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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).

Thanks in advance. Cheers

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    \$\begingroup\$ 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. \$\endgroup\$ Commented Mar 15, 2017 at 17:51
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    \$\begingroup\$ " 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. \$\endgroup\$
    – alephzero
    Commented Mar 15, 2017 at 21:14

2 Answers 2


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...

enter image description here

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    \$\begingroup\$ good catch, not at all obvious, I would have probably blown that one up! \$\endgroup\$
    – Neil_UK
    Commented Mar 15, 2017 at 19:12
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    \$\begingroup\$ @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. \$\endgroup\$
    – RSB
    Commented Mar 15, 2017 at 19:34
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    \$\begingroup\$ @RahulSalin For safety I'd rather use 220V, because fot the very same power output you draw half the current needed for 110V supply. \$\endgroup\$
    – Crowley
    Commented Mar 16, 2017 at 11:07
  • \$\begingroup\$ @RahulSalin if this answer helped you solve your problem, you should accept it using the green check under the up/down vote icon \$\endgroup\$
    – Aaron
    Commented Mar 16, 2017 at 14:04
  • \$\begingroup\$ @Aaron Thanks for mentioning it. I wasn't aware of that feature. \$\endgroup\$
    – 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:

enter image description here

Just to make things explicit.


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