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Thread: Ac/dc?

  1. #1
    DIY Member Bassman's Avatar
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    Default Ac/dc?

    Does the transformer on a low voltage lighting system, such as a monorail, put out AC or DC. Inquiring minds want to know. Thanks.

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    Electrical Contractor/Instructor jwelectric's Avatar
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    The transformer will state the voltage, wattage and hertz

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    Licensed Electrical Contractor Speedy Petey's Avatar
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    Usually AC, but what Mike (jw) said is better.

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    DIY Senior Member BrianJohn's Avatar
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    A Standard transformer coil to coil (primary to secondary) no rectifier will only transformer AC voltage. With the addition of a rectifier it can produce DC.

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    DIY Member Bassman's Avatar
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    Thanks, I have a reasonable understanding of what transformers do, but I wanted to know whether to buy a DC or AC for the monorail light system. I'm purchasing online and the sites carry both. I'll be using two pin xenon lamps in the fixtures.

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    Electrical Contractor/Instructor jwelectric's Avatar
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    They should be able to advise you on which one you need when you make your order.

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    Plumber jimbo's Avatar
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    A transformer can only take and AC input, and output an AC voltage. A power supply, which would include a transformer and some type of rectifier ( half wave, full wave, bridge) and would output DC votage.

    Most light bulbs are rated for AC or DC, but not both, although with the proper circuit, you could possible use one either way. Basically, you should find out the voltage , number of volts, and AC or DC, for the bulbs you will use, then get the appropriate power.

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    Moderator & Master Plumber hj's Avatar
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    Default ac/dc

    Basically, for the same load DC requires larger wiring, (which is just one of the reasons the country does not run on DC), although for small loads the difference may be acedemic.

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    Engineer Furd's Avatar
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    Do you have a source for that, HJ? I've actually studied this a bit and while I can not find any specific source for D.C. ampacities it might be just the opposite of what you state because A.C. has a tendency to travel on the surface of the conductor. This is known as the "skin effect" and is why increasing the size of a conductor does not necessarily give a proportional increase in the ampacity.

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    In the Trades Bob NH's Avatar
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    The skin effect is negligible at 60 Hz. The resistance is substantially the same for AC and DC.

    One disadvantage of DC is that it is harder to extinguish the arc in switches because the voltage and current don't transition through zero. Therefore, most switching devices have lower ratings for DC than for AC.

    Also, many (most) dimmers will not work with DC.

  11. #11
    Homeowner geniescience's Avatar
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    Quote Originally Posted by Bassman
    ... I wanted to know whether to buy a DC or AC for the monorail light syste....
    availability of the bulbs,
    cost of the bulbs, and
    lifespan of the bulbs. - Some DC voltage systems are known to blow their bulbs a lot.

    Those are three factors that would make me order one system over another.

    Also, if I wanted to mix it with another type of bulb, I would have to stick with 110 V AC bulbs. No choice.


    The manufacturer will say what the output of their transformer is. It keeps AC input as AC, and DC input as DC.

    Another word for rectifier is inverter. A transformer combined with one of these is now a more complex device. Can be called a power supply. Cannot be called a transformer because it alters the type of output waveform, from AC to DC. or from DC to AC.


    David

  12. #12
    In the Trades Bob NH's Avatar
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    A DC to DC device is a converter; not a transformer.

    A transformer connected to AC is a short circuit, or very nearly so.

    A transformer requires the inductance together with the alternating nature of the current to provide enough impedance to prevent the circuit from darwing too much current.

  13. #13
    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by Bob NH
    A transformer connected to AC is a short circuit, or very nearly so.
    Didn't you mean to say DC instead of AC in the statement above?

  14. #14
    Homeowner geniescience's Avatar
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    DC bulbs' lifespan may be shortened by the DC power source ("supply") even though the bulbs themselves may have an official lifespan in the thousands of hours. I have heard of that happening.

    Someone else signed in here may know more and tell you more; I'd like to know too.

    Bassman, this is to stay on topic and tell you things that relate to your question.

    As for the guys wh want to discuss short circuits, impedance, inductance, converters and all that, I think I'll wait a bit and let Electrical Engineers add definitions and a little bit of direction. I am sure someone knows how to explain it all in a few words.

    Besides, Bassman, you deserve an answer to your first question. After that, if people want to keep on discussing other things closely related to your question, I won't speak up to disagree.


    David

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    In the Trades Bob NH's Avatar
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    Quote Originally Posted by jwelectric
    Didn't you mean to say DC instead of AC in the statement above?
    Yes, DC will make it approach a short circuit; not AC.

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