EV miles/kwh and range - Page 3 - Kia Niro Forum
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post #21 of 52 (permalink) Old 08-30-2019, 05:48 PM
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Originally Posted by charlesH View Post
the energy required to reach a given velocity is the same under slow acceleration (low power) or fast acceleration (high power).
You guys are way off base. The faster the acceleration, the more energy is used to reach the same speed. This applies to any motive force. No "free" ride here. Once you have gained a certain speed, it is true the potential energy from your momentum is now the same.
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post #22 of 52 (permalink) Old 08-30-2019, 07:37 PM
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You guys are way off base. The faster the acceleration, the more energy is used to reach the same speed. This applies to any motive force. No "free" ride here. Once you have gained a certain speed, it is true the potential energy from your momentum is now the same.
Simply not true.

The energy (called kinetic) of a moving body is 1/2mv^2 (FYI momentum is mv. not the same as energy). It doesn't matter how quickly you accelerate the car. The energy required is the same. m and v only. There is no acceleration "a" term in the equation.

If you want to accelerate quickly then you do need more power (kw or HP). If your source of power is efficient over a wide power band then you will be just as efficient accelerating quickly as accelerating slowly.

energy = power X time. (v=a X t ). Kw is power. Kwhrs is energy. 10 kw X 20sec = 20 kw X 10sec. Yes, twice the acceleration requires twice the power but it is only applied for half the time to reach the same velocity.

A motor/battery combo is quite efficient over a wide power band unlike an ICE which needs a lot of gears to stay in its most efficient power zone. This is one reason why hev/phev/EV are more efficient than ice cars in city driving. (Regen braking is the other big reason.)

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post #23 of 52 (permalink) Old 08-30-2019, 10:33 PM
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"It doesn't matter how quickly you accelerate the car. The energy required is the same."

I would concur with that, solely from my observations of the SoC display in the car. I have two options to reach the top of the hill I live on. Both routes are the same distance, but one goes to the right, is steeper with a stop sign about half way up, then more climbing. The other way goes to the left, winding around but with a less inclined road. They both reach a stop light at the top. I can take the steeper route, which requires harder acceleration, and the SoC shows 95% at the top (leaving the garage indicating 100%). I can take the shallower route, and really baby the throttle, and I still show 95% at the stoplight. So, traveling the same distance, with two different driving patterns, but the same amount of power used either way.

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post #24 of 52 (permalink) Old 08-30-2019, 11:29 PM
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"It doesn't matter how quickly you accelerate the car. The energy required is the same."

I would concur with that, solely from my observations of the SoC display in the car. I have two options to reach the top of the hill I live on. Both routes are the same distance, but one goes to the right, is steeper with a stop sign about half way up, then more climbing. The other way goes to the left, winding around but with a less inclined road. They both reach a stop light at the top. I can take the steeper route, which requires harder acceleration, and the SoC shows 95% at the top (leaving the garage indicating 100%). I can take the shallower route, and really baby the throttle, and I still show 95% at the stoplight. So, traveling the same distance, with two different driving patterns, but the same amount of power used either way.
actually your consuming energy climbing a hill in addition to what ever energy is used to accelerate the car.

Still the principle is the same. The potential energy stored up climbing the hill is the same whether you climb via a steep road or or a gentle road.

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post #25 of 52 (permalink) Old 08-31-2019, 02:07 AM
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Ok, before we all are going to “kill each other” on how well we remembered the stuff we had to learn during physics class, let us go back to a practical example to figure out why you should use EV mode in the city and ICE on the highway. That is if you have the PHEV.

As someone rightfully stated the power an ICE can produce is not constant over the total range of RPM available to propel the car. This has been THE engineering challenge forever since ICE were used in vehicles. To optimize the solution engineers worked forever on designing transmissions and the fuel burning process. Electromotors have the ability to pretty much use the maximum power over the complete RPM range. That is why there is no need for a transmission in an EV.
Engineers have studied and experimented at length what will create overal average the best fuel consumption for a car without sacrificing too much performance. The result remains a sub-optimal energy consumption.

I can’t say my driving is typical, but I have driven 2 cars that are about the same size and shape (Niro EV and the BMW X1 2L Turbo) both having motors with roughly same power (150kW) and I drove them under the same circumstances (driving style, terrain). The long term average on my EV is 16.1 kWh/100km, my X1 consumed on average 12l/100km. I know it is metric, but for comparison this makes it a bit easier. So how much energy is in 12l of gasoline? According to this answer by a Professor 12l gasoline contains 108 kWh of energy! If I would assume that the BMW engine is highly inefficient (BMW would disagree!) at 20%, then there is almost 22kWh used per 100km to obtain the same driving. Which shows the inefficiency of the transmission, but also the lack of the ICE being able to regenerate forces to slow down the car back into the energy form it has on board (gasoline).

So long story short for the PHEV drivers: use EV mode in the city and ICE on a longer highway stretch as soon as you arrive at cruising speed.

