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12vac to 12vdc

by TechMiller
Tags: 12vac, 12vdc
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TechMiller
#1
Aug21-11, 09:11 AM
P: 10
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

Thanks!
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Mbert
#2
Aug21-11, 09:33 AM
P: 64
You could use a rectifier and a capacitor. You have to calculate the value of capacitor depending on your DC load.

M.
skeptic2
#3
Aug21-11, 12:53 PM
P: 1,803
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.

TechMiller
#4
Aug21-11, 03:22 PM
P: 10
12vac to 12vdc

Quote Quote by skeptic2 View Post

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...#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!
skeptic2
#5
Aug21-11, 10:14 PM
P: 1,803
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.
Integral
#6
Aug22-11, 10:23 PM
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Integral's Avatar
P: 7,314
You will not get 12VDC from a 12VAC source. There is a voltage drop across the diodes.
TechMiller
#7
Aug23-11, 06:15 AM
P: 10
Quote Quote by Integral View Post
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.
Mbert
#8
Aug23-11, 07:06 AM
P: 64
Don't forget 12 VAC is RMS...

M.


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