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Old 02-11-2012, 10:27 AM   #11 (permalink)
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Just to add another perspective, the units of watt*hr/mi are newtons, which is force. You are measuring how much force is acting against the car at a given speed. Higher speed means more force pushing against the car.

(watt) * hr / (mi) =
(newton*meter/sec) * 3600sec / (1609.344meter) =

2.237 newton

------------------------------------------------------------------------
One newton is 0.225 pounds of force, so a 400watt*hr/mi car would need a guy pushing it with
2.2237*0.225*400 = 200 pounds

of force to keep it moving at the rate it's going.

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Old 02-12-2012, 06:09 PM   #12 (permalink)
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Quote:
Originally Posted by MPaulHolmes View Post
Just to add another perspective, the units of watt*hr/mi are newtons, which is force. You are measuring how much force is acting against the car at a given speed. Higher speed means more force pushing against the car.

(watt) * hr / (mi) =
(newton*meter/sec) * 3600sec / (1609.344meter) =

2.237 newton

------------------------------------------------------------------------
One newton is 0.225 pounds of force, so a 400watt*hr/mi car would need a guy pushing it with
2.2237*0.225*400 = 200 pounds

of force to keep it moving at the rate it's going.
240V and 90A is 21450 Watts. at 746W per hp it's taking 28.8 hp to push that car along. how can 28.8 hp equal 200 pounds of force required to push it along? something not right

is there a page for how much hp is required to push a car along at highway speeds? would like to see some figures
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Old 02-12-2012, 07:35 PM   #13 (permalink)
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Voltage*current is Power. Watts is power, and HP is power. It's not force.

BUT!

If you divide power by speed you get watt*hr/mi (which is FORCE). So, if you know the speed you are which you are traveling, you can find the watt*hr/mi...

In the example you gave:

240v*90amp = 21450 watt of POWER. That is the same as 28.8 horsepower of POWER.

Let's say you were measuring that 240 volts and 90 amps at 50 miles per hour.

That would be 240*90/50 watt*hr/mi = 429 watt*hr/mi.

Let's say you measured 240v and 90 amps at 100 miles per hour.

That would be 240*90/100 watt*hr/mi = 214.15 watt*hr/mi.

Let's say you have a big fat slug of a car. 240v and 90 amps at only 10 miles per hour.

That would be 240*90/10 watt*hr/mi = 2160 watt*hr/mi.

Ecomodders would come from all around and hunt you down and kill you! hahaha
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Old 02-12-2012, 07:58 PM   #14 (permalink)
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my car is a big fat turd. 10.5 mpg. if calculated to power it would be lots. there is no way it is only 30 hp to push it to 50mph
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Old 02-12-2012, 08:04 PM   #15 (permalink)
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slightly off topic, how come a 2.25L turbo diesel gets 30mpg, a 4.0Lv8 gets 15mpg and an electric motor needs 30hp to do the same work?
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Old 02-12-2012, 08:24 PM   #16 (permalink)
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Quote:
Originally Posted by bandit86 View Post
my car is a big fat turd. 10.5 mpg. if calculated to power it would be lots
ROFL!!!!

Hey! we could convert mpg to watt*hr/mi I bet! gallons per miles is amount of energy per mile which is watt*hr/mi!
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Old 02-12-2012, 08:50 PM   #17 (permalink)
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And what would that big number be?
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Old 02-12-2012, 09:12 PM   #18 (permalink)
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Let's do some figgerin'!

130,000,000 Joules of energy in a gallon of gas.

Let's assume that the engine is 15% efficient?

So, 0.15*130,000,000 Joules to go 10.5 miles.

19,500,000 joules to go 10.5 miles.

There are 3600 joules in a watt*hr, so...

(19,500,000 joules) * (watt*hr)/(3600 joules) / (10.5 miles) =

515.9 watt*hr per mile!

The real world value would be a bit worse, because volts and amps first have to go through a controller and a motor. So I bet it's more like 650 watt*hr/mi.
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Old 02-12-2012, 10:00 PM   #19 (permalink)
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Holly crap it's close. What about diesel?
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Old 02-13-2012, 12:40 AM   #20 (permalink)
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Diesel is 155,000,000 joules per gallon instead... If you get 10.5 mpg still, then the watt*hr/mi is even worse! 155/133 * 650

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