From: Barnett
Williams

Date: Sat, 11 Mar 2000

I have made an Excel spread sheet which calculates the energy
used by a vehicle while traveling through city traffic. In it I
can add or remove stop signs and rolling hills. The vehicle
weight, rolling resistance and CdA are all adjustable. It is
useful for figuring out the impact of changing certain parameters
like aerodynamics, rolling resistance, weight, and regenerative
braking. When I insert parameters for a fully faired, electric
trike (CdA=.6 sq. ft, Crr=0.05, mass =86 lbs, rider mass = 210
lbs, motor efficiency = .8, gearing efficiency =.9 and a charging
efficiency =.95) and use 2 stops per kilometer, flat land, I get
a 45 % increase in range when I use regen braking. The top speed
was limited to 50 kph and a 750 watt motor was used with a 100
watt*hour battery pack. The range with the regen was 11.36 kms
and without it the range was 7.82 kms. This seems like a pretty
useful feature to have. I used a smaller battery back than one
might want, just to limit the amount of calculations necessary.
The 86 lb vehicle would likely have a 500 watt*hour pack. I doubt
that full 45% increase could be realized under similar real life
condidtions, but it gives an indication of the upper limit.

The trike is of course a very high performance imaginary vehicle.
It is possible to build such a vehicle with conventional
materials and design constraints. Many racing desgins could be
modifed to satisfy the cirteria given above. The poorer the
performance of the vehicle, the less advantage one will get from
a regen system.

Using 76 lb bare trike with a CdA of 3 sq. ft and Crr of 0.01,
the range without regen is 4.95 km and with it the range is 6.055
km. Here the increase in range is only 22% and the range itself
is almost cut in half.

You can find the calculator at

http://www.eng.uwaterloo.ca/student/bkwillia/index.html

Drag as many lines down as you require.

Barnett Williams

Thursday, 29 January 2009