I am trying to change the spindle acceleration rate on a 1988 Mazak QuickTurn 10N with the T3 Mazatol controller. I want to slow it down a little to reduce the peak current draw. Everything seems to work o.k., and it remembered all of its parameters and programs while it was in storage for a few months. While it was resting I was building a bigger RPC of 20hp to power it from our single phase supply to the workshop (formerly 7.5hp was the size of our RPC.)

During spindle acceleration and deceleration it would throw and alarm and go into e-stop. The voltage was dropping too much on the generated phases. After I did some balancing with the capacitors on the new setup (as I expected to do), this improved greatly, but it is still not quite good enough. Starting and stopping the spindle to 1k is fine. 2k, and you can hear the transformer hum momentarily and the cabin light dims. Do this a few times, such as while running a program and it will eventually trip the e-stop. The machine is wired back to the RPC with #2 (the installation manual says #3, and I suspect one could get away with #4). Originally the machine was on a 100amp circuit in the shop it came from. I have it on a 70amp circuit, and short of re-wiring the shop that is the best I can do for it at the moment. The single phase line to the RPC is a #6 conductor.

As I said, I am probably getting voltage drop along the #6 conductor when it pulls maximum amps, even though it should be able to handle a 70amp load. With no load on the spindle, running at 2k, I am seeing 27, 24, and 26 amps on the three legs. This seems about right. I am not tripping any breakers or blowing any fuses (the RPC has 60amp fuses protecting the floater motor), but it seems the momentary current sags and spikes during acceleration/deceleration are a problem. The machine does not shut off, just goes into the alarm state. Voltages are 228, 243, 248 no load and under the aforementioned load 225, 231, 228. Again, I thought pretty reasonable for phase balance (we have a wide range of HP motors to cater to in the workshop). We saw greater fluctuations at the previous shop from the utility between winter/summer (low voltage) and spring/fall (high voltage). I seem to recall anything from 210 to 250 on the incoming service, and the Mazak never blinked. But it did not vary except from say morning to afternoon during the summer, when everyone got home and turned on the AC. Brownouts were common in the area during the summer, and then all of the machines shut themselves down!

In the meantime I wondered about slowing the acceleration/deceleration rate down a little, as that is when the peak load manifests. I do not care if it takes the spindle a little longer to start and stop. I looked through the Mazatrol T3 parameter listing but could find nothing for the spindle acceleration/deceleration. Servo acceleration yes, spindle no. So then I had a look through the manual for the Mitsubishi FR-SX-2-11k VFD spindle controller. In there I found DIP switch SW3, positions 3,4,5 set the acceleration/deceleration time constant. Hooray I though, just the thing! 0.3 to 10 seconds are available in eight increments. It was set for 0.3 seconds. Problem is I tried all the combinations up to 10 seconds and it made absolutely no discernable difference to the acceleration rate. And yes I double and triple checked that I had the correct switches. Also the phase sequence is correct (positive), though the manual says the VFD will work regardless of the phase sequence. It has a LED that illuminates when the sequence is positive. The book says after changing any DIP switch to press the reset switch (ST1). I assume all of this is done while to power is completely off, but the book does not say one way or the other. Am I missing something? Does the Mazatrol controller not use the VFD acceleration function? Are there other parameters for the T3 than the four pages displayed on the monitor; I could find nothing in the books, and I have the full, original set.

Thanks,
Doug