Re: How are 240 VAC variacs made?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: Finn Hammer <f-h-at-c.dk> 

John,

Yes, I have it in my power controller.
Perhaps it helps to show the wiring like this, it is just rearranging the 
schematic by flipping one variac 180 degrees:

             9                   9                      9 <---
             9                   9                      9
      -------9            -------9 <---          -------9
       ^     9             ^     9                ^     9
       |     9             |     9                |     9
       |     9             |     9                |     9
       |     9             |     9                |     9
       |     9             |     9                |     9
       |     9<---         |     9                |     9
       |     |             |     |                |     |
       240V  |    0V       240V  |  240V          240V  |  280V
       |     9<---         |     9                |     9
       |     9             |     9                |     9
       |     9             |     9                |     9
       |     9             |     9                |     9
       |     9             |     9                |     9
       v     9             v     9                v     9
      -------9            -------9 <---          -------9
             9                   9                      9
             9                   9                      9 <---

In this case, the wipers are moved out from the center, till beyond the 
240V tap point (or 120 tap points, if you like)

Tesla list wrote:
>Original poster: "John H. Couture" <couturejh-at-mgte-dot-com>
>Finn -
>Have you actually tested this wiring setup? I believe you will not get the
>280 volts with the setup you have shown which is a short circuit across the
>output.

Only in the shown position, which is also the 0 Volts position.
But ordinary variac`s short the output too:

             9  <---possibility of 280V
             9
240-------- 9
             9
             9
             9
             9
             9
             9
             9<-----------0
  0-----------------------0


If you move the two wipers to the other ends of the windings you
>will get a lower voltage.

No, this is where I get the 280 V

  If the 240 volt input is grounded there will also
>be differences in the voltage vectors to ground.

It may not be a smart thing to ground the intermediate feed from variac, 
thru` current limiting inductor, to stepup transformer.....

However, I do not have two
>variacs to make any tests.

You don`t have to, I`m sure you can see it with the new drawing.

Cheers, Finn Hammer


>             +----------9 <----------------
>             |          9            ^
>             |          9            |
>             |          9            |
>             |          9            |
>             |          9          0-280V
>      -------)----------9            |
>     ^       |          9            |
>     |       |          9            |
>     |       |                       v
>     |       +----------9 <-----------------
>    240V                9
>     |                  9
>     |                  9
>     |                  9
>     v                  9
>     -------------------9
>                        9
>                        9
>The "9`s" are the windings.
>If morale is high, he connects them on the same shaft, but this is not
>necessary.
>
>Cheers, Finn Hammer
>