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12vac to 12vdc

  1. Aug 21, 2011 #1
    Hey all, I am putting together a little LED project and have all of the LED figured out with 12vac drivers and all.

    What I am wanting to do is take a line from my 12vac and convert it to 12vdc to drive 2 small PC fans. (2x60mm) 2x 0.24w

    Anyone able to tell me the components I need to do this? Rectifier and or something else?

    If there is a certain size or wattage needed.

    The 120vac to 12vac transformer is one I got on ebay

    Last edited: Aug 21, 2011
  2. jcsd
  3. Aug 21, 2011 #2
    You could use a rectifier and a capacitor. You have to calculate the value of capacitor depending on your DC load.

  4. Aug 21, 2011 #3
    Is your transformer center tapped?

    If so, do you have 12 V from end to end or 12 V from center to end? If it is 12 V from center to end, you would put rectifiers in each of the outer connections and a capacitor from the junction of the capacitors to the center tap. The voltage across the capacitor should be 1 diode drop below Vpk or about 16 V. Normally a 12 V regulator would be used to reduce that voltage to 12 V.

    If your transformer has no center tap or if your center taped transformer has 12 V from end to end, then you would use a full wave rectifier and a capacitor connected from the positive side of the rectifier to the negative side. You will have about 16 V across the capacitor and you will still need a 12 V regulator to bring down the voltage to 12 V.
  5. Aug 21, 2011 #4

    I believe it is this one, though I do not have it in hand yet.
    This is a link to it. 12vac http://www.ebay.com/itm/27045821035...NX:IT&_trksid=p3984.m1439.l2649#ht_609wt_1396

    I did however today run to radio shack after doing some more research and put together a full wave rectifier, with a cap behind it, followed by a VR and another cap.

    The power input is 75w 12vac, I have 2 fans that are 12vdc, 0.24w each do I need to worry about wattage with the fans?

    Do I need to drop a resistor in after the VR?

    *Edit *
    Ok, so I was looking around and finally found the answer to this question.
    I don't need to worry about the current of the supply being more than that of the fans.

    Last edited: Aug 21, 2011
  6. Aug 21, 2011 #5
    If you are only going to use it to run the fans, you probably don't need the capacitor or the voltage regulator. You would want to use a full wave rectifier.
  7. Aug 22, 2011 #6


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    You will not get 12VDC from a 12VAC source. There is a voltage drop across the diodes.
  8. Aug 23, 2011 #7
    Yes, if it is a 12vac regulated supply.
    But until I have it to test I won't be sure, and if I have a few volts under the fans will just run a little slower and quieter.
  9. Aug 23, 2011 #8
    Don't forget 12 VAC is RMS...

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