# Help Guesstimating Power Consumption



## highamperage (Mar 15, 2011)

Hey! I need some help guesstimating my watts/hour/mile for an electric truck on the drawing board. 

I am looking at the following setup:


2008 Silverado 1500 at around 4600lbs
Kostov 13" Motor @ 250VDC
WarpDrive 360VDC/1400amp Controller
34kw/340volt Lithium Pack
According to my math, it looks like it will use 480 per mile @ 65mph. Based on 28ft frontal area, .45 drag coefficient. However. I was looking around EVAlbum and saw a few other vehicles, one being a large full size truck using around 1040wattshour/mile, and an F150 claiming to use about 350. 

I know the larger truck on EVAlbum had lead acid batteries weighing it down and a high Perkuet number to deal with. Also most people seem to measure amount of power per mile from the charger, for this I am more concerned with calculating range, not my electric bill. 

What do you guys think? (Let's assume I drive rationally, also - no racing haha)


----------



## Yabert (Feb 7, 2010)

Hi

I put your numbers in a calculator (65 mph, 5000 lbs, 28 ft front, 0.45 drag) and the result is 630 Wh/miles.
The result change drastically to over 1100 Wh/miles if I set the Hill Incline value to 2 degree.

But your front area seem really small for a truck. The front area of my Smart is 22 square ft.


----------



## bluefxstc (Dec 29, 2007)

I heard that 8000W is approximately equal to a gal of gas. If your truck was rated for 20 miles per gal then about 8000W should get you about 20 miles. It worked out well for my conversion.


----------



## Bowser330 (Jun 15, 2008)

Checkout Ecomodder.com for ways to reduce your overall drag coefficient...
Grill Blocks, under body tray/cover, smaller mirrors, lowering, etc...

I'm very interested to see how it all comes together, keep us posted!


----------



## efan (Aug 27, 2009)

hey guys, 
I have a question that is related to power calculation: How do I calculate how much power (hp) I need to drive 55mph on an incline of say 30%?
Lets say that the finished ev weights 2500lb and I needed to drive on a grade ~30% for about 0.6mi at speeds around 55mph, can I do that with DC conversion? and what kind of voltage would I need the system to run at?

thanks for any help!


----------



## highamperage (Mar 15, 2011)

bluefxstc said:


> I heard that 8000W is approximately equal to a gal of gas. If your truck was rated for 20 miles per gal then about 8000W should get you about 20 miles. It worked out well for my conversion.


That would be a dream. Can anyone else comment on this? That is on par with what I've seen on some people's EVAlbum posts, but certainly not others...

Also, Yabert... can you send that calcuator to me?


----------



## Yabert (Feb 7, 2010)

> Also, Yabert... can you send that calcuator to me?


Yes.... if any people can said to me how I can put a Excel sheet on the forum!..


----------



## rankhornjp (Nov 26, 2007)

bluefxstc said:


> I heard that 8000W is approximately equal to a gal of gas. If your truck was rated for 20 miles per gal then about 8000W should get you about 20 miles. It worked out well for my conversion.


1 gal of gas contains 125000 BTUs. So converting BTUs to WATTS, you get + or - 36000 watts, depending on which online calculator you use.


----------



## tomofreno (Mar 3, 2009)

> I heard that 8000W is approximately equal to a gal of gas.


 The Department of Energy uses an energy of 33.7 kWh/gallon. That's 8000W for about 4.2 hours.


----------



## RE Farmer (Aug 8, 2009)

tomofreno said:


> The Department of Energy uses an energy of 33.7 kWh/gallon. That's 8000W for about 4.2 hours.


Yes, but ICE are only 15-20% efficient while EVs are ~80% efficient to the wheels. So only 5-7 kWh/gal move the car; the rest warms the atmosphere.


----------



## bluefxstc (Dec 29, 2007)

My car is using 400 w/mile out of the wall. EPA fuel consumption rated it at 19-21 mpg. Figuring an average of 20 mpg for my car with an ice. That work out to 20*400 or, 8000W per gal of gas, approximately. I don’t know where I heard it. I am not smart enough to figure the math out but it worked out pretty close for my car. It will not be an exact number for every situation but it seems to be pretty close.
Bluefxstc


----------



## Franky.EV (Feb 27, 2010)

Try this :

http://www.diyelectriccar.com/forums/showthread.php/yes-another-ev-calculator-45278p7.html

Maybe it can help you.


----------



## tomofreno (Mar 3, 2009)

> My car is using 400 w/mile out of the wall. EPA fuel consumption rated it at 19-21 mpg. Figuring an average of 20 mpg for my car with an ice. That work out to 20*400 or, 8000W per gal of gas, approximately. I don’t know where I heard it. I am not smart enough to figure the math out but it worked out pretty close for my car. It will not be an exact number for every situation but it seems to be pretty close.


 You mean 400 Wh, Watt-hours, not Watt. Watt-hours is a unit of energy, Watt is a unit of power, which is energy per unit time. It takes energy per unit time, power, to keep a car moving at constant speed, so it consumes energy per time and energy per mile.

Most of the energy stored in the gasoline is dissipated as heat in an internal combustion engine, with only roughly 20% used to move the vehicle. You are neglecting that 80% in your calculation. So 8kWh is only about 20% of the energy used from the gasoline, and 8kWh/0.2 = 40kWh, 32kWh dissipated as heat and 8kWh used to move the vehicle, which overestimates the energy in a gallon of gasoline a bit. If we assume all ice's are 20% efficient, your calculation certainly gives some guidance, but I think efficiency actually varies significantly, especially from older to newer vehicles. My car was rated at 32 mpg by EPA, and uses about 216 Wh/mile from the wall. The product gives 6912.

Also, if you have an electric heater in your ev, using it will increase your energy/mile, but using the heater in an ice-powered car will not effect your mpg as the heat would be dissipated by the engine whether you make use of it or not.

I think there is less variation using the EPA number for Wh per gallon of gas, but that is just an average since it varies a bit with grade of gasoline.


----------

