Originally Posted by
drhanger
I've made some good headway into getting the spindle/amp working, but like I said before it's not completely without problems. Prior to working on the spindle I only had a couple of things needing power, including the stepper driver (now using the MX3660), the onboard power supplies (5/12VDC and 48VDC) for the steppers, the spindle brake, and the oiler. I had been using a single 120VAC garage circuit for it, which was my starting point for the spindle amp. That's where the power surge came in, tripping the breaker. I think that must have been what was blowing the 1A fuse on the amp and causing the ground fault, disabling the amp completely.
I decided to go back to using the isolation transformer, reasoning in my limited understanding that perhaps the isolation aspect of it would prevent the surge on the spindle amp, and it appears I was correct. I stripped all the old wires off the secondary, re-connected the single phase 240VAC to the primary and checked the secondary outputs. This is where one of the (possible) problems appears--the machine manual calls for 220VAC primary supply, but with the higher input voltage (my line actually reads 243VAC), I'm getting higher outputs than the labeling on the secondaries state. For example, the output labeled 115V is actually putting out 128V. I went ahead and used this as a primary power supply for the cabinet components, but I'm concerned that I may be causing some long term damage. Do I need to address this problem?
Anyway, after connecting the amp this way, everything fired up just fine--no more ground fault on the amp, and no fuse blowing. All good, except for the second problem, which is a high frequency ringing from the amp/motor, and the ringing is related to the issue of the spindle turning slowly on its own, so some small amount of DC voltage is being passed to the armature. I tried fiddling with the balance pot on the amp, and I could trim out the turning of the spindle, temporarily at least, but it changes randomly. I also noticed that with certain movements while working around the amp, the ringing changes intensity, leading me to reason again that something from the original installation was missing and needed to be replaced, but what I don't know. Page 8 of the manual (attached) shows pin 8 will disable the amp when pulled to ground--I tried that and it did work, the ringing stopped and I was able to turn the spindle by hand without any back force, so maybe that was being used as part of the original installation--there is a wire at pin 8 from the original connector, which seems to support my theory. I traced that wire back in the original schematic, and it's tied to one of the connectors on the original spindle speed board. Maybe this needs to be tied to one of my I/O's in Linuxcnc when commanding a spindle stop. Any thoughts on that?
The best news is that I was successful in controlling the spindle through Linux, including changing spindle speeds. The MX3660 includes a 10VDC analog output for speed control, but no onboard 10V PS, so I had to supply the input voltage. The manual says the input will accept 5-15V, so I connected that to the 12V PSU in the cabinet. Then I set up linux to output a PWM signal on pin 14 of the parallel port, which connected with the analog output on the MX3660. Before connecting this output to the amp, I experimented with changing spindle speeds in linux and observed the voltage on the analog output, and sure enough the voltage varied according to the commanded speed. At this point I felt confident enough to make the connection to the amp, and at last got the spindle turning with speed control!
One big concern I have with the overall project--I know from all the reading I've done that grounding properly is an important concern, and yet with all the reading I've done it's still a murky subject for me. I wonder if that may be part of the ringing issue with the amp, and what other problems may arise out of my ignorance on the subject. If anyone can advise me of what and how I should be grounding I would greatly appreciate it.