Path: utzoo!attcan!uunet!samsung!zaphod.mps.ohio-state.edu!swrinde!ucsd!ucrmath!sisler!stebbins
From: stebbins@sisler.ucr.edu (john stebbins)
Newsgroups: sci.electronics
Subject: Re: Electronic Car Brakes
Message-ID: <8836@ucrmath.ucr.edu>
Date: 24 Sep 90 04:12:32 GMT
References: <8581@ncar.ucar.edu>
Sender: news@ucrmath.ucr.edu
Reply-To: stebbins@sisler.ucr.edu (john stebbins)
Lines: 29

In article <8581@ncar.ucar.edu>, cook@stout.atd.ucar.edu (Forrest Cook) writes:
|> 
|> >[ lots of interesting stuff about electric cars and relative efficiencies ]
|> .
|> Instead of saying it can't be done and then whining when the Japanese
do it :-) 
|> ....
|> How about electric car designs that brake by using the motor to charge back
|> into the batteries?  Such a system could probably save several tens
of percents
|> in efficiency, especially for city drivers.  Are there any special tricks
|> involved in doing this?  I can see how it would be possible to slow down
|> by connecting higher voltage windings from the motor/generator to the
battery,
|> but is such a system able to come to a complete stop and use all of the
|> braking for recharge?  Perhaps a PWM system would do most of that.

There are a couple of problems you didn't address.  First is batteries
charge slower by a factor of 10 or more than they discharge.  Second
is that most people break much faster than they accelerate.  This compounds
the first problem.  I haven't calculated the amount of energy that is 
involved here so this may be absurd, but I was thinking that a whopping big 
capacitor may take care of part of this problem and have the side 
benifit of giving you more readily available energy for your next
acceleration.  The phisical size of such a capacitor may be larger than
the proposed vehicle for all I know.  Its just a thought.

John Stebbins
stebbins@ucrmath.ucr.edu