variac based symmetric bench power supply

[cakyol]

In trying to simplify this design, does anyone see an issue with eliminating the isolation transformer and instead, driving the rectifier directly from the variac outputs ?
I know mains isolation would not be achieved, but other than that, are there any other issues ?

I added the new diagram.

 

[bansuri]

There will be exactly 0V between your slider outputs no matter where you adjust the variac. you put them in parallel.
The DC voltage is only half of what you expected. It will not be balanced either

 

[cakyol]

Sliders will be moving in opposite directions, not the same direction

 

[johnmath]

If they were moving in the same direction there would be a near constant voltage of ½ Vmax on the bridged output.

 

[cakyol]

That is why I emphasized that the sliders will be moving in opposite directions to create an increasing voltage.

Apart from that, if a GFCI is used, any dangers in not using an isolation transformer ?

 

[johnmath]

Without the isolation transformer any grounded object can provide a path for current from either output. If you want to achieve a level of safety against electrocution when working on live equipment there is still a need for an isolation transformer.

 

[bansuri]

when the sliders move opposite, on 0° and also at the end is full voltage, and in the middle half. Not useful either

 

[chrisng]

I like your idea @ post#14 better. Since you already have the 1kVA toroidal transformer, will be cheaper to buy a single gang variac than a dual gang, and it's isolated. BTW, not sure how accurate are the two outputs of the dual gang.