# AC System design considerations

Not sure if it’s much different from a DC system in terms of the basic considerations, but I was wondering if anyone could point me to a good reference for figuring out how to calculate acceleration(estimates of course), range, etc. based on weight, motor type, controller, battery pack, etc.

I know that this is not easy to do in general because of the many factors that change between conversions, but I would just like to read something on the basics of how each of the above mentioned variables affect each other.

I know this is a little general for a thread topic, but one specific question I could posit is:
Does the pack voltage directly correlate to acceleration, for any motor?
Does a more powerful motor mean more power with the same voltage, or just more torque?

Is there anyway to figure out before starting what the sweet spot is for your battery pack, that will give you best range and acceleration? It seems like it is mostly a function of V(battery pack voltage), W(total weight of conversion), and AH(total capacity to store energy). Has anyone figured out a rough formula for determining the relative “sweet spot”? Are there any significant variables left out here?

A lot to cover in a single thread but hopefully it will garner some discussion.

thanks

…You have at least one big factor left out-- namely current.

Here’s how it works: The more Voltage you put through a motor the more Current will flow also. The Power going into the motor is Voltage X Amperage.

Motor output (in W) = V * A * [motor efficiency]

As a rule of thumb, in the quarter-mile (a good measure of acceleration) 1 HP electric is about equal to 3 HP gasoline. This being said, there is about 1.3 HP in 1 kW.

So if your motor draws 800 amps at 144 volts, and your motor is achieving 80% efficiency:

Motor output = 144 * 800 * .80 = 92.16 kW = 119.808 HP

HP equivalent in the quarter-mile:

359.424 HP (IC)

Another note about current (amperage) is the more current you draw from the batteries the less efficient they are, shortening your range with respect to the size of the battery.

So if I increase the system pack voltage, how will that effect performance/acceleration? Will efficiently go down? Or up? Is the power of the motor proportional to the system pack voltage? Or, is it strictly dependent on the controller you use?

I looking at the Azure Dynamics AC24LS/DMOC445 combination for a mini-truck conversion(curb wt.=2150lbs). Anyone know what a good pack voltage to get a decent pickup from a red light? It sounds like most people who choose a 144V(w/ 8Vs) pack aren’t happy with the acceleration.

I would like the same acceleration I get with my '96 Toyota Corolla ICE car. It doesn’t have to be a race car, but I don’t want to hold up traffic much.

On another note, is there a general formula for figuring what kind of power consumption you can project for acceleration, cruising speed at 35mph, etc. Of course wind drag is probably the hardest thing to calculate, and tire friction since there are so many types of tires. But are there ways to estimate these figures?

Thanks for the reply, good information to consider.