Transformer Wiring Confusion

Tom D · 16th September 2002, 03:40 PM

I would like to know exactly what "Center Tapped" means with a Transformer?

Example: If you needed to replace a Power Transformer that has only 2 primary wires and only 2 secondary wires; Could you replace it with a "center tapped" model?

Would the "middle, third or center wire be left open in this case? or is it used as a ground? Thanks for any help.

hitsware · 16th September 2002, 03:47 PM

the center tap would be left open

audioPT · 16th September 2002, 03:59 PM

Center tap being left!!

Be sure that the voltage of the center tapped transformer is half of the original

Like this:

Original is 24V
Center Tap must be 12V-0-12V

If not, you will get 48V (24V-0-24V)

Is this ok?

Pedro Martins

Tom D · 16th September 2002, 04:35 PM

Thanks for the quick replies.

The transformer in question has 2 primary wires and 2 secondary wires. The input would be 120 VAC. The secondary output measures 24 or 25 VAC across the 2 secondary wires. This is a Power Supply circuit that puts out 24 VDC(Regulated) at 500ma.

My confusion seems to be: What rating of transformer would I look for as a replacement? Example: 24 or 25 VAC center-tapped or 12VAC center-tapped? Also; what amp rating would I need; 500ma or possibly 1A or 2 A?

audioPT · 16th September 2002, 04:54 PM

Well, I think I can explain.

If the original transformer is 24VAC, then any substitution must be 24VAC (without center tap) or 12VAC with center tap. In this last case, use the external wires (leave the center tap).
This way you get 24VAC.
About the Amp rating, if the PSU is going to be 500mA, then the transformer must be, at least 1A.
Why? because in the circuit there are components that absorve energy and the diodes and/or other semi-conductors have some losses.
There are other factors that I don't explain because of the complexity.
Some people use the formula I(transf) = I(out)*1,414.

Did I helped?

Regards

Pedro Martins

Tom D · 16th September 2002, 08:13 PM

audioPT,

Wow!! Thanks so much. You could not have explained it better! I really appreciate your help. Thanks again.

Tom

skaara · 16th September 2002, 10:32 PM

Center tapped transformers are commonly used in audio amps... 24V CT (center tapped) transformer has 12V-0V-12V on secondary.. see pic..

16th September 2002, 03:40 PM	#1
Tom D diyAudio Member Join Date: Sep 2002 Location: USA	Transformer Wiring Confusion I would like to know exactly what "Center Tapped" means with a Transformer? Example: If you needed to replace a Power Transformer that has only 2 primary wires and only 2 secondary wires; Could you replace it with a "center tapped" model? Would the "middle, third or center wire be left open in this case? or is it used as a ground? Thanks for any help.

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16th September 2002, 03:47 PM	#2
hitsware diyAudio Member Join Date: Mar 2002	the center tap would be left open

16th September 2002, 03:59 PM	#3
audioPT diyAudio Member Join Date: Aug 2002 Location: Right here	Center tap being left!! Be sure that the voltage of the center tapped transformer is half of the original Like this: Original is 24V Center Tap must be 12V-0-12V If not, you will get 48V (24V-0-24V) Is this ok? Pedro Martins

16th September 2002, 04:35 PM	#4
Tom D diyAudio Member Join Date: Sep 2002 Location: USA	Thanks for the quick replies. The transformer in question has 2 primary wires and 2 secondary wires. The input would be 120 VAC. The secondary output measures 24 or 25 VAC across the 2 secondary wires. This is a Power Supply circuit that puts out 24 VDC(Regulated) at 500ma. My confusion seems to be: What rating of transformer would I look for as a replacement? Example: 24 or 25 VAC center-tapped or 12VAC center-tapped? Also; what amp rating would I need; 500ma or possibly 1A or 2 A?

16th September 2002, 04:54 PM	#5
audioPT diyAudio Member Join Date: Aug 2002 Location: Right here	Well, I think I can explain. If the original transformer is 24VAC, then any substitution must be 24VAC (without center tap) or 12VAC with center tap. In this last case, use the external wires (leave the center tap). This way you get 24VAC. About the Amp rating, if the PSU is going to be 500mA, then the transformer must be, at least 1A. Why? because in the circuit there are components that absorve energy and the diodes and/or other semi-conductors have some losses. There are other factors that I don't explain because of the complexity. Some people use the formula I(transf) = I(out)*1,414. Did I helped? Regards Pedro Martins

16th September 2002, 08:13 PM	#6
Tom D diyAudio Member Join Date: Sep 2002 Location: USA	audioPT, Wow!! Thanks so much. You could not have explained it better! I really appreciate your help. Thanks again. Tom

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