From: howard.smith@spacebbs.com (Howard Smith)
Newsgroups: sci.energy
Subject: Re: electric fuel gauges
Date: 21 Dec 92 23:17:00 GMT
Reply-To: howard.smith@spacebbs.com (Howard Smith)
Organization: SPACE BBS - Menlo Park, CA - 10 Lines + 4gB - 415-323-4193

CJL>Oh?  The performance of NiMH batteries doesn't change as they age  (shades
CJL>Oliver Wendell Holmes's Fabulous One-Horse Shay!)?  They're not affected by
CJL>temperature?  Driving cycle (i.e., discharge rate) doesn't affect the energ
CJL>availability in an extremely complex way?

The efficiency of NiMH batteries at various charge and discharge
rates as function of temperature is fairly predictable if the batteries
have not been abused, but one doesn't really need even to know that. The
performance of any battery is a function of the charge and the internal
resistance which is a function of construction, temperature, age, etc.
The internal resistance as a function of discharge rate is easy to
measure. An ammeter and a two voltmeters fed into a simple calculator
with a few lookup tables can keep track of every thing and give you
a good estimate of how many miles at the present velocity the batteries
are good for, displayed on the dashboard. If you run out of charge, then
competency becomes an issue?

CJL>=The best way of preventing a low battery is to plug it in every night.

Well, I was just pointing out that the weekly trip to the gas station
will be a thing of the past. It will be easy to keep your batteries
charged. Hughes has designed the plugs and SoCalEd is installing
prototype charging facilities in homes and at their facilities.
Petitions are before the Utilities Commission for special rates for
off-hours charging. They have even designed a parking meter with
charging facilities which takes credit cards. Places to charge batteries
will probably be more prevalent than the now disappearing gas stations,
but even then some will run out of charge.

CJL>Er, Howard? Suppose you've got a nominal range of 60 miles. You've
CJL>driven 55 miles. You're driving past a place where you could
CJL>recharge your battery, you *REALLY* want to get to someplace about 5
CJL>miles further in the next half hour.

CJL>Do you stop and recharge your battery, or do you keep driving?

CJL>How the hell does whether you recharged your battery last night or
CJ>not make difference here?

Well, if you can keep it charged and your range is greater than your
commute, then you have nothing to worry about. Keeping it charged up
will also make it last longer. The problem you have cited of running
on an empty tank also exists with gasoline and ICs, I believe.

It seems to me this present thread about EVs started sometime ago with
someone who had a twenty mile commute.

CJL>=Saves all that wear and tear of going to the gas station and
spilling gas on your shoes.

CJL>Why didn't I figure out before now that you're not competent to be
a fillin station attendant?

Filling station attendants? The stations I go to only have cashiers.
Attendents seem to be extinct around here, but things may be different
in rich, smoggy Pasadena.

You only learn to avoid getting gas on your shoes when you stop trying
to top off the tank. So there, I am capable of learning a thing or two.

Happy Holidays!

hhs, electronics engineer, and I know how to spell it.
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Newsgroups: sci.energy