Without an external braking resistor, the deceleration is much more limited. What happens is the back EMF charges the main bus capacitor, and it will go into an overvolt error and simply freewheel to avoid charging it further to a point where it will damage the cap.
I have a 3KW air-cooled milling spindle. It had no problem with a 2 sec spinup time to 18K RPM. However, it went to an overvolt condition with a 3 sec spindown time, I had to bump it to 5 sec. The X200/WJ200 manual shows braking torque is as low as, I believe, 20%-40% of spinup torque without a resistor. With a resistor, it can be as high as 150%. From my experience with the Hitachi X200 VFD, I didn't see any visibility to current RPM. The acceleration period I had as a controllable parameter was a fixed time, i.e. 2 sec to 18K RPM but if you only specified 5K RPM target, it'd still take 2 sec. I presume that also meant if you were at 5K RPM and specified 6K it would take 2 sec to accelerate which is unnecessarily slow. And keep in mind the acceleration isn't a parameter provided with the RPM set. It would be set separately and is part of the configuration. I don't even know how to program those config parameters from Modbus. I think the manual described a 2-stage option, X seconds to RPM1 then Y seconds to RPM2. Doesn't really change things though. I didn't see an "seconds per K RPM of speed difference", as in, an ACTUAL acceleration. Danny On 3/12/2016 10:12 PM, Gene Heskett wrote: > Greetings everybody; > > Given that I note the vfd's seem to have an adjustable accelleration > control, and that my couple of hours playing with it from its own front > panel, I am led at ask the question of just how fast can one of these > things be reversed from say 1000 rpm at the motor spindle? > > I ask because my present setup, using the OEM PM DC motor which is all > gear drive to the spindle, one of Jons pwm servo amplifiers and a 125 > volt dc supply, reversals at the turn around depth of this cycle of a > peck tapping operation, with the spindle doing 300 rpms, is a very small > fraction of a second, far less than 30 degrees of rotation. Based on > its reversal performance at 2500 rpms being a slim second, I am > concerned that the vfd may not be able to reverse so quickly, and will > impact my use of G33.1 because of the turnaround over shoots. On my > lathe, with its fragile drive train and a 5" chuck, this overshoot is > between 2 and 3 turns at 250 running rpms. Usable, but if I don't stop > it soon enough, the tap may bottom out and break. > > What has been the experience of others using smaller vfd's and motors? > > Can you still do rigid tapping safely? > > Thanks all. > > Cheers, Gene Heskett ------------------------------------------------------------------------------ Transform Data into Opportunity. Accelerate data analysis in your applications with Intel Data Analytics Acceleration Library. Click to learn more. http://pubads.g.doubleclick.net/gampad/clk?id=278785111&iu=/4140 _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
