# EV Calculations

5177 Views 8 Replies 4 Participants Last post by  mattW
Here are a couple of simple calculations that a person can use to estimate range.

range[km]=250 x capacity[kWh] / (mass[kg]^0.6)
-or-
range[miles]=250 x capacity[kWh] / (mass[lbs]^0.6)

Obviously these calculations do not take wind resistance, drive train efficiency, rolling resistance, etc, but comparing these results to results from sites like EvConvert.com may give a good idea of what range to expect from various EV configurations.

Here is another good site for graphs and formulas of this type.
1 - 2 of 2 Posts

#### KiwiEV

· Registered
Joined
·
931 Posts
For those looking to calculate the maximum electric motor RPM in each gear, I recommend clicking on this RPM Calculator
This is essential for those not wanting to over-spin your motors.
The 9 Inch "FB1-4001A" motor from Advanced DC has a maximum RPM of 5600 RPM and without a rev-counter or reliable speed/gear chart memorised, it'll happily overspin and you won't hear it or notice it until it goes pop. That terrifies me a little.

#### KiwiEV

· Registered
Joined
·
931 Posts
I hear ya. The Tredia has a tachometer and I think I've figured out a way to make it work on a Curtis controller that doesn't support tachometers.
I've rewired the back of the dash and found that 1.5 volts displays just over 4000 RPM.

This means in theory by using a variable resistor (for tweaking) and a very small generator on the tail shaft of the motor, I can send small voltages through to the tachometer relative to the speed of the motor.
It's crude but it could work with tweaking.
It means I can avoid purchasing and installing an expensive optical sensor to measure the tailshaft RPM and feed it in pulses to the tachometer. That's the professional way apparently. I prefer my idea.
I wonder if it'll work?

Here's me experimenting the other night:

1 - 2 of 2 Posts