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How to wire this trafo for 110V?
How to wire this trafo for 110V?
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Old 29th March 2010, 08:10 PM   #1
maurycy is offline maurycy  United States
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Default How to wire this trafo for 110V?

I have dual secondaries trafo that I would like to use for my LM3875 gainclone. I am just not sure how to wire the four main leads for 110V. Here is the picture and specs are:

in: 110/220V 60/50Hz
wires: orange red brown black

out: 2 x 21.5V 2.7A
wires: blue black
wires: red white

Is there a simple way to measure what's what or maybe somebody have the same trafo in their project?

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Old 29th March 2010, 08:30 PM   #2
event horizon is offline event horizon  England
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In theory you need to parallel the two primaries & nothing else. The pic helped but i'm still not sure as there is no mention of primary phase.

From what i can gather you need to connect the Orange & Brown together & then the Red & Black together & you should have a 110V primary. One end IE Orange/Brown will become Live & the other end (Red/Black) will become Neutral. Well that's if they explained things without confusing people too much.

I'd check it out by feeding the thing with a function generator output at 50/60Hz before sticking mains into it first though, just to make sure the primaries are in phase If it's wrong you'll get no output voltage on the secondaries.
"Never let your morals prevent you from doing what is right!" Salvor Hardin
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Old 29th March 2010, 08:58 PM   #3
AndrewT is offline AndrewT  Scotland
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This is precisely the query I had many years ago, before I discovered that the bulb tester existed.

Use the bulb tester between the mains and your transformer.
Identify the two pairs, a pair has near zero resistance between the wire ends.
Couple one pair of primary wires to the plug top.
Power up.
The bulb might flash dimly or not at all.
Check the secondary AC voltage.
Switch off. Was the secondary voltage as expected?

Now add the second primary in parallel to the first at the plug top.
Power up.
The bulb will light up or will flash dimly and go out.
If it lights up, the primaries are out of phase. Swap the two wires of the second primary that you just added.
If the bulb goes out, check the secondary voltage.

You cannot blow the mains fuse doing this, you cannot damage the transformer doing this.

Try doing the wrong phasing of the Primary without a bulb tester is risking a serious fault and damage to equipment and yourself.
regards Andrew T.
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Old 29th March 2010, 09:07 PM   #4
maurycy is offline maurycy  United States
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Thanks. I have test bulb setup and ready (that's from my first gainclone project).
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Old 30th March 2010, 06:31 AM   #5
quadtech is offline quadtech  India
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I have the XFM-D0012 toroid too from Apex Jr and verified that the primary
windings are Orange-Red and Brown-Black.

Taking a guess at the phases, the likely connection seems to be -

110V Line - Orange+Brown
110V Neutral - Red+Black

The bulb tester is your friend here.

Note: I haven't hooked up this toroid, and I am not on 110V mains.

Last edited by quadtech; 30th March 2010 at 06:34 AM.
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