Hello Guys. I need help identifying which pair of leads can be used for 110V. I tried continuity test with multimeter and got continuity on the following pairs (1&3) and (2&4).

• The label on the transformer shows the appropriate connections. North American AC power is nominally 120 volts, but is often called 110 volts or 115 volts. Commented Mar 15, 2017 at 17:51
• " I tried continuity test with multimeter and got..." that's right. The transformer primary will be two separate windings, one from pins 1-3 and the other from pins 2-4. With that information, you can draw a circuit diagram and see how linking the pins connects the two windings in series for 230V, and in parallel for 115V. Commented Mar 15, 2017 at 21:14

It's not as obvious as it might be, but the label tells you to put line voltage onto pins 1 and 4 whatever voltage you want to run from.

Then for use on 230V, you link pins 2 and 3 together, putting the windings in series without cancelling each other out.

Or for use on 115V, you link pins 1 and 2 together, and pins 3 and 4 together. That way means the 115V windings act in parallel, again without cancelling each other out.

Edit: This arrangement allows the use of a DPDT switch as a line voltage selector in a way that makes it safe to change while powered up, and there are plenty on the market suitably labelled (usually slide switches). Here's how you'd connect it up, it has a rather pleasing symmetry...

• good catch, not at all obvious, I would have probably blown that one up! Commented Mar 15, 2017 at 19:12
• @Finbarr. Thanks mate. I have both 110V and 220V output in my house but I'll be using only 110V for safety. I did like you said, linked 1&2 and 3&4 together. Then I connected my 9V AC transformer to the input i.e 1 and 4 pins. Checked the voltage with my multimeter at input its 8.8V and the output was 1.6~1.7V(Vin/Vout=5.17). and with 2&3 pin(220v setup) output was 0.7V. So, I guess I can safely connect to power outlet now.
– RSB
Commented Mar 15, 2017 at 19:34
• @RahulSalin For safety I'd rather use 220V, because fot the very same power output you draw half the current needed for 110V supply. Commented Mar 16, 2017 at 11:07
• @RahulSalin if this answer helped you solve your problem, you should accept it using the green check under the up/down vote icon Commented Mar 16, 2017 at 14:04
• @Aaron Thanks for mentioning it. I wasn't aware of that feature.
– RSB
Commented Mar 16, 2017 at 14:51

I thought I'd provide a picture to illustrate Finbarr's description, as I think that may help:

Just to make things explicit.