On Sunday 13 March 2016 00:19:35 Danny Miller wrote: > 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
Thanks Danny. I'll have to investigate the little booklet manual that came with it to see what sort of a braking R is needed, and a wild guess at what its wattage would need to be to survive a 50 peck g33.1 hole tapping session. I think it mentioned it, but it wasn't something I was concerned about at the time I was verifying that it would at least run. I haven't used a braking R per sei with Jons amplifier, but I do know it will dump back into the supply, blasting it from 125 volts to enough to clear a 7 watt 127 volt night light style of a C7 lamp in just a few cycles of that. I hadn't even considered the need for the braking resistor, so that will obviously need to be arranged for. Glad you brought it up, thanks. > 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 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) Genes Web page <http://geneslinuxbox.net:6309/gene> ------------------------------------------------------------------------------ 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
