Q&A
with TJ Byers
Electronics Q&A
In this column, I answer
questions about all aspects
of electronics, including
computer hardware,
software, circuits, electronic
theory, troubleshooting, and
anything else of interest to
the hobbyist.
Feel free to participate
with your questions, as
well as comments and
suggestions.
You can reach me at:
TJBYERS@aol.com.
Good-bye 12 V, Hello
42 V
Q. How about some details (or an
appropriate website) about the
upcoming change in automotive electrical systems? I read somewhere
that the new bus voltage will be 42
volts. Is that 20 cells times 2.15 volts
per cell? What other interesting and
unique features will be implemented?
Will something like PCM be used for
switching appliances (lights, blower,
rear-window heater, etc.)? Any information or clues that you could pass
along would be very interesting and
most appreciated.
Joseph F. Richmond
via Internet
What's Up:
F
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The usual assortment
of requested circuits.
My favorites are the
soldering iron warm
down and low-battery
indicator. Discovered a
new reader hobby, and
spent a lot of ink on an
emerging technology.
NUTS & VOLTS
E
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y
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h
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n
g
Another reader comes
through with a tip, and
there are many Cool
Websites! to check out.
A. The new 42-volt automotive
electrical system comes as a
result of ever-increasing power
demands. Back in the days of old,
way before many of you were born,
six volts was the standard power bus
for autos. That's because the cars in
those days had almost no electrical
demands —- typically head/tail light-
ing and maybe a heater motor.
Somewhere in the mid 1950s, the
ante was upped to 12 volts. This
came as a result of a demand for air
conditioning, brighter headlights, and
higher-compression engines (which
needed bigger starter motors).
Today's cars really put a demand
on the electrical system with power
windows/seats, climate control, monster stereos, and window defrosters —
not to mention of what's up and coming: GPS, communications, PCs, on-board video, etc. It's no wonder the
12-volt bus is feeling the strain. It's
estimated that, by the year 2010,
some cars will require 10 KW of
power! That's enough to power a
home. To meet these demands, the
voltage has to increase. Why?
Because Ohm's Law says so.
Let's say you have a six-volt system
with a 10-amp load ( 60 VA) connected by a 0.1-ohm wire. Ohm's Law
says the voltage loss across the
wiring is one volt, making just five
volts ( 50 VA) available to the load —
a loss of 17%. If we up the voltage to
12 volts and reduce the current to
Figure 1
8
FEBRUARY 2004
