The EV modeling program

helps battle complexities of batteries, weights, Peukert Effects etc

The very simple, user-unfriendly C program, ev.c, is driven by a user request to design a 3 or 4 wheel vehicle which will travel a given range at a given speed. Ev.c considers each appropriate battery model, asking itself how this battery might be used in meeting the stated goals. The report on each user request is a web compatible table where each line of the table corresponds to a battery model considered. Marginal results are color-coded yellow; worse results are colored red.

Input

You define a desired EV's requirements:

how far must it go?
at what cruise speed must it travel?
how many wheels does it have? (3-wheelers are less constrained by DOT rules but are supposed to be under 1500 lbs)
what is its Cd (Coefficient of aerodynamic Drag)? See table.
what is its cross sectional area?
what is the RRC of its tires?
what is its empty weight, before pax, motor, and batteries added?

The battery information is built into the program at present. It is a superset of the information used to document these web pages. It is called, simply, The Battery Table.

Output 'banner'

Sample output can be viewed here. A short summary of the car in question is given just before the table is shown.

'mazda12v', empty 2000 lbs, $5000, +driver, motor, no batts 2335#
Cd 0.35, Area 20 sq ft, RRC 0.0120, steer'g/brake drag 0.0030
requesting 55 mile range at cruise of 60 mph
Proj cost includes $500 charger for LA or $2000 for BMS if not LA
Ev conv kit $2500 if <= 8hp, Thunderstruck
Ev conv kit $6400 if  > 8hp, KTA

Output columns

	LA (Lead Acid), AGM, LI (Lithium Ion)
	Battery's model name
	nominal voltage
	nominal amp-hour rating
	weight in lbs. mount not considered
	Depth of Discharge . Set in the battery table. Typically 80%.
	sum of all drag forces, lbs. more
	Watt-hours per mile at the requested speed
	Rear wheel horsepower needed to maintain requested speed on level ground.
	amperage needed to maintain requested speed on level ground.
	kilowatts needed to maintain requested speed on level ground.
	required Watt-Hours for requested range at requested speed.
	Peukert Efficiency at the requested speed.
	Required amp-hours of pack.
	pack voltage.
	number of batteries per 'string'.
	number of strings of batteries. ideal is 1.
	total number of batteries
	pack's weight, lbs. Does not include mounting hardware, cables.
	pack's portion of total vehicle weight, percent. Some texts say this should be 30% or larger for EVs driven by LA batteries.
	pack cost, dollars. Shipping, taxes, discounts not included.
	portion of req'd range met by this pack design.
	final range value, miles.
	total vehicle weight, w/ driver, motor, pack etc.
	total project cost, dollars. Some fudge factors are thrown in for BMS, misc costs. These values are probably only useful for relative comparisons.

The value cells are sometimes color-coded to indicate a problem. For instance, if the vehicle is described as a 3 wheeler and the final vehicle weight exceeds the DMV/CHP maximum for such, the cell will be colored red. When close to a threshold, it will be yellow.

Caveats

The program does not consider:

the effects of temperature on batteries. LA's, for instance, are best in the range of 50-80 degrees F.
extra weight of power assisted braking equipment.
extra weight of an on-board charger
project cost is only the cost to make the vehicle. no DMV
operating costs and cost-to-own are not calculated.
If more than one 'string' of batteries is required by a design, the cost and weight of handling multiple strings is not considered.
The Peukert Exponent used in the calculations is the one given by the manufacturer and this means that it'll be the initial value, when the battery is new. The calculation does not try to guess where that value will go to over time/use.
Hills are not considered in energy use calculations.
The excess power needed for acceleration is not calculated.
The energy lost to braking, as in stop-and-go traffic, is not considered.
gear ratio logic is being slowly added. At present it doesn't work.

file: REDSTICK/car/evDotC.html