12Vac Help

Discussion in 'General Electronics Chat' started by ColonialBld, Jun 2, 2004.

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  1. ColonialBld

    Thread Starter New Member

    May 31, 2004
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    Have exterior lighting to lit up the outside landscaping of my house which I run off a exterior transformer rated at 12VAC, 60hz, 2.5 amps, 300 watts. I am running about 240 watts of coach lights over 3 lines off the above mentioned transformer as of right now. My problem is that I just built (2) small fountains for the outside landscaping which run off of low voltage pumps rated at 12VAC, 0.300 Amps, 2.5 watts and my transformer is to powerful. Without ripping up my landscaping because this is the only enjoyment my wife has because of terminal illness. Does anyone know how to step down the amperage of one line to supply these pumps? I believe that it can be done, I just don't have the techinical background to do it. Any help in this matter would be greatly appreciated. Thank you Bill
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    Hi,

    You don't have to worry. The fountain pumps won't pull more current than they need just because it's there. The power rating is inherent in the pump motor, and not dependant on the supply. Give them 12 VAC and they will draw 300 mills. Keep your transformer.
     
  3. Whatashame

    Member

    Nov 30, 2015
    83
    12
    Just for added information for the future projects. You need to always know voltage and wattage. Wire size and lenght of wire on 12volts AC circuits are most important. Most of those transformers are labeled very well. Watts is usually called "VA" on transformers. Volts times amps equals watts. VA or watts, means the same thing. So does HP (horse power), marked on motors. They all mean wattages. Why so many different words for same meaning, I just can't remember. These transformers are usually AC volts and not DC volts. If you use a DC tester you won't get any reading and you will think there is no power . The transformers will be labeled "primary" or "secondary". Power in(120v) is primary, and you guessed it, output to what your operating is the secondary. AC is weaker than DC power. It just doesn't have the same kick, so these lights need to have heavy wire feeding them, then you tap off them using the wire that comes on the lights and motors. Always use water proof (auto) fuse holders to protect your equipment.
     
  4. WBahn

    Moderator

    Mar 31, 2012
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    Your numbers don't make sense -- you say a transformer rated at 12 VAC, 60 Hz, 2.5 A and then say 300 W. But 2.5 A and 12 VAC is only 30 W. Are you SURE it is 12 VAC and not 120 VAC?

    If the voltage is a match, then you don't need to worry about the amperage as long as the transformer can handle at least the needed current. The actual draw will be whatever the load pulls.
     
  5. WBahn

    Moderator

    Mar 31, 2012
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    VA and W are NOT the same thing. VA is apparent power and is the simple product of RMS voltage and RMS current without regard for the phase relationship. W is real power and takes the power factor into account. You can have lots of VA and little, if any, W in a system. Transformers are sensitive to the apparent power, which is why they are rated in VA and not W.

    What do you mean by AC is weaker than DC? The wire size you need is dictated by the current. If you are stepping down the input voltage to a lower voltage then, to get the same power, you will need more current. It has nothing to do with whether it is AC or DC.
     
  6. WBahn

    Moderator

    Mar 31, 2012
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    MOD NOTE: And I just realized that you went out of your way to respond to a thread that is well over a decade old. What's the point? If you feel you need to revive this topic, then please start a new thread of your own and reference this one.
     
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