Can this be used as an Autotransformer or will it be an SDS

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210520-2140 EDT

synchro:

If you have a center tapped winding with the center tap connected to one end of a voltage source source, and an outer end connected to the other terminal of the said voltage source, and place a load across said two terminals, then that load can be as large as the primary power source can provide.

Loading from the center tap to the opposite end uses the the transformer as an isolation transformer, but having two ends of the two coils electrically connected. Changing the phasing of one of the windings does not change this.

However, if you use the transformer as an autotransformer, you have the functional results of it being an autotransformer.

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I was saying that the secondaries should be wired in parallel, and that paralleled secondary be wired with one end tied to the source neutral. The other end becomes the second line so you'd have a grounded-center-tapped 120/240v supply.

The primary has to be fed at 120v because that's all that's available. The derived half of the 120/240v supply is limited by the transformer, while the other half is limited by the source (minus energizing current, of course) just like a buck-boost.
 
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LarryFine said:
I was saying that the secondaries should be wired in parallel, and that paralleled secondary be wired with one end tied to the source neutral. The other end becomes the second line so you'd have a grounded-center-tapped 120/240v supply.

The primary has to be fed at 120v because that's all that's available. The derived half of the 120/240v supply is limited by the transformer, while the other half is limited by the source (minus energizing current, of course) just like a buck-boost.
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That's exactly how I was interpreting your earlier post.
 
LarryFine said:
I was saying that the secondaries should be wired in parallel, and that paralleled secondary be wired with one end tied to the source neutral. The other end becomes the second line so you'd have a grounded-center-tapped 120/240v supply.
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For what purpose? He's got a 120V circuit and needs it to be 240V to supply the equipment. There's no need for a grounded-center-tapped 120/240V supply.
 
While I agree that this transformer _could_ be connected as an autotransformer, and _could_ be connected to either provide 120-0-120 or 0-120-240, I'd like to point out that the transformer diagram shows a grounded electrostatic shield between primary and secondary.

Using this transformer as an autotransformer would bypass that shielding. (Of course, connection to a GEC and grounding electrodes might also bypass this shield if the grounding electrodes are common with the source.)

I would confirm that the isolation between primary and secondary was not one of the reasons for recommending this particular transformer prior to using it as an autotransformer.

-Jon
 
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