90VDC Motor Controller

[jsteve126]

I am currently trying to build a speed controller for a 90VDC motor. Please see the attached schematic. My  question is; should GND and GNDB be connected directly or should there be some kind of isolation?
I thought that a common GND would be necessary and bread-boarded it that way. It seemed to work; until I connected my microcontroller programmer, which is connected to my PC, which is earthed. This tripped my house's Earth Leakage Breaker. Result, no power in the house. Something obviously is not right, and I am hesitant to try this high voltage stuff again until I can get some help on it. 
Any advice would be greatly appreciated.

View attachment 41603

 

[Hero999]

It's a dangerous design. The DC side should be isolated from the AC.

The easiest solution in this case is probably to use an optically or pulse transformer isolated TRIAC to perform phase control on the AC side of the rectifier.

 

[jsteve126]

Thanks hero999. Yes, it does look dangerous. I should say that the ac-dc motor drive part is not my design. I took this from an existing motor controller PCB that I have. It is all self contained, ie. just power cable and one pot for speed control. I want to add control from my PC.
I am thinking of using a wireless serial connection. Do you think this would be safe enough? 
Getting back to the first question. You mentioned phase control on AC side. I've tried searching for info on this, but all I find are examples that use AC motors. Could you possibly point me in the right direction with an example link or two?