Re: Aptera diesel-electric hybrid car gets 300 miles per gallon and will cost $29k.

BobG wrote:

In a flat country like Holland maybe ?
Graham
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wrote:

I did a google for "road horsepower" and the first link was for a Toyota MR2.
http://www.mr2.com/MR2TechData.html
A test by Car & Driver put it at 14.0 hp @ 50 mph. That would be 14*. 746.444 KW, which is what would be needed to cover 50 miles. 10.444/50 = .20888 KW hr/mi. An efficiency of 85% would not be unrealistic and would give .20888/.85 = .246 KWhr/mi. This thing looks like it probably has a lower CD than an MR2. BTW that 14.0 hp was broken down into
Friction and tire losses @ 50 mph ..... 5.5 hp Aerodynamic drag @ 50 mph ............. 8.5 hp
Bruce
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On Sun, 21 Oct 2007 17:09:56 -0700, " snipped-for-privacy@my-deja.com"

I think you missed something here. According to your figures, it will take just over 200 watts to move the car at 50 mph for one mile. That's not the figure given of 14 hp, that's more like 1/4 hp expended to move one mile. You have to expend that power at a constant rate of 14 hp or 10.444 kW. Look at it another way.
W=ExI
Where    W=watt         E=voltage         I=current (in amps)
To make the math easer, assume you have a 100 volt battery. Then solve for current using:
I=W/E    I444watts / 100volts I4.44amps
We have a constant current draw of 104.44 amps required to propel the car at 50 mph. That is the reason why it is really hard to get an electric car to have a reasonable range (200 miles) at a reasonable speed (50 mph). You would be looking at a total power expenditure of over 41.7 kW to drive for 200 miles at 50 mph. That figure assumes no head wind and level ground. Add in real life conditions and you might be looking at power expenditures of around 45 to 50 kW. Also, you'd flat get run over driving around here on the highway at 50 mph. You'd better be traveling at least 60 mph which would boost your totals even more.
Even if you had a battery that could deliver that much power, you still have the problem of getting all that power back into the battery. In order to replace 41.7 kW using your 120 vac outlet, you need to draw over 41 amps for 8 hours. That is assuming 100% recharge efficiency.
You can draw your own conclusions regarding the practicality electric cars.
Jack
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Retired VIP wrote:

...
No, it takes 10.444 kW to move the car at 50 mph. It takes just over 200 watt-hours to move the car one mile at 50 mph.

Why not 300V? 600V? 1000V? Wouldn't higher voltage be easier for the electronics than lower voltage?

It's not the amps, it's the wattage. It's all 10kW no matter how you slice it. If this was a 1000V system then it would only be 10.4 amps. 10 Amps doesn't sound like a problem.

Those new lithium batteries seem to be able to give 200+ mile range to electric cars without any problems (except being expensive). I would imagine you would recharge using a 220V appliance outlet like they use for electric dryers, electric ovens and air conditioners. Besides, who drives 200+ miles a day? If you drive only 30 or 40 miles then the battery won't be completely flat and it won't take as much to recharge.
Anthony
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On Sun, 21 Oct 2007 22:16:05 -0700, Anthony Matonak

How can it take 10.444 kW to move a car at 50 mph but only 200 w/hr to move a car at 50 mph? Remember that a w/hr is a unit of power for a period of time. A watt is a unit of power without reference to time.

You could use any battery voltage you wish. I chose 100 volts to make the math easier to follow. The battery voltage would have no effect on the power requirement.

It IS the amps and the voltage and the current and the wattage. They are all related. Power in watts is voltage time current. Yes, you could use a 1000 volt battery and it would only require a current draw of 10.4 amps. The power would be the same.

