Torroids are remarkable things to work with .. everything about them is wonderful... except winding the things.
If you want to take turns off ....... without invasive surgery ( 240 winding looks to be internal winding) you need only wind a few turns in the opposite direction..... on the outside...... and you have it........ so easy with torroids. Same with the LV windings, but physically more difficult as they are lots in hand wire.... so they are very easy to "tune".... we pay a price of more copper and associated R, but in this case, it will be in the HV side, so not as critical as the LV high current side. I haven't messed with the PJ transformers, but assume they only run 2mm wire on the HV side.... so easy to wind turns on the outside and change things.... up or down.
So every turn in the opposite direction nullifies that many original turns, any added turns in the original direction, adds to the original winding..... so you can see we can modify without messing the original one up. ( this assumes we series the new turns with the original winding).... so try it, wind a dozen turns around the 5kw units tranny, and series these turns with the 240v winding.... first one way, then the other and see the difference. ... they add or subtract....... now thats quick and dirty fix...
The stacking is very useful too. Same idea. If you strip all the multi core winding off the outside, it leaves only the 240v inner winding on the core. If we have two of these the same,we simply stack them one on top the other.... totally separate from each other.. just physically piggy backed. If they are not the same we can "tune "them as above.
Now we simply wind our LV winding around both of them, treating the new twin stack core as a single entity....... we then parallel the HV windings for twice the power handling in the HV side, and we have a new transformer, twice the power, lower resistance than if we had two separate ones in the LV winding because the winding path is now shorter... where we have the two stacks touching each other.... there is no LV wire ... just the original HV wires.... so we have saved that by 2 times.
We now have 1/2 the turns on the LV winding, as it now encompasses twice the core area than original, so half the turns, and so we can now double the wire cross section to make up for that...... we get a more powerful transformer as we have shortened the wire path, so resistance goes down, as does temperature.
We can strip off the HV windings too, and glue the two cores together, and we free up more wire length, ( where the cores are glued...no wire, so we have saved those parts of the turns from each core... we have to wind only half the turns now, as we have doubled the core cross section area, so less turns to tussle with ( doubled the volts per turn)... now we are getting a big saving is space and resistance... and easier on the bloke winding it too.... can you see how much wire gets saved when you three stack... starts to get seriously good... 4 lots of wire sides are taken out of existence.... thats an entire transformer worth of wire saved for the same result, so the R heat of a whole transformer is now gone... and thats I^2R heat too.... thats how my big one is wound... three massive torroids.
Remember, with torroids it is only the wire in the core space that does anything useful, all the rest of it just gets it back into the core for the next turn.... ie three out of four sides play no part in the transforming, only the inner wires count, the rest is just resistance we suffer... all the magic happens in the hole in the middle.
Will do a mock up tomorrow as demo if I get time, and it will become clearer.
