What is the polarity of a car cigarette lighter adapter?

  • There is a center pin, and two outside tabs. Which are positive and negative?

    Ground outside... in most cars.

    @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).

    @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.

    A voltmeter is a handy tool. Pick a decent one up for $5 from Amazon.

    @PaulR -- you ae absolutely correct. however, how many currently produced cars do you know that have pos ground? pretty much a thing of the past. I fully understood Sampo's answer

    @LaRocka: true, but the OP didn't specify "currently produced", or even that the car was of US origin. It might seem pedantic, but there are still old cars around with positive grounds. It's better to be explicit about these things than to make assumptions.

  • 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.

    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 :-)

    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.

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Content dated before 6/26/2020 9:53 AM