Back to back autotransformers for B+?

[v4lve lover]

some of those autotransformers do posses galvanic insulation . but its better just to get insulation transformers for 240/380 .


valve

 

[Printer2]

Bought a couple of autotransformers real cheap online. One piece of wire that they loop out somewhere in the middle to get the lower voltage tap. Being that they were cheap they did not put any varnish on the windings. With a bit of care I managed to get one unwound to the middle point. I then cut the wire and rewound the wire onto the first winding. In order to isolate the windings I insulated the space between the windings with card stock and electrical tape. Since I am not pulling the rated power from the transformer I have not had any problem with overheating. The insulation on the wire should be just fine as it is new wire, has not been heated, and the bends were not sharp over the previous windings. Also the voltage difference between the windings is not all that great between layers if you are laying one layer over the other.

The second autotransformer had a winding flaw where the wire was stick under the previous windings and I could not unwind it without breaking the wire. Can't complain though as I only spent a couple of bucks for them. I would not bother doing this again, just wanted to see if I could low buck an amp.

 

[Aiace]

If there is no load on the final windings there will be no current between the two transformers, as long as the secondaries are rated at the same voltage.

Simplistic, I appreciate that there will be the magnetising current which is minimal.

I think you need to read up on transformer theory.

What you are saying is akin to saying that any transformer will overheat with the correct voltage applied - utter rubbish.

Ok, you have studied right but you've have stopped at the ideal model of the transformer.
keep up studing.....the next story it's more interesting

 

[KatieandDad]

Ok, you have studied right but you've have stopped at the ideal model of the transformer.
keep up studing.....the next story it's more interesting

I've built transformers.

If the Flux Saturation is calculated correctly, as it should be of a commercial design, then each winding will be capable of handling Vp or Vs (its immaterial).

Some commercial transformers tread very closely to the 1000mT maximum, a good transfomer will operate at less than a third of this value 320mT.