Thursday, July 17, 2014

500

A milestone or is it a kilometer-stone...

With the odometer working, it is much easier to see total electric distance.  Well today, Jane hit 500 electric-KM.
This is significant since it has been 500KM without a mechanical issue.  Next goal.... 1,000KM

Electric-Regenerative Braking

One of the interesting characteristics of electric cars is their ability to recapture some of the energy that would normally be lost to braking and use it to recharge the batteries.  A key reason to use an AC (PMDC) motor is they are ideal for regenerative braking.  Previously, the regen function was set in the Kelly Controller (KHB 72701) to start when the gas pedal was released.  However, with the desire to be able to shift gears while rolling (and the lack of clutch), I realized that if the motor was braking, it put back-pressure on the drive train which made shifting impossible.  Also, the brake lights would not illuminate while regen was active which may have been confusing for other drivers, since Jane was slowing but no brake lights were on.

The Kelly controller supports having Regen start upon the grounding of the brake-sw signal.  So a simple 12V relay and a few wires later, the brake-sw signal is now grounded when the brake-lights are activated by the brake pedal.   This give the driver complete control.  To coast or shift, simple take your foot off the gas and the motor free-spins.  Shifting from 2nd to 3rd or 4th is easy since the motor has little momentum.  When the brake pedal is pressed the controller turns on regen braking and starts to put charge back in the batteries.  The braking is currently set at a 15% current limit or about 105 amps.  This results in soft braking right as the brake pedal is pressed and before the mechanical brakes start to engage.

The Arduino Mega digital dash reports that initially ~1200 watts are being generated through regen and this decrease as the car slows.  @ 15% the onset is not too jarring yet the rate of deceleration is reasonable for city driving.  This will save the mechanical brakes and provide a little charge back to the batteries.
A small code addition to the dash added a counter to display total watts from regen along with total watts from normal driving.  This will provide some information about of the range benefit from regen.

1 comment:

Bradley King said...

well done so far man