Explain regenerative brakes

[Scrooge2]

what kind of performance do these electric engines turned generators offer? Do they stop the vehicle well? How do you control how hard the braking is? Just questioning the reliability of this method.

Anyone with some expertise or even own a hybrid, please share your experience!

 

[Slick5150]

Regenerative braking doesn't affect the brakes themselves. When you hit the brakes, it just turns the electric motor into a large generator (more or less reversing its function) and uses the momentum of the car as its energy source. It feeds that energy into the batteries which helps keep them charged.

 

[Mark R]

They will brake the car only relatively gently in current cars - although they could be tweaked to brake almost as hard as they can accelerate.

You use the brake pedal in the normal way - and for the first inch or so of movement, the regenerative braking will be active. The computer will control hard hard the motor pushes depending on how hard you press the pedal - in the same way as it will control acceleration.

Press harder, e.g. for an hard stop, and a normal braking system activates as well.

 

[DrPizza]

I've always wondered (and perhaps someone attracted to this thread could point me toward the answer) - car batteries can't hold an unlimited amount of energy. Where does the energy go when the battery is "full"? Doesn't the act of driving the car itself charge the battery, keeping it toward its maximum potential?

 

[nakedfrog]

Originally posted by: DrPizza
I've always wondered (and perhaps someone attracted to this thread could point me toward the answer) - car batteries can't hold an unlimited amount of energy. Where does the energy go when the battery is "full"? Doesn't the act of driving the car itself charge the battery, keeping it toward its maximum potential?

I would imagine there would be a circuit in place to disengage the charging once the battery reading hits a certain point.

 

[Mark R]

I think in the case of hybrid cars the battery is never allowed to get 'full' - it's held at about 45-60% charge (at least that's how I think the prius does it).

If the battery charge rises above 60% then charging via the gas engine is disabled (and the gas engine only runs when the car is moving at speed). If the battery charge drops below about 45%, then the gas engine is started to charge the battery. If you still manage to discharge the battery by agressive driving to below about 40%, then the ECU will disable electrical assistance (or severely cripple it) until the battery charge comes up to 'normal' levels.

The 60% headroom gives plenty of capacity for regenerative braking, which on current hybrid cars isn't particularly effective anyway. Whether there's a point above that which disables regenerative braking, I don't know. Electric trains frequently use regenerative braking, but they do have a resistor bank which can be used to dump the energy if the grid won't accept it.

 

[newmachineoverlord]

Mark's answer is pretty much correct. In order to get the charge level above 75%, you would have to use some sort of 1337 going down a mountain hax. Even if you used such a haxoring, there are still hydraulic brakes on the vehicle which can be used to handily convert excess kinetic energy into useless heat. Oh, and going down a mountain would likely be preceded by going up a mountain, at which point there should be some way of getting the vehicle to expend battery power. Hopefully someday the engineers will make it smart enough to detect a gradient and respond appropriately by using more battery power when going uphill, in anticipation of going downhill later. This doesn't really matter to me, since I live on the plains, not the red mana generating regions.

To the OP: Regenerative breaking is about 31% efficient at capturing energy. It is a great method at slowing down a vehicle from high speed, as there is no physical wear due to friction. Thus your brake pads don't get hot, and are less likely to warp. The fact that it saves wear on the traditional braking system ultimately makes the brakes more reliable than a traditional car. Also consider that here you have a dual system, and both would have to fail at the same time in order for you to not be able to brake as needed. Electromotive braking has been used for trains extensively, and the power is either fed back to the grid or dumped in resistors.

http://auto.consumerguide.com/Articles/...icles/article/FA_hybrid_batteries.html
"To get maximum life out of the Prius battery pack, the car's computer brain does not allow the battery to fully charge or discharge. Toyota says that for the best service life, the Prius battery likes to be kept at about a 60 percent charge. In normal operation, the system usually lets the charge level vary only 10-15 percentage points. Therefore, the battery is rarely more than 75 percent charged, or less than 45 percent charged.

If you're familiar with the Prius, you know there's a battery-charge indicator on the instrument panel. Toyota says this isn't the charge level per se, but rather a state-of-charge window. The top of the window represents about a 75 percent charge, the bottom about 45 percent charge.

According to Toyota, the life of the Prius battery pack is determined more by mileage than by time, and it has been tested to 180,000 miles. Supporting this are first- and second-generation Prius taxis in Canada that have reportedly traveled more than 200,000 miles without suffering any battery problems."

 

[walkur]

/OT

😀 at the "red mana generating regions."