There is a center pin, and two outside tabs. Which are positive and negative?
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asked Oct 23, 2012 at 7:17
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\$\begingroup\$ Ground outside... in most cars. \$\endgroup\$– Sampo SarralaOct 23, 2012 at 7:45
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\$\begingroup\$ Seems like this information is also in en.wikipedia.org/wiki/DC_connector. \$\endgroup\$– Sampo SarralaOct 23, 2012 at 7:47
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1\$\begingroup\$ @Sampo: "ground" doesn't tell you anything about polarity, e.g. there are cars where the battery +ve terminal is connected to the chassis (i.e. positive ground). \$\endgroup\$– Paul ROct 23, 2012 at 7:59
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1\$\begingroup\$ @PaulR sorry about that, my mistake. I meant negative by ground. In cigarette connector negative should (probably there are exceptions too) always be outside no matter how grounding is done. \$\endgroup\$– Sampo SarralaOct 23, 2012 at 8:02
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2\$\begingroup\$ A voltmeter is a handy tool. Pick a decent one up for $5 from Amazon. \$\endgroup\$– Kris BahnsenOct 23, 2012 at 20:49
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1 Answer
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Every car that I have seen had center-positive cigarette lighter 'sockets'.
All (as far as I know) modern cars use negative ground systems, so the outer negative 'body' is vehicle ground and positive center is battery
You would expect this polarity to be maintained even with positive ground vehicles made by any sane manufacturer (and most insane ones as well).
AFAIR some old British Vehicles and Volkswagens had positive ground systems. No doubt there were others.
answered Oct 23, 2012 at 8:23
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5\$\begingroup\$ Ditto for me. Every car I've seen had positive on center pin. But I always put a protection diode in all devices that I made that needs to be powered from those sockets. Better safe than sorry :-) \$\endgroup\$– AxemanOct 23, 2012 at 8:39
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2\$\begingroup\$ To @Axeman's point, if you can afford the voltage drop just put in a bridge rectifier -- that way it doesn't matter which input wire is which, you'll get +V where you expect and GND where you expect. \$\endgroup\$– Doktor JDec 24, 2014 at 17:58