Transformer primary wiring help

This is not mine, but someone asked me how to use it. The primary side is usually printed "0-110V, 0-110V", but this transformer is different. From its label, it seems BLEGRN/YEWRED is for 110v input, and GRN/RED is for 220v input. If I input 110V through BLEGRN/YEWRED, what should I do with GRN/RED? Keep floating? How about 220v input? Should I connect BLEGRN/YEWRED?


transformer.jpg
 
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rayma

Member
2011-04-29 8:37 pm
it seems BLEGRN/YEWRED is for 110v input, and GRN/RED is for 220v input.
If I input 110V through BLEGRN/YEWRED, what should I do with GRN/RED?
Keep floating? How about 220v input? Should I connect BLEGRN/YEWRED?

It seems that there is a single primary with two taps for the 110V. Use your dvm to confirm this
with the ohms function. If so, then you would leave the 220V connections floating when using
a 110V input, and carefully insulate them. Similar for a 220V input.
 
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I'm trying to read the label.
I think it shows:
GRN BLEGRN YEWRED RED
that means one wire is blue, one wire is blue&green, one wire is yellow&red, one wire is red.
i.e. 4wires indicating a dual primary.
Please confirm that the primary has 4 wires or 3 wires and confirm if it has two isolated primaries or one primary with multiple taps.

Before you connect anything you MUST know what the primary is !!!!!!!
 
Wire the two primaries in series. Leave the secondary open circuit, but protected from accidental touching.
Insert a Mains Bulb Tester between the mains and the transformer.
Use a low power tungsten filament bulb, (try 40W).

Power ON.
If the bulb is bright, then the phase of the primaries is wrong.
Power OFF.
Change ONE winding by swapping the two tappings.
PowerON.
If the bulb appears to be off, then check the secondary voltage. It will be a little high due to no load, or nearly nothing.
 
Wire the two primaries in series. Leave the secondary open circuit, but protected from accidental touching.
Insert a Mains Bulb Tester between the mains and the transformer.
Use a low power tungsten filament bulb, (try 40W).

Power ON.
If the bulb is bright, then the phase of the primaries is wrong.
Power OFF.
Change ONE winding by swapping the two tappings.
PowerON.
If the bulb appears to be off, then check the secondary voltage. It will be a little high due to no load, or nearly nothing.


Hi AndrewT,

Thanks for the instructions. Let me guess. If the one of the primaries is not in phase with the other, there will be power consumption. (And no secondary output due to cancellation of the primaries) Is it correct?

Poting
 
Yes, the inductance of the two primaries is out of phase (it becomes esentially zero) and the remaining impedance to mains voltage is the primary resistance.
The transformer primaries when out of phase would raw an enormous current and burn out very quickly.

It was this concern that made me ask here for a solution many years ago and NO Member came back with any help. A while later I stumbled upon the Mains Bulb Tester and realised that it was the safe solution to the primary phasing problem.

I have recommended it to Members many times since then. And realised just how good a tool it is for diagnosing other faults.
 
a correctly wired dual primary with the output load drawing very little current may not even blink when using a low power bulb.

The short term starting pulse can be so low that the bulb filament does not even glow dimmly because it does not get hot enough.
The cold filament resistance is ~8% to 10% of the hot filament resistance. It disspiates very little power while it is still cold.
 
Just want to post some info for this transformer in case someone got the same problem.

Printed label:
GRN 220V-BLU 110V-YEW 110V-RED 220V

Actual primary winding:
110V RED~0V BLU , 110V YEW~0V GRN

For 220V input:
1.Connect BLU & YEW, (RED,GRN) is AC input
or
2.Connect GRN & RED, (YEW,BLU) is AC input

For 110V input:
1.Connect BLU & GRN, RED & YEW.
 
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