You still have to put the power used back into the battery regardless of what voltage you use to power the charger or what type of battery you use.
What about the poor guy who has to travel 1000 miles in his electric car. Does he drive 200 miles then stop for 8 hours while the battery is recharged?
Jack
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Retired VIP wrote:

Would you prefer if we said that it takes 10.444 kWh to move a car 50 miles in one hour? How about that it takes 1/50th of that to move the car just 1/50th of that distance in 1/50th of that time?
I'll let you do the math. Hint. 1/50th of 50 miles is 1 mile. (I'll let someone else describe w/hr and Whr differences.) :)

The wiring in most houses is limited in amperage. Say your car can only draw 30A from the outlet. If the outlet is 220V then it can get twice the power than it could if it was 120V. A car that would need 8 hours to recharge on 120V would only need 4 hours on 220V.
Your complaint seems to be that it would take too long to recharge a car at 120V. I suggest that it wouldn't take too long at 220V.

What about the poor guy who has to travel 4000 miles? What does he do for speeding tickets and sleep?
Around these parts, it would take over 18 hours to drive 1000 miles and anyone who has to drive more than a 1000 miles a day has got bigger problems than where to plug in his car.
Assuming your car gets some 5 miles/kWh and you get to recharge using a typical 220V 30A outlet. It would only require 6 hours of recharging for every 200 miles of driving (more or less). This sounds reasonable to me.
Some folks have been suggesting the use of 'quick charge' outlets that provide higher voltage, current or both. These could recharge the car while eating lunch (or dinner).
Anthony
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wrote:

That number should be 500miles per day...at least if the driver wants to stay legel and safe.Roughly what a solo truck driver does in a day. But then that also begs to explain as well ,if electric power is cheaper to operate.And can do the the range across country without delay,with the potential of savings for the driver.Why are we starting out with cars instead of battery powered trains and 18wheelers?Hell the trains in most of the country already have thier 600v computer controled traction motor already installed.Now how many of them everlasting batteries do we for a 6000hp locomotive.They sometime run more than one locomotive in a consist.....but I guess we can multiple that one locomotive number on whatever the consist requires. At the same ,time I remember some trains were striaght electric.You think ,there might be a reason for most to run diesel on a generator,instead of electric off an overhead or batteries.

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To maintain a speed of 50 mph it takes 10.444 KW (note KW not KWhr). If you travel at 50 mph for one hour you will have gone 50 miles and you will have drawn 10.444 KW for one hour, meaning you used 10.444 KWhr. To only travel one mile would only take 1/50=.02 hrs. If you draw 10.444 KW for .02 hr then you used 10.444*.02=.20888 KWhr or 208.88 watt-hours.

Your complaint seemed to be about the high current draw. Using a higher voltage reduces the current. And actually it does have an effect on the power requirement. Part of the power requirement is providing for power losses due to resistance heating in the batteries, wiring and motors. Those heat losses are proportional to the square of the current. Go from 100V to 200V and the resistance losses are cut to 1/4 of what they were. That also means you can work the motor harder without over heating it.

Take his other car? Take the bus? Rent another car? The electric may not be able to do all things, but if it can get the equivelent of 160 mpg or more for the vast majority of your traveling then maybe you can afford to make other arangements for those trips that it isn't suitable for.
Another possibility would be to have an engine just big enough to provide the power needed for a steady state cruise at the highest speed you need to go. When going slower the batteries could be charged on the fly so there would be more power availible for acceleration or climbing hills. Something like this
http://tinyurl.com/22d3n6
should let you cruise at 70 mph while using .9 gal/hr. That works out to 77 mpg.
Bruce
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Read it again. That is 200 watt hours. Yes, a 1/4 hp motor should be able to move the car 1 mile in an hour. And a 1 hp motor could move it 4 miles in an hour. And a 2 hp motor could move it 8 miles in an hour. And a 14 hp motor could move it 50 miles in an hour. A watt is energy per unit of time, same as hp. A watt hour is a unit of energy, as would be a hp hour. Spread that energy out over a long period of time and the power is low, but the amount of work that can be done is the same.

