Power supply

[Frederic Breitwieser]

>I believe it would be simplest...and probably cheaper (maybe more
>reliable and safer) to purchase a 12VDC powered 120VAC inverter with
>enough capacity to run your PC.  It would probably run less than 100
>bucks.

Yes, this is by far the easiest solution, however the final rendition of
your PC-based ECM will require you to duct-tape this converter to the
firewall at some point :)

I have begun designing a switching power supply, much like the PC power
supply, to provide the +/- 5V, +/- 12V outputs.  I chose a switching design
for several reasons - linear devices (78xx and LM317T, etc) can generate a
lot of heat.  Heat sucks no matter how you look at it.  In addition, linear
power supplies operate by shunting the "excess" to ground, hence the heat.
This is a rather inefficient way to regulate power, however it does work
very well, can't argue with that.  I'm very slow at these things due to
being involved in a few zillion (okay, I exhaggerated, a few million)
projects at the moment, so feel free to design in parallel, and I'd be
happy to share what I've done so far.  I've basically leached a design from
a Radio Shack book, which I breadboarded "as-is" and got satisfactory
output.  My design is similar, just with much higher current capabilities.
I'm also trying to build in under/over voltage protection, so as long as
the input range is 9V thru 20V, the outputs will remain at their exected
voltage, just varying the intake current.  This allows the ECM to have the
right voltage no matter how many lights, starters, or electric motors are
going.

A little known fact, is *most* 486 and "weaker" system boards do not need
the negative power leads for anything other than the serial ports.  If you
don't need serial, well, you can get around this by playing with the "good
power" lead on the power supply.  I forget if this is grounded, or attached
to the 5V line through a diode - its been a while since I've experimented
in this fashion... but its doable.

Obviously, disabling your serial ports also disables an easy way of
communicating with your embedded PC ECM.

Anyway, sorry for the long post.


Frederic Breitwieser
Bridgeport, CT 06606

Homebrew Automotive Website:
http://www.xephic.dynip.com/

1993 Supercharged Lincoln Continental
1989 HMMWV
2000 Buick-Powered Mid-Engined Sports Car

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