Build Thread- Cadillac NC100 Servo Control Power Conversion 3PH 60VAC to 60VDC

[NICKKINSMAN]

I am in the process of retrofitting a Cadillac NC100 with Fanuc 5T control (circa 1980) to modern computer control. I have nearly everything figured out except this:

I have 3PH 60VAC Power from the origianl transformer, so I can get 60VAC power, but need to convert it to DC.

Apparently this conversion was done via a diode setup in the actual controller of the original. It also appears the diodes are variable and were used to control the speed.

I only need to get full 60VDC voltage out of it, to feed my new MESA servo board which will control the power.

if anyone has any suggestions let me know. I have attached a picture with descriptions on what is on the diode board. My original thought is to strip out this diode board and use it, but just putting power to it is getting no output, guess the diodes need some input in order to pass the power. Question is what input and how much to avoid damaging them.

Thanks!

Nick

[NICKKINSMAN]

If anyone else runs into this issue, I was able to figure it out, a simpler way is to use several bridge rectifiers to conver the 3PH AC to DC. You could use this same board to get the full power by replacing the varistors (variable diodes) with straight diodes and only using diametriaclly opposite banks, as they are setup for reversing in the original unit, but you would do the reversing in the control board.

[Al_The_Man]

If you want to convert the SCR control to regular rectification then use a three phase bridge, however if you need the supply for PWM drives etc, you will need capacitor smoothing, this will raise the DC level to ~84VDC.
The capacitors do not need to be that large for rectified 3 phase as the % ripple is alot lower.
Al.