Hi Darryl,
That was quite a read. You've done more research than I have on the subject. I've been relying more on my own analytical/theoretical skills rather than my own experience or the experience of others.
I think we're pretty much on the same page though. Your comments on gravity make sense but, I think we can agree that on some hills, you risk getting a Darwin award if you don't brake.
Wind drag is always a loss that cannot be regained through any means (that I know of).
I think we can also agree that regenerative braking is a function of how often one accelerates and decelerates by means other than those provided by ones environment (i.e. gravity). Sure, I can see driver training as a way to increase efficiency but, depending on where you're driving (this is the where it gets sticky), some terrain makes braking a must no matter
how much training you have. I can easily imagine an argument between someone in the Southwest and another in the Northeast U.S. disagreeing on the virtues of regenerative braking.
- Redler
[EMAIL PROTECTED] wrote:
[EMAIL PROTECTED] wrote:
Nuts, got bounced again.
Mike Redler wrote:
> Darryll,
>
> you wrote: ?Personally, I like the Advanced DC motors. But then I think
> regen is over-rated. If you learn to drive so that you use the brakes as
> little as possible, then regen offers little advantage, for there is
> little braking energy for it to recoup. Good strategy for improving fuel
> economy in ICE vehicles too.?
>
> As we discussed earlier, the advantages of replacing an IC motor with an
> electric motor exist with conditions that require constantly changing
> demands for power - demands that the IC motor can?t closely match. Those
> conditions include frequent acceleration and deceleration. The
> advantages of regenerative braking exist under exactly the same
> conditions. So, if your statement is true, you can?t suggest that less
> braking causes regen to have little advantage without also suggesting
> that electric motors have little advantage under the same conditions.
Actually, I can suggest electric motors have significant advantage in
this scenario, and I do. It comes from the physics of acceleration vs.
deceleration for road vehicles, and driver behaviour.
The following assumes level ground as an approximation that on average
most vehicles start and end their daily cycle at the same place, a
parking spot or driveway.
When accelerating from a stop, the vehicle has to overcome inertia,
rolling losses and aerodynamic drag. When decelerating, the vehicle
only has to overcome a (significant) fraction of inertia, as rolling
losses and aerodynamic drag are already braking forces. The secret is
coasting, allowing the rolling losses and aero drag to do as much of the
braking as possible. Gravity can also provide an effective braking
effect under the right circumstances. Accelerating from a stop is
essentially the only time the ICE engine is operating outside its design
range, because it would stall. Everything other speed should permit the
ICE to operate in its efficiency range via changing of gears, the
extreme version being the CVT which is slowly gaining in popularity.
Accelerating from a stop is where the series-wound DC motor really
shines, developing maximum torque at zero RPM.
I am only aware of one study that actually determined the benefits of
regenerative braking in real-world conditions. That was in the 1970's
by the USPS. Using their regular drivers, they put Gould electric Jeep
conversions on regular delivery routes. That's a lot of stops and
starts, which should be ideal for regen. They enabled regen on some
vehicles, and disabled it on others. The difference in range was about
8%. (I only ever saw this report once, and in hardcopy format. It
belonged to the Electric Vehicle Association of Canada, and I have no
idea how to find it now.) The cost of implementing regen on most EVs is
substantial. On some AC drives, it is "built-in", but those systems are
considerably more expensive than typical DC drives to begin with. For
most EVs, adding 10% more battery will provide more range advantage than
regen, for a lot less money.
Training drivers to drive for fuel economy requires no modifications to
the vehicle, and can achieve gains of up to 30%.
There are anecdotal reports that batteries last longer, and performance
is better throughout the drive with regen. This is mostly attributed to
developing a surface charge on the batteries. That may be unique to
lead-acid batteries.
So, get in your EV, accelerate from stops like a maniac, then coast to
the extent possible, and let the environmental braking forces do most of
your braking (rolling resistance, aero drag, gravity). If you only use
the brakes to hold the vehicle after it coasts to a stop, there is no
energy available to be collected via regen. It amazes me how often this
technique permits me to avoid stopping at traffic lights. Because I am
creeping up on red lights, they have more time to change without forcing
me to come to a complete stop. It won't work in every circumstance
(notably when stopping at the bottom of a hill), but with practice, it's
amazing how often this works. Yes, there is still some potential
advantage to regen, but not much. Spend some time in a hybrid like the
Prius or Insight. Consider how small the energy storage in their
battery packs is. Then look at what a small fraction of that is
actually provided in a regenerative braking situation.
Anyway, that's my case for how an electric motor can be superior for
acceleration performance, without leaving much opportunity for gain from
regenerative braking.
Speaking of regen and hills, I meant to respond to Zeke, but I appear to
have misfiled his message. The catch to your scenario is that most of
your regen opportunity will be occurring when your batteries are already
full (leaving home), and providing no benefit because no more
electricity can be stored. At the end of the day, when you're nearing
home, you could use that energy, but none is being generated as you are
going uphill. Unless I misunderstand the scenario you were describing.
Darryl
>
> -Redler
>
> Darryl McMahon wrote:
>
>>Personally, I like the Advanced DC motors. But then I think regen is
>>over-rated. If you learn to drive so that you use the brakes as little
>>as possible, then regen offers little advantage, for there is little
>>braking energy for it to recoup. Good strategy for improving fuel
>>economy in ICE vehicles too.
>>
>>An Electrek - wow that takes me back. So ugly they were cute. How's
>>the body (plastic I think) holding up after all these years?
>>
>>Darryl
>>
>>
>
> [snip]
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