Regeneration question

[GadgetGav]

A motor that is being turned becomes a generator, this much we know. The e-Golf makes use of that for regenerative braking and for recharging the battery when you're in D1-B modes, but what happens in straight up D mode? When you lift off the accelerator, the power needle sits at zero but you're still moving along, so where is that generated energy going?
Is there a clutch that disconnects the wheels from the motor, so nothing is being generated?
Is energy being generated but dumped into a big resistor?
Does the DC-DC converter include a dummy load resistor and that's one of the reasons it's water cooled?
What ever the mechanism, it must have to happen when the battery is full too regardless of the mode setting...

Does anyone know how it works?

 

[Stretch2727]

No clutch or any mechanical disconnect. This is the beauty of an all electrical car.

What occurs is the controls put the battery load on the "generator" which creates the mechanical resistance to slow the car. The varying levels of regeneration are just adjustments by the electronics to put load on the "generator" and charge the battery. It really is just working backwards from when the car accelerates. The more electrical current from/to the battery the more power/generation from the motor. The motor generates higher levels of electrical current at high levels of regeneration and more battery charging. Of course you are slowing faster so the kinetic energy of the car is lost more quickly. Zero regeneneration is zero load on the motor so it is freewheeling just like if you spun a electric motor that was not plugged into anything. It cannot generate a current (and mechanical resistance) unless it is hooked to an electrical load.

If the battery is fully charged regeneration will be shutdown at some point as there is no place for the current to go. The car will freewheel and you will need to use the mechanical brakes. I am not sure exactly at what point this occurs on the egolf but I know most electric cars (including tesla) do not regen if the battery has 100% or excessive charge.

I use the drive in highway situations. You do not want to be accidently alternating between power and regeneration in constant speed situations. There is alway in efficiencies so a percentage energy is lost. On secondary roads where your speed almost always needs to vary using the higher regeneration modes insure you are maximizing regeneration. When you use the brake in drive mode you may unknowingly engage the mechanical brakes.

One other comment. Reverse is not another gear. The direction of the motor is electrically reversed so you can go backwards. In theory you could go just as fast backwards....but I am sure there are software limits to prevent this.

Hope this helps....