Can I see a schematic for a 110 <-> 220 V power converter?

Question

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.

Answer 1

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.

^{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:

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:

^{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.

^{simulate this circuit}

Answer 2

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.