On 10/22/2010 2:39 PM, Adam Field wrote:
> I have a hobby project I've been developing that I want to turn into a
> self assembly kit, eventually. So far google hasn't answered all my
> questions about the hostility of an automobile environment. How stable
> is the voltage coming off the alternator? How bad are the transients?
> Are older cars worse? I assume you would see anywhere from 12-15VDC
> normally depending on engine speed / alternator load, say nothing of
> transients. If I was using a voltage regulator with a max 35VDC input,
> is it safe to assume I would rarely see a condition to damage the
> regulator? If not, what sort of input filtering should I use? Would a
> "pi" http://en.wikipedia.org/wiki/Capacitor-input_filter  filter be a
> good idea? Or simply a 16-30V zener diode may be enough?
>
> My other question is temperature extremes. If I stuck with the
> Microchip Industrial range, -40C to 85C, I would also assume I would
> not worry about the lower limit, as cars probably have trouble
> starting below -40C. The upper limit (85C, 185F) though may be
> approached during summer, in the interior, in full sun (on dashboard)
> and probably with a black plastic case to make the situation worse.
> Does anyone know what to expect?

Littelfuse has a good pdf on the topic.  Notice the 120V transients.

It's AN9312; google knows:

http://www.google.com/url?sa=3Dt&source=3Dweb&cd=3D11&ved=3D0CBIQFjAAOAo&ur=
l=3Dhttp%3A%2F%2Fwww.littelfuse.com%2Fdata%2Fen%2FApplication_Notes%2Fan931=
2.pdf&rct=3Dj&q=3Dautomobile%20power%20%22load%20dump%22&ei=3D0wzCTMj_NIj6s=
wOfwuikCw&usg=3DAFQjCNEq2d46raWonvVqbzrzy8f_XgqVYw&sig2=3DgTFAsKpn2iA3YyjpK=
Jfy2Q&cad=3Drja
--=20
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