokedoc said:


> I didn't realize the Model 3 was THAT much more efficient than other Teslas. I was expecting an average of around 300 Wh/mi which I would round to a little over 3 mi/kWh (1000/300)


The efficiency is what brought me around (in the back of my head, for years I've had this stubborn, unrealistic holdout demanding I wait for something with Aptera-level efficiency if I'm to consider a new car  ). It's from several things.

1) It's much lighter than an S, let alone your X (low rolling resistance)
2) Slightly lower Cd
3) Lower cross sectional area
4) PM motor = significantly more efficient than induction on average


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## MichelT3

MichelT3 said:


> Which adds to the micro dust which is a growing burden on our cities. Anti-EV fossils are even using the extra tirewear as an argument to oppose EV's.


As an addition to myself, just stating a few facts:

In Europe traffic-emission-laws are made around three aspects, CO2, NOx and micro-dust emissions.
The latter have a local effect on building permissions.
In cities where micro-dust emissions are too high, building is restricted or even banned, because the lifespan of people is directly influenced by the exposure to micro-dust.
Traffic produces micro-dust in two forms; soot out of the exhaust and rubber particles from tire wear.
People who oppose EV's are using the extra weight and extra wide tires of EV's as an argument why EV's are 'no solution'. Totally passing the main source of micro-dust; the exhaust.
A totally ridiculous and dangerous standpoint in my view. To prevent global warming we - also - need to switch over to EV's as soon as possible, which is why Tesla should be a huge success. That a Tesla is a better car, is a means, not a goal.

EDIT: For micro-dust read Particle Matter (especially PM 2.5)


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## Guest

Just adding that "micro-dust" is usually called *particulate matter*, or PM, sometimes with a number following,
like PM10, PM2.5, specifies particle size in microns (micrometer, or 1/1000 of a millimeter).








You breath it in, and you don't breath it out.
You can find some hints that it is right next to you. Ask yourself, why wouldn't you eat this snow:


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## Matthias Fritz

to add more OT. some people argue that the electric motor in an EV is polluting micro particles too because of the electric arc. or was it even CO2? who knows. tin foil stuff i guess.


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## MichelT3

arnis said:


> Just adding that "micro-dust" is usually called *particulate matter*, or PM, sometimes with a number following,
> like PM10, PM2.5, specifies particle size in microns (micrometer, or 1/1000 of a millimeter).
> 
> You breath it in, and you don't breath it out.
> You can find some hints that it is right next to you. Ask yourself, why wouldn't you eat this snow:


Exactly. Being a non-native-English speaker, the right terms are sometimes difficult.

Old style (atmospheric and turbo) diesels emit mainly PM10 (soot). 
But new high-pressure diesels AND high-pressure gas engines emit a lot of PM 2.5 (or even smaller) which is supposed to be even more dangerous.


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## KarenRei

Matthias Fritz said:


> to add more OT. some people argue that the electric motor in an EV is polluting micro particles too because of the electric arc. or was it even CO2? who knows. tin foil stuff i guess.


LOL. Do they actually think modern EVs are based on motors with commutators? I suppose they're also driven by lead-acid or maybe nickel-cadmium batteries as well? 

There is, of course, no gap to "spark" in a brushless motor. Current to the coils is controlled by IGBTs in the inverter/controller. By contrast, there's plenty of sparking in an ICE, which uses literal _spark plugs_.


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