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Old 23rd September 2002, 08:42 AM   #1
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Default How to use this transformer?

Hi all,

I've got a toroidal transformer that I'd like to find out how to use. This tranny's got four pairs of wires on the secondary side. The spec says that each pair gives 42VAC/4.64A (for a total 780VA). I want to use this for a 2 channel amp, so if two pairs of outlets could be combined for +/- 60VDC it would be great.

In a perfect world I would just connect two wires and use this as ground. Unfortunately this doesn't seem to work. When I messure the output voltages I get 42VAC over each pair of wires, but when I check voltages accross the pairs I get something like 40V and 2V (not 42V and 0V).

Does anyone have any suggestions on how this transformer might be wired, or how to use it for +/- 60V supply rails?

-truls
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Old 23rd September 2002, 08:55 AM   #2
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If the transformer has the standard colours:

Yellow = 230 V in

Sec 1 = brown-blue
Sec 2 = green-red

Connecting with "center tap"
brown and red to ground
blue and green to the rectifier bridge
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Old 23rd September 2002, 09:27 AM   #3
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HI,

First try to swap the connected wires i.e if wire 2 of secondary 1 is connected to wire 2 of secondary 2 then connect wire 2 of secondary 1 to wire 1 of secondary 2 and measure again. If the secondaries are separate (i.e. not connected physically which you can verfy by using a resistance meter) it should work.

The 42 VAC will however maybe not give 60 VDC as 42*1.414 = 59.4 without taking into account the losses in the bridge.

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Old 23rd September 2002, 12:26 PM   #4
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Default It works!

I tried to do what peranders says before. I don't know why it didn't work then, maybe I had a bad wire or something.

Next question; the secondaries measure 42VAC without load, can I count this as 59V in the circuit, or will the voltage of the tranny fall under load?

-truls
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Old 23rd September 2002, 12:54 PM   #5
UrSv is offline UrSv  Sweden
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The voltage will drop when loaded and the rectifier will also have a drop.

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Old 23rd September 2002, 01:04 PM   #6
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If this is for a Class A amp, we generally count on between VAC*1.2 and VAC*1.25.... for Class AB etc, VAC*1.3 is probably more realistic.
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