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Thread: AC or DC

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    Default AC or DC

    I have a rather expensive Christmas decoration that has stopped working. It is a Father Christmas that has movement and a small light globe.

    The power supply has failed. It is 24 volts, but it does not state whether AC or DC

    How can I find out whether AC or DC.

    I have a 24 volt power pack in both DC and AC. If I plug the wrong one in will this do any damage?

    If it is DC how will I know the polarity.

    The DC supply that I have shows positive as the outer ring on the plug.

    I always thought that positive was the center pin.



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    Thread moved to correct section.

    It's most likely DC.

    Try opening the failed power supply and see if there are any rectification components inside... eg: diodes, rectifier, caps, etc and if there are, check continuity with a multimeter to the output connector to see which pin the positive wire is connected to.

    If there are no rectifying components eg: transformer only, then it will be AC and polarity can be either way around.

    Yes, most power connectors are positive to the centre, but there are some that are opposite, so it's very important if it's DC to ensure the polarity is correct for your device.

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    Next to the Voltage it should show what looks like an equals sign. (=)
    If both are dotted, it is AC.
    If one is solid and the other is dotted, it is DC.

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    I have an optical Christmas tree, this has a motor that drives a color wheel that when it rotates it changes the light color. This tree runs on 12V AC. (Original supply failed, so i now use an old halogen down-light iron core transformer)
    If you put DC in to an AC device it should just not work, and not cause any issues to the device. If it was a DC device and you put in AC, you are very likely to let the smoke out.

    As stated earlier, if you look inside the old power supply, you will see the components that make it a DC supply.
    Last edited by redgu; 02-01-19 at 11:05 PM.

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    If it is plugpack supply.Looking inside is a destructive exercise. Just easer to read what is on the plugpack.
    First plan of attack is always to check whether the power supply is actually faulty. Multimeter ?

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