13.2 volts can become 18 volts, true.  Can also become 24+ volts when some idiot jumps with two batteries, -13.2 volts when some idiot hooks up the jumping battery reversed, or 60 volts when an inductive load dumps it's cookies.  




-- Lawrence Lile, P.E.
Electrical and Electronic Solutions
Project Solutions Companies
www.projsolco.com
> -----Original Message-----
> From: Howard Winter [mailto:HDRW@H2Org.demon.co.uk]
> Sent: Friday, September 17, 2004 6:57 AM
> To: Microcontroller discussion list - Public.
> Subject: Re: [PIC:] [PIC]: General PIC Design Guidelines
> 
> Kev,
> 
> On Fri, 17 Sep 2004 11:25:43 +0100, Kev Pearce \(kevp.com\) wrote:
> 
> > So with the 7805 if the input were nearer the output it would disapate
> less
> > power (makes perfect sense really!!) but not too near as you to achieve
> as
> > stable a 5V as possible. I'll add a larger heatsink I think, one of the
> > laying down ones rather than the standing up types - just like my dev
> board
> > has! I guess I could drive any larger outputs from the 12V input rather
> than
> > the 5V but in an automotive I don't want to use the supply voltage
> without
> > some form of regulator.
> 
> Just remember that "12V" in a car is nothing of the sort!  13.2V is the
> "norm" while running, but can drop to
> 8V while the starter is turning over, and can reach 18V if there's serious
> battery charging going on.  Make
> sure your regulator can handle the latter, and/or that your circuit can
> cope with being a brief voltage drop
> if the regulator drops out during starting.  Also make sure you noise-
> filter every cable that connects to your
> device - the Automotive environment is very electronics-unfriendly!
> 
> Cheers,
> 
> 
> Howard Winter
> St.Albans, England
> 
> 
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