Path: utzoo!attcan!uunet!zephyr.ens.tek.com!gvgpsa!gold!grege
From: grege@gold.GVG.TEK.COM (Greg Ebert)
Newsgroups: sci.electronics
Subject: Re: Electronic Car Brakes
Message-ID: <1488@gold.GVG.TEK.COM>
Date: 24 Sep 90 18:48:28 GMT
References: <8581@ncar.ucar.edu> <1414@atlas.tegra.COM>
Organization: Grass Valley Group, Grass Valley, CA
Lines: 29


Although somewhat 'lo-tech', I remember some of the electric-powered mail
cars used high-speed flywheels (hence lower mass) for short-term energy
storage. The motivation for this was letter carriers who took their
vehicle on routes with curbside mailboxes, which entailed a lot of
start-stop driving. They were manufactured by Garrett (now Allied-Signal).

As someone mentioned, batteries tend to have rather long charge cycles.
They correctly mentioned that a capacitor would probably be too large to
serve as an energy reservoir. However, when HV technology improves, they
might be feasible. The energy stored in a capacitor is proportional to
the square of the voltage (1/2CV^2), but the volume (weight) of a
capacitor is more linear with respect to voltage (and capacitance), so
I would expect that using high-voltage capacitors might cut the mustard
for fast-braking. Some simple calculations:

Assume a 2000Kg vehicle (quite heavy ~4500lb) moving at 33 m/sec (~70MPH).
The total energy is about 1 megajoule. At 10,000 volts, you could dump
this into a 20,000uF capacitor.

Imagine tapping into this when you stomp on the accelerator !!!

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