Is the car able to detect this and automate this for you? So you don’t need any of the knowledge while driving and can listen to the music? Only when it has a location based system with data on the type of road you are on in combination with real-time traffic conditions, so it can reliable predict the driving style (e.g. GPS based navigation system you can find in the Niro). The computer making the decisions which engine to use will need this info in combinatinon with speed and the throttle position. Since a nav system in a car is still being sold as a way to find your way and still seen as a luxury for which you can charge additional money, it is not yet used for this purpose. Maybe some day it will become a competitive advantage for a car manufacturer to automate the optimal use of motors in a PHEV. I am sure the engineers have this already worked out, but the product managers and marketeers are not yet in. Time will tell!
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post #26 of 52 (permalink) Old 08-31-2019, 02:39 AM
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"It doesn't matter how quickly you accelerate the car. The energy required is the same."
[…]
So, traveling the same distance, with two different driving patterns, but the same amount of power used either way.
Your last sentence should read “energy” instead of “power”. Many folks mix these terms up, however they are not the same.
Unless these 2 routes you take exactly the same time to travel, the total of power used will be different. But that doesn’t matter, because the variable is energy and the State of Charge is a relative measurement of the total energy capacity of the battery. The power only matter for the level of acceleration and to obtain speeds.

Eg. the EV battery holds 64kWh energy, but can produce up to 170kW of electrical power. In theory if I would drive with full power the battery would be empty in 22 minutes. The car is limited at about 107 mph to prevent the motor from rotating into speeds where it could get damaged. I did this once and I recall the display showing 150kW of electric power being applied. So at max speed the battery would run out of energy in 45 miles! Hence the eco mode, which will reduce the max speed you can drive in order to force you getting better range.

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post #27 of 52 (permalink) Old 08-31-2019, 11:30 AM
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Your last sentence should read “energy” instead of “power”. Many folks mix these terms up, however they are not the same.
Yep, I knew better. Thanks for the correction.
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post #28 of 52 (permalink) Old 08-31-2019, 01:04 PM
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Your last sentence should read “energy” instead of “power”. Many folks mix these terms up, however they are not the same.
Unless these 2 routes you take exactly the same time to travel, the total of power used will be different. But that doesn’t matter, because the variable is energy and the State of Charge is a relative measurement of the total energy capacity of the battery. The power only matter for the level of acceleration and to obtain speeds.

Eg. the EV battery holds 64kWh energy, but can produce up to 170kW of electrical power. In theory if I would drive with full power the battery would be empty in 22 minutes. The car is limited at about 107 mph to prevent the motor from rotating into speeds where it could get damaged. I did this once and I recall the display showing 150kW of electric power being applied. So at max speed the battery would run out of energy in 45 miles! Hence the eco mode, which will reduce the max speed you can drive in order to force you getting better range.
Interesting. 150kW to do 107 mph? Are you sure? My phev uses ~15kW to do 80 mph. Considering wind drag effect alone (107/80)^2 = 1.8 I would have expected 15 x 1.8 = 27kW to do 107 mph

Please check again how many kW for your ev to do 40, 80, 100 mph.

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post #29 of 52 (permalink) Old 08-31-2019, 04:39 PM
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Interesting. 150kW to do 107 mph? Are you sure? My phev uses ~15kW to do 80 mph. Considering wind drag effect alone (107/80)^2 = 1.8 I would have expected 15 x 1.8 = 27kW to do 107 mph

Please check again how many kW for your ev to do 40, 80, 100 mph.
I believe the formula is bit more complicated to calculate the power as a function of speed taking drag into account. And as far I remember with drag in the equation the power is function of speed^3. I also think your relative increase calculation is the wrong way of calculating.

Now that I have a car scanner which can record all these variables from the car’s ECU, so I could definitely record a test. But keep in mind we have a speed limit of 60mph where I live... so I will need an almost empty straight highway, which is not around the corner and make sure law enforcement is not watching.
To be honest the 150kW I saw briefly (as I kept my eyes on the road) was likely while I was still accelerating. The test was more to see how the motor would keep pulling until it reaches its limit. Yes, it does keep pulling.

In the screenshots you can see the actual power used to accelerate to and maintain speed. Now keep in mind that I use adaptive cruise control in eco mode which leverages regen as good as possible and speeds up (when possible) with a modest acceleration. Speeds are in km/h. Just devide by 1.6 to get in mph. Power is in kW.
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post #30 of 52 (permalink) Old 08-31-2019, 06:47 PM
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I believe the formula is bit more complicated to calculate the power as a function of speed taking drag into account. And as far I remember with drag in the equation the power is function of speed^3. I also think your relative increase calculation is the wrong way of calculating.

Now that I have a car scanner which can record all these variables from the car’s ECU, so I could definitely record a test. But keep in mind we have a speed limit of 60mph where I live... so I will need an almost empty straight highway, which is not around the corner and make sure law enforcement is not watching.
To be honest the 150kW I saw briefly (as I kept my eyes on the road) was likely while I was still accelerating. The test was more to see how the motor would keep pulling until it reaches its limit. Yes, it does keep pulling.

In the screenshots you can see the actual power used to accelerate to and maintain speed. Now keep in mind that I use adaptive cruise control in eco mode which leverages regen as good as possible and speeds up (when possible) with a modest acceleration. Speeds are in km/h. Just devide by 1.6 to get in mph. Power is in kW.
thanks Peter, excellent data

Yes, wind resistance is proportional to v^3 but it's influence on mpg is proportional v^2. Similarly drive train friction is generally proportional to v but for MPG calculation its 1.

Yes, there must be some acceleration power included in your 150KW reading.

Your 100 kph (60mph) results show 10-20kW which is considerably higher than my experience. What kind of terrain for this run?

Good stuff.

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Last edited by charlesH; 08-31-2019 at 06:52 PM.
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