[ausev] EV Calculator Script

[Nick Viera]

Hi Charles and all,

Charles Birkhead wrote:
> I have found Uve's electric vehicle calculator
> (http://www.geocities.com/CapeCanaveral/Lab/8679/evcalc.html) to be
> useful in estimating EV performance.  It includes the peukert effect.  I
> have modified it to include internal wiring resistance and idle current
> draw.  It is relatively easy in Uve's calculator to add/modify battery
> characteristics.

I've used Uve's calculator, but it seems really inaccurate. Plus, it 
spits out a lot of numbers that are basically useless to me because they 
represent conditions that my EV could *never* achieve in real-life due 
to battery, motor, and controller limitations, which aren't accounted 
for in Uve's calculator.

> Suggested modifications to your version include:
> O  motor speed/torque/current characteristics
> O  drive gear ratio (transmission and rear axle)

What information are you looking to get out of the calculator with this 
information?  Knowing gear ratios does make it possible to calculate how 
fast you can go in each gear (i.e. the shift points). But this is the 
only calculation I can think of off the top of my head that would really 
be meaningful and useful to most people...

> O  idle current draw

Well, from what I've seen, idle current draw/power consumption usually 
has a very small effect on range. At any rate, how would you determine 
the value of this number? Electric A/C and heat (if installed) are 
relatively constant "idle" loads on the battery pack, but what about the 
load of the DC/DC converter? This will be highly variable, including 
being dependent on the size of the converter installed. So it sounds 
like to get even a close idea of "idle" power consumption you'd need to 
know a *lot* more information about the EV.

> Each electric motor type has a given speed/torque/current
> characteristic.  This needs to be matched to the vehicle requirements.
> The motor must develop the required torque at its rpm for the given
> vehicle speed.  The needed gear ratio for a given motor will vary
> depending upon operating requirements.  Incorrect selection will result
> in poor performance and should be reflected in the calculations.

Mechanical power P = ((Torque * Speed)/const.) What matters is that the 
motor is capable of producing at least as much power as the vehicle 
requires to travel at the speed you want it to, for as long as you plan 
on traveling at that speed. For a given power requirement, gearing takes 
care of any mis-matches between the motor's torque and speed verses the 
torque and speed at the vehicle's wheels.

> For example, operating an ADC FB-4001 directly coupled to the rear
> differential will result in poor acceleration.  Further, operating a
> Kostov only in first gear also result in motor overspeed at freeway
> speeds.  This should be indicated by the calculator, such as Uve's. 

Where does Uve's calculator indicate these things? For example, 
according to the calculator, 1st gear @ 90mph would require my motor to 
be spinning at 13,000RPM with 383 Volts to it... both of which would 
rapidly destroy my motor. Many of the results calculated in these motor 
speed/torque/etc. tables for 1st-5th gears are either not possible or 
disastrous just like these are. But the calculator doesn't show which 
values are the achievable/safe limits for the given setup. So why show 
these numbers? Doesn't it just increase confusion and decrease 
usefulness of such a calculator? Or am I missing something?

Thanks,

-- 
-Nick
1988 Jeep Cherokee 4x4 EV
http://Go.DriveEV.com/
http://www.ACEAA.org/
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