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Old 10th October 2004, 12:59 PM   #1
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Default Transformer Wiring... 5 wires on secondary?

I am wiring a transformer to supply about 15-0-15 for an audio amplifier. I need help as I am first time wiring a transformer.

Here is what I have.

My transformer is a single primary 115V and and it seems a dual secondary.

The secondary section has 5 wires. 2 red 1 black and 2 green.

Both red to black measure 15v
Red to Red measures 30v
Green to green measures 3.8v
Green to red is 0v
Green to black s 0v

I am trying to figure what wires are part of which of the secondary windings?

Is there a center tap or do I need to make a series connection and create a center tap?

Thanks in advance,

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Old 10th October 2004, 02:47 PM   #2
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Location: Noord-Holland

red - black- red

Is there a center tap
the black wire

The green wires are a different winding that you don't need.
Leave them unconnected, and if bare copper wire is showing be shure it's not touching anything, i.e. isolate.

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Old 10th October 2004, 02:54 PM   #3
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Thanks. I have been told that I can't leave a secondary wiring unconnected, but maybe that is on the primary side.

As you say, I can leave the 2nd secondary not connected and isolated.

Can you clarify this?

Just a thought, can I put the 2nd secondary circuit in series to the 15-0-15 to increase the voltage?

Thanks again,

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Old 10th October 2004, 06:48 PM   #4
Enzo is offline Enzo  United States
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Location: Lansing, Michigan
DOn't do that. The 15-0-15 winding once rectified will give you +/-20 more or less, and you can regulate that down to +/-15 with a couple 7815 or similar things. Ading the other winding in there creates many new questions. Just tape the green wires and anchor them out of the way somewhere. No reason in the world they HAVE to be in use.
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Old 10th October 2004, 07:58 PM   #5
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Thanks. Very helpful.

I will use just the 15-0-15 winding.

I purchased the transformer from a surplus store. I do not know the power rating. The center tapped winding is 30V. How do I measure the VA rating?
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Old 11th October 2004, 03:10 AM   #6
Enzo is offline Enzo  United States
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Location: Lansing, Michigan
If you look in a tranformer makers catalog you will see the dimensions of them listed by wattage or VA (volt-amps, close enough to wattage for me) The output current and voltage can vary, but the wattage determines the size of the iron. A tranny that puts out 12 volts at 10 amps would be the same size as one that puts out 24v at 5A. or for that matter 240v at half an amp. All of those put out 120 watts.

You can infer the basic wattage by lookin at the size of the iron and comparing it to other know products. Not exact, but close. Once you know the wattage, you can check the voltage and infer current.

You can also load the secondary and monitor it to see how much current it produces before sagging a lot.
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