Hi Ed and the group,
In addition to the 12/14 Volt question there are a few other points to
consider.
1) pretty big fast transients from loads like the starter motor
2) load dump conditions (battery becomes disconnected when engine is running)
where the alternator drives the voltage way above the normal ~14 Volts for a
time. This is more common that you might think, these days caused by lead-free
battery clamps failing. (Lead free battery clamps strikes me as a very bad
idea and does not accomplish anything compared to the battery itself and the
real source of lead from cars, the wheel weights flinging off wheels.) I have
observed first hand one of these clamps failing during use and immediately
replaced both clamps with nice lead ones.
Automotive electronics are designed to withstand load dump conditions but your
electronics may not be.
Doug
Price, Edward wrote:
________________________________
From: [email protected] [mailto:[email protected]] On Behalf Of
[email protected]
Sent: Monday, January 19, 2009 6:37 AM
To: Scott Xe
Cc: [email protected]
Subject: Re: Cigarette socket in vehicles
Hello Scott,
In the case of 12V accessories to plug in normally they have a
regulator
installed to prevent the overvoltage.
Thank you.
Rob Kado
EMC Engineer - Module Laboratory Operations
Chrysler
Initial assumptions can be deceiving. I recently bought a Magellan GPS.
It
operates on 5 VDC, and came equipped with an external "cigarette socket"
adapter. I assumed the cheapest, that there was a little resistor inside the
adapter, or just possibly a cheap linear regulator. On taking the adapter
apart (yes, I tend to do things like that), I was quite surprised to find a
little 2 custom IC switching converter, with input inductors, filter
capacitors and a hefty input overvoltage clamp.
The input voltage range was not specified, but it seems likely to be
capable
of 24 VDC operation.
Ed Price
[email protected] <blocked::mailto:[email protected]> WB6WSN
NARTE Certified EMC Engineer
Electromagnetic Compatibility Lab
Cubic Defense Applications
San Diego, CA USA
858-505-2780
Military & Avionics EMC Is Our Specialty
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