12vac to 12vdc

  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. You could use a rectifier and a capacitor. You have to calculate the value of capacitor depending on your DC load.

  4. 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. 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. 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. Integral

    Integral 7,288
    Staff Emeritus
    Science Advisor
    Gold Member

    You will not get 12VDC from a 12VAC source. There is a voltage drop across the diodes.
  8. 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. Don't forget 12 VAC is RMS...

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