On Saturday 16 May 2020 12:53:29 Curtis Dutton wrote: > I believe that I'm having trouble understanding how to set an 8i20 up > properly. > > It is connected to a 2.5KW 200V AC servo which can take a maximum > current of 44.5 amps. Maximum speed of 5000RPM. > > It is running a lathe spindle. I am able to get it to spin up but it > seems a bit sluggish. I also would expect, when setting the current > value to maximum output that I would see current-lim go true but it > doesn't. > > NVMAXCURRENT = 3000 > current-maxlim = 30 > current-minlim = -30 > current-scalemax = 1 > > > 8i20 voltage says 350 ~ 351 > voltage drops to 340 while accelerating. I have 10 GA wires from the > power supply to the 8i20 which are about 8" long. The power supply is > an ELMO Tam-20/230 with a peak of 40A power output. > > > I've tried to look for some documentation explaining exactly how those > values work, but I can't seem to find it. > > Thanks, > Curt
Generally, for snappy response, you will need at least 2x the rated current available to supply the surge needed for quick response. And lots more capacitance to supply the surge needed to accelerate it smartly w/o haveing a huge sag on voltage. Mt guess, since the drop is not obviously large is that the controller is limiting the current to protect itself. My G0704's stock spindle motor is rated at 90 volts and 9.7 amps to develop its rated 1 horsepower. But the psu I built for it, basicly out of my scrap box parts, has a 126 volt output and enough microfarads worth of filter capacitors that from a cold start, can and has tripped a 30 amp breaker from the 126 volt line, so it gets 3 seconds worth of a soft start limited by a 50 ohm 200 watt resistor to get the caps somewhere near to a working voltage before the the 2nd SSR closes, bypassing the resistor. Originally supplied with a puny scr based controller by grizzly, could run it 2250 revs on a really good day, its remains are in that same junk box now, and one of Jon's Pico Systems pwn-servo amplifiers, which is a full 4 quadrant controller, now runs that spindle at 3000 revs, but being a full controller, it can pull that energy back out of the motor, running all that capacitance up to around 165 volts peak, and the stop which is detected by a one shot on an encoder leg, then allows the change in direction to get thru to the controller, which also releases the speed stop and spins it back up using that stored energy in the capacitance to spin it back up in the opposite direction. All in about 400 milliseconds and not tripping the 20 amp breaker in that slot of my service now. Your 40 amp supply is too little, too slow. But the controller is probably most of the sluggish. With lots more microfarads, it might get the job done better. 80 amps would be even better but probably would be more than the controller can tolerate even for the short term needed to get that snappy response. That supply I built, has around 140,000 microfarads of storage capacitance, on purpose to supply the surge needed to manhandle a big motor. Jon's pwm-servo is set to current limit that 9.7 amp motor at about 17 amps, and I hear the iron in the motor squeak from that limit being hit for maybe 50 milliseconds while its doing that turn around. Sure, if it continued for any length of time it would be hard on the motors brushes, but in normal service its maybe .0001% of the time, and no brush maintenance has been needed in about 4 years now. That turnaround is profiled by a limit3 in front of the PID, so both the decel and accel times are controlled just enough the Z can keep up if doing a rigid tap with a tap big enough to need a peck cycle. You might even consider putting the circuit breaker downstream of the supply, between it and the capacitance so the surge currents won't cause some "nuisance" trips. That will however, still subject the controller to the surges, which it must be able to handle with aplomb. Bear in mind that at that power level, an accidental short with a screwdriver will remove a good sized piece of the screwdriver and your eyes will suffer spots for quite some time. Use common sense around such stuff. If you aren't comfortable doing it, don't!!!!! Get someone who IS qualified and pay his fee with a smile. I wouldn't even think of advising on this if I weren't a C.E.T. and a retired broadcast tv engineer, used to dealing with transmitters drawing 250 kilowatts at normal song. Respect it folks, its made several passes at frying my ass but I am a survivor. Don't ask why, he hasn't told me yet. I once came across a hot, smelly kearney bolt, holding 4 strands of 750 MCM cable together, carved the insulation off the cables beside the hot one with my pocket knife, went to town and got another bolt, and several rolls of scotch 88 to tape up a new 24" crescent wrench handle I also bought, and installed that 5 lb kearney bolt beside the hot one, all while that cash cow was on the air. Why didn't I shut it off? Couldn't, building way too old for NEC rules, no entrance breaker, that bolt was connected directly to the substation pole with 3, 50 kw cans on it. And it was all just in a days work to me. Was I comfy doing it? Not no, but /hell/ no, but it needed to be done and there wasn't anybody else to do it. Transmitter sites are usually lonely places on top of whats called a mountain. Having seen quite a few mountains from a top view, thats just a hill, and at 1600 ft, not even a big one. > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) If we desire respect for the law, we must first make the law respectable. - Louis D. Brandeis Genes Web page <http://geneslinuxbox.net:6309/gene> _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
