Hi John, Sorry for the delay - just got back from a meeting. I also updated my email address so I can post again!! My ISP moved to Google services and my email address changed. The EMC list had blocked posts sent from my new address.
I'm guessing your 2.5" facing mill may not be rated at 7.5kW average with peaks of 15kW during acceleration and deceleration. Does your facing mill have electronic drive controls or is it a plain 3-phase motor with belt reduction? I'm guessing our 7.5kW spindle drivers were built with the assumption there is a sturdy 3-phase supply to lean on. I posted a picture at: [LINK: http://flic.kr/p/c8pc7Y] http://flic.kr/p/c8pc7Y showing the circuit mod. I forget the exact resistor and capacitor values but I just experimented with a 5k and 220uF pair with a 10V bench power supply. To reach 90% of full value (9.0V) it took 5 seconds. Using a 1k resistor with a 220uF will reach 90% of terminal value in 1 second. My selection gave me about a 2 second time constant. Just now I emulated the Heidenhain 0-10Vdc control with a bench power supply. Connecting the resistor to the cap to limit the rate of voltage rise on the capacitor and watching the cap voltage reach 9V took 5 seconds with the 5k resistor. I remember inserting a resistor first and making sure the stepped speed program still achieved the RPMs I wanted it to. If you program it for 2000RPM and it only hits 1500RPM then choose a small resistor value. Somewhere in the 100 ohm to 4.7k ohm should work. If the resistor is too high a value compared to the input impedance of the spindle driver you will simply have a drop in voltage at the spindle driver and never achieve the speed you want. So, start with 1k without the capacitor and see if that changes your spindle RPMs. If ok then add (1) or (2) 220uF capacitors to suit. This will add 1 to 2 seconds of delay to slow the acceleration and deceleration of the spindle. If your spindle driver is analog like mine you may have a good chance of modifying your machine too. Old analog is great. No digital protocols or acknowledge packets to mess with. If you have schematics to the CNC controller, look for the spindle interface lines. If there is just one or two shown, you can break the connection and manually control the spindle speed with an external bench supply, potentiometer, etc. My experience was pretty straight forward looking back on it. It was the first rotary phase converter I built. When accelerating OR decelerating quickly, the spindle power meter would max out at 180% (meter would peg). This is normal for this machine. Accelerating would decrease the CNC's voltages and decelerating and dumping the spindle's brake energy into the rotary phase converter "grid" would increase the CNC's system voltages. It was apparent to me that is was starving for power while quickly accelerating and I did not have a strong enough grid (rotary phase converter) to brake against. If the engine is too big for a car and starved for gas or if the tires break loose while downshifting then don't accelerate as fast or decelerate as fast. The RC delay fixed it. Let me know what you find in your schematics. Dennis >Hi Dennis, >I have a 2.5" diameter facing mill that I use and I don't notice any >difference when using that. My machine lights do not dim during >acceleration which I assume is a good thing. I'm in the same canoe as >you with 240v single phase my only option to work with. > >Before all the experiments I could get 0 to 2k with no problems and >would structure my programs around that or use the G4 pause and ramp up >to the rpm I wanted above 2k. > >I too modified my program using a pause between S values but only had to >do that going up in rpm. From 6k to 0 I've never had a fault. > >The resistor/capacitor would be a low cost experiment. How do you >calculate what the values are for the resistor and the cap? Did you put >the resistor in series with one of the control lines? Does the cap >connect to the upstream side or the downstream side of the resistor? >Maybe a stick drawing would help me understand... > >John ------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
