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In parallell with working
on the servodrives, trying different models and figuring
out that damn encoder trouble I worked on the
powersupply. I designed it for 130VDC since that would
give me a nice margin regardning PWM dutycycle of the
drives and IR-losses etc, yet stay well below the
maximum terminal voltage of the motors which is 170V.
I ordered a new 4kVA
3-phase transformer with 90V secondary, this would give
me roughly 130VDC after rectifying and filtering. I also
designed an powerdump circuit that prevents the voltage
in the powersupply capacitors to rise above the rated
voltage due to them be charged by the current returned
to them when the motors decelerates.
  
I designed the PCB to
fit on top of the two 15000uF/250VDC capacitors and it's
made with 105um copper on each side so it can handle the
current without problems. I used my
DIY machine to cut and
engrave a cover in lexan. When the powersupply voltage
goes above the setpoint (I have it set at 140V) the dump
circuit activates and the MOSFET connects two 15ohm 100W
resistors in parallell (not shown in these photos)
across the powersupply, effectively loading it with
~18A. This prevents the voltage to rise more than a few
volts above 140V even during rapid deceleration.
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