On Wednesday 23 December 2020 19:55:48 andrew beck wrote: > Just to tag in. > > I need a braking resistor for my cnc mill spindle it's a 7.5kw vfd. > Need pwr src voltage etc, and I'll look it up in the Huanyang book.
> Needs to rigid tap all the time etc > > Any ideas? I like the idea of a stove element.. > > Just need to know some values etc > > On Thu, Dec 24, 2020, 7:52 AM Chris Albertson > <albertson.ch...@gmail.com> > > wrote: > > Yes, as I wrote above, the resister specs depend a lot on how often > > you intend to reverse the direction of the spindle. And how > > quickly. > > > > A resister of "infinite" resistance (open circuit. eg "no resister > > at all") can work but will give lower performance braking power. > > This would be "good enough" for many cases but maybe the intended > > usage is to do rigid tapping on thousands of holes at the highest > > possible rate in a production environment. > > > > I think in this case, just compromise. A resister at the higher end > > of the resistance range would not need so many Watts rating. > > "i^^2*r" will tell you. > > > > > > On Wed, Dec 23, 2020 at 5:50 AM Todd Zuercher > > <to...@pgrahamdunn.com> > > > > wrote: > > > I doubt you'd really need a braking resistor for running a router > > > spindle (what I believe you have.) Simply test it without one, as > > > long as you don't get overvoltage alarms on the VFD when > > > decelerating you should good without it (assuming your VFD has > > > adequate safety alarms which might be a big assumption with a > > > Chinese piece.) > > > I've not run into a machine that uses one myself, but I only work > > > with large commercial router machines. (not any mills or lathes) > > > and router spindles don't have the rotating inertia that other > > > machines like a lathe might or the need to stop super fast. > > > > > > Todd Zuercher > > > P. Graham Dunn Inc. > > > 630 Henry Street > > > Dalton, Ohio 44618 > > > Phone: (330)828-2105ext. 2031 > > > > > > -----Original Message----- > > > From: Jon Elson <el...@pico-systems.com> > > > Sent: Tuesday, December 22, 2020 8:51 PM > > > To: Enhanced Machine Controller (EMC) > > > <emc-users@lists.sourceforge.net> Subject: Re: [Emc-users] > > > Checking vfd hookup question? > > > > > > [EXTERNAL EMAIL] Be sure links are safe. > > > > > > On 12/22/2020 06:30 PM, Matthew Herd wrote: > > > > In my research on resistor sizing, I heard reports that Haas > > > > uses stove > > > > > > elements for their braking resistors. On factory machines, no > > > less. Of course that’s second hand, so I can’t say it’s true. > > > > > > > > > Yes, absolutely. Our Haas at work has a stovetop element in a > > > screen guard on the back of the machine. > > > All of them are made like that. It is a perfect solution for a > > > 240 V machine. But, for the smaller VFDs you want a small > > > stovetop element so > > > > it > > > > > doesn't draw excessive current. Assuming a voltage doubler on a > > > 120 V VFD, it will still have 340V or so DC on the DC link, same > > > as a 240 V VFD. A 40 Ohm element should draw less than > > > 10 A, which should be safe for anything but the smallest VFD. So, > > > get > > > > the > > > > > 7" stovetop elements, not the 11" ones. > > > > > > Using too low a resistance won't harm the MOTOR, it will blow the > > > power brick in the VFD. > > > > > > Jon > > > > > > > > > _______________________________________________ > > > Emc-users mailing list > > > Emc-users@lists.sourceforge.net > > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > > > > _______________________________________________ > > > Emc-users mailing list > > > Emc-users@lists.sourceforge.net > > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > > -- > > > > Chris Albertson > > Redondo Beach, California > > > > _______________________________________________ > > Emc-users mailing list > > Emc-users@lists.sourceforge.net > > https://lists.sourceforge.net/lists/listinfo/emc-users > > _______________________________________________ > 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
