Regen Braking Efficiency

[kuzzi]

So I understand the concept that the motor turns into an alternator while braking.

 

Just wondering what the efficiency of the motor/generator/alternator was going to stored energy in the battery.

 

No alternator is 100% efficient, yet we can get 100% regen braking score. So if the motor had a 70% efficiency of turning our kinetic energy back to electrical and the batteries had a return efficiency of 50%, would a 90% braking score correlate to 31.5% (.90*.70*.50) of our kinetic energy converted back to stored energy in the battery? These values are just arbitrary, I do not know how efficient the batteries are at absorbing this alternator energy.

 

If this is the case, then the braking score is calculated based on the total amount of energy that can be absorbed by the battery at the time rather than the total amount of kinetic energy we had at the time of braking.

 

Is this correct?

[murphy]

Nothing so complicated.

The brake score is based on how much of the available regen energy is returned to the battery versus how much is wasted by the friction brakes. If you can bring the car to a stop without applying the friction brakes at all until the wheels stop turning the score will be 100%.

[kuzzi]

So what is the limiting factor of regen braking?

 

Under hard braking, would the motor generator be able to apply a large enough load to slow the car to a stop or is it just too weak?

 

Would this cause too much strain on the electrical systems affecting longevity, thus the need for friction brakes?

 

My curiosity gets the best of me sometimes.

[kuzzi]

Nevermind, read this thread fully:

 

http://fordfusionhybridforum.com/topic/5491-how-do-you-get-maximum-regenerative-braking/?hl=braking

 

Load provided by the generator is determined by the computer based on multiple factors, including temperature, recharge rate, etc.

[acdii]

If you can slow down on regen until just a hair under 5 MPH before the service brakes apply, then you can get 100% score. It seems like 5MPH is the magic number when the circle disappears and service brakes kick in.

[hybridbear]

So I understand the concept that the motor turns into an alternator while braking.

 

Just wondering what the efficiency of the motor/generator/alternator was going to stored energy in the battery.

 

No alternator is 100% efficient, yet we can get 100% regen braking score. So if the motor had a 70% efficiency of turning our kinetic energy back to electrical and the batteries had a return efficiency of 50%, would a 90% braking score correlate to 31.5% (.90*.70*.50) of our kinetic energy converted back to stored energy in the battery? These values are just arbitrary, I do not know how efficient the batteries are at absorbing this alternator energy.

 

If this is the case, then the braking score is calculated based on the total amount of energy that can be absorbed by the battery at the time rather than the total amount of kinetic energy we had at the time of braking.

 

Is this correct?

Brake score is % of potential energy recovered. This thread helps explain a little bit about the efficiencies. I have some more ideas I want to add to that topic whenever I get time to express them in words. Your assumption above about multiplying the brake score times the efficiency of the regen process times your kinetic energy will tell you how much energy was put back into the battery.