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  1. #1

    Hybrid cars, recharging the batteries

    Mr. Bradley Berman, editor of hybridcars.com, wrote:

    <<Auto engineers have developed an ingenious system known as regenerative braking. Energy usually lost when a vehicle is slowing down or stopping is reclaimed and routed to the hybrid's rechargeable batteries. The process is automatic, so no special requirements are placed on the driver.>>

    Actually, the batteries are charged most of the time by the electric motor, powered by the gas engine and functioning as a generator.
    Only about 30% of the braking energy is regenerated. The rest is wasted as heat. Regenerating the braking energy accounts for perhaps 10% of the total used to recharge the batteries, unless one is driving downhill and braking most the time.

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  3. #2

    Hybrid cars, recharging the batteries

    Dorin, is your opinion based on scientific experimentation or observation on your part, or on a published article? If it's the latter, please share the URL of the article. If it's the former, it sure disagrees with my observations of my 2003 Honda Civic Hybrid (on which I have put over 96,000 miles).

    My not-precisely-scientific observation of my car with my driving habits is that about 50% of my battery's charging is from "engine deceleration" - letting off the accelerator slows down the car and charges the battery. Another roughly 40% is from hitting the brakes, and less than 10% is from the engine actively charging the battery.

    Where did you get your data?

  4. #3

    Hybrid cars, recharging the batteries

    I think it mostly depends on what your driving circumstances are.

    I drive mostly freeway so it's likely that my engine alone provides +50% of recharge.

    On the other hand if I drove with alot of stops then coasting charge and brake regen would definetly play a larger role.

  5. #4

    Hybrid cars, recharging the batteries

    Just found this link:
    &lt;&lt; Even at that low level of use, in a typical mixture of highway and around-town driving, regenerative braking can recover about 20 percent of the energy normally wasted as brake heat&gt;&gt;


    under "Itís elementary" title

  6. #5

    Hybrid cars, recharging the batteries

    The links below also provide useful info:

    &lt;&lt; Less than 20% of the energy of gasoline is actually used to drive the wheels of the car; most of the rest is lost as waste heat. In a conventional car, the engine is much more powerful than required to drive the car at a constant speed of say 100 km/hr because extra power is needed for accelerating the car in a reasonable time. Except when accelerating, this power is not really used, and most of the time, the engine operates inefficiently far below its capacity. The main losses of energy occur when the car is idling, braking, and driving at low speeds.&gt;&gt;


    &lt;&lt;Additionally, the electric motors of a hybrid vehicle can recover part of the braking energy that would otherwise be lost as heat in the brakes. They become generators, slowing the vehicle by using its kinetic energy to make electricity that is stored until needed. Some experimental vehicles have demonstrated up to 70-percent peak energy recovery, but recovery of about 50 percent is seen by many experts as a more realistic goal.&gt;&gt;


  7. #6

    Hybrid cars, recharging the batteries

    Dorin, you're mixing apples and kumquats above. The MotorAge website you noted says "the energy efficiency of the most modern production car is still less than 20 percent. Most of the energy used to move the vehicle at any speed over any distance is literally thrown away as heat. About half of that wasted energy goes through the brakes." No argument there, as the energy to speed up a car without regenerative braking is _all_ wasted when the car comes to a stop.

    My point is that in addition to using the vehicle's braking system to recharge the battery, simply letting up on the accelerator pedal also recharges the battery, as this action also causes the computer to engage the generator. Every time you let up on the accelerator, the battery is charged - every time you step on the accelerator, the battery is discharged into the generator, which now becomes an electric motor, putting that otherwise lost energy back into speeding up the vehicle. My contention is that this moves at least as much if not more energy back and forth than actual braking.

  8. #7

    Hybrid cars, recharging the batteries

    There are also ways to drive for maximum regen that differ depending on the vehicle. I drive so that I normally only use friction braking at ultra low speeds where regen doesn't take place anyway (the system determines this). Other times I'm anticipating stops and slow-downs, using low "gear" setting which applies stronger regen (while not touching the brake pedal). I can drive around a lot and then touch the brake discs... which are barely warm, if not cool!

    Previous poster is right, apples & kumquats.

  9. #8

    Hybrid cars, recharging the batteries

    The regenerative system is misleading because the brakes do not need to be applied to get regen. as Paul and Randy point out. This is the very reason why I use what I call the "fake shift" and "L" like Randy to recharge the battery. By letting off the acelerator and reapplying it slowly to maintain speed, the generator gets a big boost from the wheels to charge the battery. Repeating this till the battery is full is what I prefer. If you use the regen methods, you can cut back on the load of the ICE and get better FE.

    The FEH doesn't have an alternator to keep the 12 volt system including the electric power steering unit operating. Do some coasting in "N" while in EV and you will see how much regen plays a part in keeping the battery charge. Coasting or gliding in "N" stops regen and allows for a big increase in distance and maintaining speed. In my case with my driving habits, I'd say I charge my battery with regen about 70% of the time. My driving is more geared to EV and gliding in "N" as much as posible. Keeping up with battery demand with regen helps my overall FE.

    Most people would not use my driving style do to the effort I put into it. After discovering how to use the regen system, I'v had a big increase in mpg.

  10. #9

    Hybrid cars, recharging the batteries

    Speaking of MPGs:
    How do you determine the #s?
    I do not believe the number of gallons recorded by the pump is ever in our favor. How far are the numbers off?
    It very much possible that you guys are right and I am wrong. But until we have a way to count the amps and seconds for each source, it is a guessing game.

  11. #10

    Hybrid cars, recharging the batteries

    Dorin, I've checked my 2003 HCH odometer and speedometer several times with both a handheld GPS and with laptop-based GPS navigation software - they are both quite accurate. The numbers for MPG on the other hand don't work out quite as close but they're within 1 to 2 MPG - my first few tanks I did the math and had both higher and lower readings.

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