Regenerative Braking Refinement

After a little experimenting, the regenerative braking settings seem to be dialed-in.  Currently, the Kelley KHB 72701 controller is set at 10% braking upon throttle release and 25% braking upon brake switch activation.  The brake switch is wired to the standard brake lights so a slight touch of the brake pedal will raise the braking power limit to 25% from 10% when the gas is released.  This % is the percent of the controllers maximum current (700A).  So far I only observed a maximum of 1500 watts of regen power and that only lasts for a few seconds before the car has slowed.

These settings provide reasonable engine braking and normal braking levels for coming to a stop.  It seems the braking power is proportional to the speed which makes for a smooth braking experience.  Since the voltage generated by the motor is proportional to the RPMs of the motor, as the car slows, the voltage drops reducing the amount of current that can be generated by the motor-controller.

The 10% throttle setting also allows the braking to come on slower than jumping right to 25%, which was jarring.

The Arduino on the dash is now reporting both power consumed (watts x time) and regen power.  It looks like with my normal city commute, regen is providing about 5% back to the batteries. Not a lot but with a 25 mile range this is maybe a mile extra for a full charge.  I guess regen is really more psychological and mechanical brake-saving than real range extension.  It is a fun thing to talk about...

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.