# [EVDL] Coast down test for determining watt hours per mile ? (Or motor power ?)



## EVDL List (Jul 27, 2007)

Sorry bro, I'm great on the math, but I'm going to opt
for "real world" experience.
65 mph at 144V in a 92 Honda Civic sedan will require
about 200-250amps. Sorry I can't be more accurate,
but the slightest hill makes a difference. And
without compression of cylinders working against you,
there is little coast-down. Ie, I can try to hold a 65
at 200A, and eventually I need to pump it up to 250A
for a few seconds, so likely on a perfectly
straight/flat, it's more like 225.
Similarly, 40A to 100A for a 40 mph cruise.
Best to you, 



> --- me2 <[email protected]> wrote:
> 
> >
> > I'm trying to come up with a way to gage how many
> ...


----------



## EVDL List (Jul 27, 2007)

> Bob Bath wrote:
> > Sorry bro, I'm great on the math, but I'm going to opt
> > for "real world" experience.
> > 65 mph at 144V in a 92 Honda Civic sedan will require
> ...


----------



## EVDL List (Jul 27, 2007)

I've come across a roll down test that was presented on this list some
time ago and put into a nice PDF format. It may be helpful:

http://www.2shared.com/file/3194217/d7d573b5/Roll-down_test.html

-Jon Glauser
http://www.evalbum.com/555

<quote who="me2">
>
> I'm trying to come up with a way to gage how many watt hours per mile an
> EV
> candidate will need.
>
> Has anyone done a coast down test to determine how much power or how many
> watt hours per mile a candidate will need ?
>
> Energy = 1/2 mass * velocity ^2.
>
> Take the car up to 70 MPH on a flat straight road. Put it in neutral.
> Time
> how long it will take to coast down from 70 to 60 MPH. Calculate the
> energy at 70 MPH. Calculate the energy at 60 MPH. Take the difference.
> Divide by the time, should give you the power required to roll the car at
> the mean (or the geometric mean) speed. Yes/No ?
>
> Then to figure out the motor power, add in a factor for the differential
> and
> gearbox and the motor efficiency itself. Would this work ?
>
> I'm finding it hard to gage how much power a candidate will need at 65
> MPH.
> I was using fuel consumption numbers, but they vary for the same vehicle
> depending which engine it has and what gearing it uses, so I don't think
> they would be that reliable.
>
> Comments ?
> --
> View this message in context:
> http://www.nabble.com/Coast-down-test-for-determining-watt-hours-per-mile---%28Or-motor-power--%29-tp16834875p16834875.html
> Sent from the Electric Vehicle Discussion List mailing list archive at
> Nabble.com.
>
> _______________________________________________
> For subscription options, see
> http://lists.sjsu.edu/mailman/listinfo/ev
>


_______________________________________________
For subscription options, see
http://lists.sjsu.edu/mailman/listinfo/ev


----------