The claim made was 120 miles, not 200, and the car should use less than the 14 hp to go 50 mph. That was the power required to keep a Toyota MR2 going 50 mph. Even at 14 hp it would only take 10.444*2.4% KW hrs to go 120 miles. It would not be unrealistic to expect this smaller car with better arodynamics to do 50 mph using 10 hp, which would mean about 18 KW hrs to do 120 miles.

120 volts * 20 amps is 2400 watts. 18 KW hrs / 2400 watts = 7.5 hrs. They did say to plug it in at night, and that it would be recharged in a few hours. They were probably stretching things a bit, but not all that much.
Bruce

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18KWhrs at $.12 would cost me about $2.16 in Florida... Thats about what .75 gal costs this week... 120 miles on .75 gal would be 160 mpg equivalent.... sounds hi to me... 100mpg equiv I might believe....
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Try getting off peak power. Plug it in and let it charge while you sleep for about half the cost of daytime power. What makes you think the $/mi should be the same as for gasoline?
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On Sun, 21 Oct 2007 22:29:47 -0700, " snipped-for-privacy@my-deja.com"

So 4 hp would move the car 16 miles in an hour (16 mph). A 8 hp motor would move the car 32 miles. A 16 hp motor would move the car 64 miles. And it would take a 32 hp motor to move the car 128 mph. Holly smokes, my car should be able to travel at well over 400 mph using its 120 hp motor. Do you see something wrong with this progression?
A watt is a unit of power without regard to time. A wHr is a unit of work. 10 watts isn't the same as 100 watts but 10 watts applied to a device for 10 hours will do the same amount of work as 100 watts applied for 1 hour. The same is true of horsepower, it's a measurement of power not work. A hpHr is a measurement of work.
So, if it takes 14 hp to move a car at 50 mph without regard to time. It will take 14 hp to move that car at 50 mph for one minute or one hour. The only difference is the amount of work done, not the amount of power needed.
So, his figure of 200 watts to move a car at 50 mph is wrong.
Jack
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Sure, I made it linear rather than exponential to keep things simple. The further you get from the 50 mph starting point the further off you will be. The point was that 1/4 hp would move the car 1 mile in an hour. That's traveling 1mph for an hour.

It was 200 watt-hours to move the car one mile in 1/50 hrs. If you want to go 50 miles in an hour it will take 50 times that.

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On Mon, 22 Oct 2007 22:14:58 -0700, " snipped-for-privacy@my-deja.com"

I give up. You folks seem to be unable to understand that there is a difference between power and work.
Jack
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Sorry but you're the one that seems to have things mixed up.
If you apply a force over a distance you have work. Say you push with a force of 11 pounds for a distance of 50 feet , you have done 550 foot pounds of work. Time doesn't enter into it. It is 550 foot pounds of work whether you do it in ten seconds or ten minutes.
Power is how much work is done in a given time. 550 foot pounds per second is one horsepower. So if we pushed the object above the 50 feet in one second it would have been 1 hp. But it took 10 times that long so we were producing .1 hp.
Watts are power. 1 hp = 746 watts.
If we specify a power output for a specific period of time the result is an answer in work. Look at the units. Power is foot pounds divided time, and you are multiplying by time. The times cancel out leaving you with foot pounds.
The same thing applies to watts. A watt is current times voltage. The current is flow per unit of time. So when you specify a time period for those watts you multiply by that time and get the work done during that time.
In the original example we knew it took 10,000 watts to maintain a speed of 50 mph. We know that at that speed it takes .02 hours to cover 1 mile. Multiply the power (10,000 watts) by the time (.02 hours) and you get an answer in units of work (watt hours). If we had multiplied the power in horsepower by the time we would have gotten an answer in horsepower hours which can be converted into foot pounds.
The 200 watt hours seems like a small number compared to 10 KW, but it is the work done in a short period of time (.02 hours). If you do the same thing 50 times it will take 200*50,000 watt hours over a period of 1 hour. Or go at it the other way around. Divide 200 watt hours by .02 hours. The time units cancel out leaving 10,000 watts.
Starting to make sense?
Bruce
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