[ausev] EV Calculator Script

[Charles Birkhead]

The motor characteristics must be considered.  The motor characteristics
determine its maximum torque vs rpm.  For a given vehicle speed (and
resulting motor rpm), the max motor torque (supply) must be greater than
the drag force torque (demand), and the battery voltage must be greater
than the motor voltage. 

Also consider the voltage drop due to internal wiring and connections.
Each connection has a finite resistance.  The total resistance from
connections can be significantly greater than that for the wiring. 


-----Original Message-----
From: ausev-bounces at austinev.org [mailto:ausev-bounces at austinev.org] On
Behalf Of Nick Viera
Sent: Thursday, January 04, 2007 11:53 PM
To: AustinEV News Announcements and General Discussion
Subject: Re: [ausev] EV Calculator Script

Hi Mark and all,

Mark Hastings wrote:
> There is a section on Uves calculator where it lists the max speed in
> each gear and whether it is RPM or voltage limited.

Right, I did see that. Unfortunately that section fails to list the most

important limiter of max. speed: available battery power. For example, 
Uve's calculator tells me that I can go 77mph max. in 3rd gear with 
battery *voltage* being the limiting factor. I know from real life that 
this is not true; and that my max. speed is actually around 64mph with 
battery *power* being the limiting factor (unfortunately) :-/

My EV-RATS script calculates and shows an EV's top speed not by doing 
simple gearing-RPM calcs but by taking the maximum available power from 
the battery pack and back solving for how fast you can travel 
(regardless of gear), still having enough available power to overcome 
all sources of drag (aero drag, rolling resistance, etc.). I think this 
makes it more practical and useable. Comments?

> The further sections where it shows 1st gear at 90mph and shows
> speed/draw/etc are confusing but if they were somewhat accurate it
> would be useful. If I was to make one easy change to those
> 1st/2nd/3rd/4th/5th gear section where it shows speed/draw/etc at
> each speed it would be to put N/A in all the speeds that weren't
> available in that gear.

Agreed! That's the minimum that should be done to make Uve's 
calculations more applicable to a given vehicle.

> I tried the new calculator and it showed my S-15 pickup getting
> 18miles. Which is a little low unless it is winter but I probably
> don't have all the figures properly set for the vehicle.

Hmmm... okay. All the feedback I've gotten so far indicates that this is

the case (EV-RATS being overly pessimistic about range). I'm trying to 
figure out if this is due to calculation error(s), or if user's aren't 
putting in accurate variables for their EV's, or ??  Could you give me 
an idea of how far off its range calculations are for your vehicle and 
what Cd, Coefficients of drag and rolling resistance your using?

> That was another nice feature of Uves calc where it had templates for
> some base vehicles. Perhaps including some links to sources where one
> could easily find that information would be better then templates.

I'd love to do this, but it seems like a really really laborious task 
given all the different types of components and vehicles out there. Not 
to mention that it would be hard to guarantee the variables (esp. for 
batteries) wouldn't change and then the template(s) be incorrect at a 
later date. Maybe a good compromise would be to make it possible for 
users to upload their numbers to files that EV-RATS can load, e.g. 
creating a database of "user submitted templates" for the calculator?

Thanks for the input!

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