kevinkr said:
For 240V operation connecting two windings in series out of phase will get you lots of smoke! (Particularly if you don't use a fuse of suitable rating.)
On the primary side with two 120V pri's in series, it would. Out of phase series secondaries simply cancel and give very little voltage. Of course, it is NBD to connect a light bulb in series with anything when giving it the first power on test. On a couple of occasions, doing this very thing has saved me some serious poofage.
That's another reason why I favor separate heater and plate supplies: you can light up the heaters while limiting current to the HV supply.
I was specifically addressing the issues of primary connections, but probably should have clarified further.
Connecting two primaries out of phase cancels out their inductance whether they are connected in series or parallel with each other. What you are left with in both cases is the dcr of the windings in series or parallel as the case may be.
Connecting secondaries in parallel out of phase, same deal as with the primaries in parallel, in series fortunately they just cancel.
I have done quite a lot of work with transformers operating on both 120V and 240V. Have first hand experience. I use Hammond 3XX dual primary power transformers in most of my current projects.
Growing up overseas I replaced several dual primary transformers that inexperienced DIY'ers had series connected for 240V operation, but unfortunately out of phase. Yes they smoked, and I could still smell it when I worked on them. In no case were there wiring errors on the secondary side that would have resulted in the near instant destruction of the transformer.
Connecting two primaries out of phase cancels out their inductance whether they are connected in series or parallel with each other. What you are left with in both cases is the dcr of the windings in series or parallel as the case may be.
Connecting secondaries in parallel out of phase, same deal as with the primaries in parallel, in series fortunately they just cancel.
I have done quite a lot of work with transformers operating on both 120V and 240V. Have first hand experience. I use Hammond 3XX dual primary power transformers in most of my current projects.
Growing up overseas I replaced several dual primary transformers that inexperienced DIY'ers had series connected for 240V operation, but unfortunately out of phase. Yes they smoked, and I could still smell it when I worked on them. In no case were there wiring errors on the secondary side that would have resulted in the near instant destruction of the transformer.
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