2
\$\begingroup\$

I would like to see a schematic for those 110 <-> 220 V power conversion transformers-in-a-box. I've read they are autotransformers (one winding with multiple taps). I'm using one to step up 110 to 220 V and would like to see if there's any way to get split-phase 220 V out of it.

I've looked at industrial isolation transformers with this capability and they are VERY expensive.

Clarification to re-open: Can a 110 V to 220 V auto transformer be used to get a 220 V split-phase output? Must an isolation transformer be used? Please give reasons.

\$\endgroup\$
9
  • \$\begingroup\$ You could take one apart and see how it works. (Be careful of capacitors that may retain a charge) \$\endgroup\$
    – user253751
    Jan 13, 2023 at 15:50
  • 1
    \$\begingroup\$ Thanks, but no capacitors: just a big honking toroidal transformer/autoformer (mine is rated for 5 KW). \$\endgroup\$
    – Rob Lewis
    Jan 13, 2023 at 16:05
  • 2
    \$\begingroup\$ well there's your answer: your one is a big honking transformer. Some very cheap ones try to fake it, poorly, with a triac. Like a light dimmer set to 50%. \$\endgroup\$
    – user253751
    Jan 13, 2023 at 16:06
  • \$\begingroup\$ how is the VERY expensive relevant to the question? \$\endgroup\$
    – jsotola
    Jan 13, 2023 at 17:03
  • \$\begingroup\$ How much schematic do you expect for a transformer? There's one component - a transformer. An auto-transformer doesn't even have separate primary and secondary windings. \$\endgroup\$
    – Simon B
    Jan 13, 2023 at 22:59

2 Answers 2

3
\$\begingroup\$

All the circuits below need input and output fusing. This is not shown, but absolutely necessary for fire safety.

A 110->220V autotransformer of course provides a split phase output, but the output is not always ground-referenced, and thus you can't use it unless you're careful. In a split-phase supply, the center tap is neutral and bonded to ground. You can get that in an auto-transformer, as long as the central tap is connected to Neutral.

schematic

simulate this circuit – Schematic created using CircuitLab

In the schematic above, disregard the dummy primary winding of the transformer - CircuitLab doesn't have an auto-transformer symbol.

As long as the central tap is connected to neutral, LIVE2 is 180 degrees out of phase with LIVE, and thus you have a split-phase supply:

LIVE and LIVE2 waveforms

I've looked at industrial isolation transformers with this capability and they are VERY expensive.

Not really. For a fully isolated split-phase supply, you need is two standard 120V-120V isolation transformers, connected as follows:

schematic

simulate this circuit

If all you want is to add a split phase to an existing supply, just one 1:1 isolation transformer does it. It has the same amount of wire as an autotransformer, and should cost about the same.

schematic

simulate this circuit

\$\endgroup\$
0
\$\begingroup\$

Can a 110 V to 220 V auto transformer be used to get a 220 V split-phase output? Must an isolation transformer be used? Please give reasons.

Yes. As long as you don't need isolation, you can use a 110 to 220 VAC autotransformer to generate split phase power from a single phase 110 VAC source.

There are details about grounding and bonding and so forth that you need to take care of.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.