Converting 12VAC to 12VDC to Power PC Fans

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To convert 12VAC to 12VDC for powering two small PC fans, a full wave rectifier and a capacitor are essential components. The voltage across the capacitor will be approximately 16V due to diode drops, necessitating a voltage regulator to reduce it to 12V. If the transformer is center-tapped, rectifiers should be placed at the outer connections, while a single full wave rectifier is suitable for non-center-tapped transformers. Concerns about wattage are minimal since the power supply exceeds the fans' requirements, and additional resistors may not be needed. Ultimately, achieving a stable 12VDC output will depend on the specific setup and testing of the components.
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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 http://www.ebay.com/itm/ELECTRONIC-TRANSFORMER-120VAC-12VAC-75W-MAX-/270458210358?_trksid=p5197.m7&_trkparms=algo%3DLVI%26itu%3DUCI%26otn%3D5%26po%3DLVI%26ps%3D63%26clkid%3D2218825548378729626#ht_609wt_1396"

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

M.
 
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.
 
skeptic2 said:
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.
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/270458210358?ssPageName=STRK:MEWNX: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.

Thanks!
 
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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.
 
You will not get 12VDC from a 12VAC source. There is a voltage drop across the diodes.
 
Integral said:
You will not get 12VDC from a 12VAC source. There is a voltage drop across the diodes.

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.
 
Don't forget 12 VAC is RMS...

M.
 

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