Re: 42 Volt Electrical Systems

["Raymond Vacha" <ray_vacha@xxxxxxxxxxxxxx>]

Scott Miller comments: <snip> BMW CCA member Larry Ayers is a physicist who
specializes in lighting.   He gave me permission to share this with you:

> ...yesterday, I decided to venture down to the SAE Lighting Committee
> meeting in Monterey (well, actually Seaside).  Among other things,
> they  mentioned that starting in 2002, some cars will have a 42 volt
> electric system (some proposals would retain a 12 volt system for
> lighting).  By 2010, commentors expect all cars to use 42 volts.  The
> rational is to decrease the size of alternators and wiring harnesses;
> Ford said that right now that have maxed out alternator size for some
> vehicles at 135 amps.

I didn't ask Larry how they came to choose 42 volts, as opposed to some
multiple of 1.5 volts as we are used to with batteries, but then I'm not an
electrical engineer.  I expect we'll be seeing more on this in the
future.<snip>

This is really not old news - the concept has been kicked around for several
years now but has gained a lot of steam since about April or so.  The basic
issue is that alternators are close to being maxed out while an average
car's electrical load is expected to explode in the coming years.  The
increased demand for electrical power will come from a wide variety of new
technologies being developed including electric solenoid-actuated valves
(good bye cams...), electric fly-by-wire steering, motor-driven turbos
(really!), water pump motors, brake-by-wire, electrically heated catalytic
converters, air conditioners (really!), and the mobile office (phone, FAX,
video, automobile networking, etc.) to name a few.  By increasing the
system's voltage, the required current goes down, resulting in
simplified/lower cost wiring harnesses and smaller wire gages.  Why 42V?
Lower voltages don't reduce the currents enough to justify the effort while
higher voltages present safety and regulatory issues, specially in Europe.
Believe it or not 42V supposedly came from the fact that it is a multiple of
12 (12V times 3).  Of course, today's autos nominally run at 13.8V, not 12V,
so this seems a tad bit odd.  Adoption of 42V opens the door for one more
interesting technology - the combination flywheel/alternator/starter motor.
A committee has been formulating the system level concepts and includes
Ford, M-B, BMW (how's that for content?), and others.  I've also heard that
the first 42V auto will be a model year 2002 launch, but the only thing I've
seen in writing claimed that M-B has committed to 42V for the model year
2005 S class.  Technically speaking, the only thing that shouldn't be
powered from 42V is incandescent lamps, which exhibit drastically reduced
operating life at higher voltages.  Will 12V stay around?  IMHO, yes, but
only for powering "legacy" devices (radar detector, cell phones, etc.)  Will
42V cause the auto manufactures to switch to HID lighting across the board?
Will other lighting be accomplished by piping fiber optics around the car?
Only time will tell.  Comments welcome.

P.S.  Physicists working on lighting are probably working on technologies
past HID!  Can you share with us?


Ray Vacha
97 E39 540i 6 Speed "ZEIT"
BMW CCA, NMA
Northern Ohio Chapter
mailto:ray_vacha@domain.elided

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