# Connecting 230V to a Double 115V Transformer

• posted

I have a chassis mount transformer, 50VA 12V output, the input has four terminals, left to right:

0 - 115V 0 - 115V

How do I connect 230V to this, do I connect neutral to the 0 on the left, link first 115V to second 0, and live to the second 115V?

• posted

Don't connect the neutral to the transformer. If you do it will try to act as an autotransformer to balance any voltage imbalances, and at 50VA it will fail.

Connect one hot to the "0" of one winding, the "115V" of that winding to the "0" of the other winding, and the "115V" of the second winding to the second hot. This makes the windings add up to 230V.

You have to get the winding order correct, since if you get one of the windings backwards the transformer will fail in a puff of smoke.

Is there a wiring diagram on it? Most likely the center two terminals should be connected to each other and the two hots to the two outer terminals.

• posted

I have to admit I'm curious as to what the resulting output of the transformer would be if the two 115V coils were wired in parallel to 115 volts.

• posted

If both primary windings had exactly the same number of turns there should be no problem. Because of some magnetic circuit asymmetry, there may be a slight circulating current. This presumes correct wiring.

• posted

To be on the safe aide do the following.

1. Do not connect anything to the 12V winding. (Open circuit)
2. Connect 2 to 3. (Center two connections.
3. Connect 1 and 2 to no more than 120VAC.
4. Measure voltage from 1 to 4.
5. If the voltage between 1 and 4 is not double that from 1 to 2, go to step 9.
6. Remove all test wiring and equipment.
7. Make a permanent connection between 2 and 3.
8. Use 1 and 4 for your primary connection.
9. If the voltage between 1 and 4 is not close to zero, you are in over your head. STOP!
10. If the voltage is zero, then connect 4 to 2 and leave 3 open. You still may be over your head. That is, reverse how one primary winding is connected.
11. Use 1 and 4 for your primary connection.

If you cannot understand these instructions, get help.

• posted

This is a 50 VA transformer, which I doubt if would be connected to 230 V if US style mains supply. More likely to be European style 230 V single phase supply, with 230 V between phase (line, hot) and neutral, in which case the neutral does need to be connected to one end of the two primary windings, which need to be connected in series with each other.

The OP really needs to specific as to exactly what type of supply, or what country, is involved. It's not safe to assume anything if this is not specified.

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