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  1. #1
    500+ This must be a daytime job



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    Does polarity matter when wiring a DC incandescent bulb?

    I have recently acquired a c182 glareshield that perfectly matches up to my MIP. Can't tell you how much this little addition adds to my project.
    This is only a dry fit, as I am not going to permanently affix it until I have some paint and some more finish slapped on this thing

    Anyway, it comes with lighting installed to illuminate the MIP. It has 5 sockets mounted underneath it, with 5 little bulbs behind 4 little red, and 1 little blue lens. Each socket has 2 wires coming out, that are not marked to differentiate positive or ground.

    Will I fry these things if I hook them up bass-ackwards? Heaven knows how much a little light bulb for a 71 c182 might cost, and I don't really want to take a chance.

    Question 2: Anyone know what the VDC in the 182 electrical system is? I suspect it is 24. It should not hurt the bulbs to run 12 through them should it? I was thinking it would just make them more dim.

    Question 3: If 12V is ok, would there be a problem running them off an old PC power supply?

    Thanks in advance for your tutelage!
    http://juneaucessnasim.blogspot.com
    N58243 (virtual)- Low and Slow...

  2. #2
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    Re: Does polarity matter when wiring a DC incandescent bulb?

    Most real aviation bulbs I've come across are usually 28vdc. I've hooked them up to a PC PSU @ 12vdc and it will be really too dim, not even worth hooking up that way. You should be able to remove one of the bulbs and go down to your local auto parts store and match it up with a 12vdc bulb. I've done this several times and it works great. Even hooked up to a dimmer control and still works fine. Hope this helps.

    Cheers

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  4. #3
    500+ This must be a daytime job



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    Re: Does polarity matter when wiring a DC incandescent bulb?

    Great info thanks!
    Any thoughts on the polarity?
    http://juneaucessnasim.blogspot.com
    N58243 (virtual)- Low and Slow...

  5. #4
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    Re: Does polarity matter when wiring a DC incandescent bulb?

    Polarity is not an issue with incandescent lamps.

    However, in indicator assemblies there are sometimes diodes that result in a polarity requirement for the assembly. The diodes allow multiple circuits to activate a lamp without the different circuits interacting. For example, a landing gear indicator has one circuit for the gear up and another for lamp test.

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  7. #5
    500+ This must be a daytime job



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    Re: Does polarity matter when wiring a DC incandescent bulb?

    Success!

    I changed out the bulbs with 12 volt ones from the local auto parts shop. Cost me about $7.00.

    Had an old pc power supply lying around that died on the -5v rail so had to be replaced in my wife's machine. Grounded the green wire , spliced together a molex cable to plug into it, and Eureka!



    Have not decided if these are bright enough, but the great news is that there is another bulb that also fits that is brighter. I am thinking about buying a rheostat for a dimmer switch too!

    Sure feels good when some of my plans and dreams for this thing take shape. Thanks to all of you who contribute knowledge and projects around here to inspire and help out us noobs. Not everyone in this hobby is as forthcoming, patient and helpful as this forum. I am deeply grateful!

    Reid
    http://juneaucessnasim.blogspot.com
    N58243 (virtual)- Low and Slow...

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