Amazon 660533 8 inch large surface element 2600 watt $15.89 us.
It should be popular during the winter.
On Wednesday, December 23, 2020, 8:17:03 PM CST, andrew beck
<andrewbeck0...@gmail.com> wrote:
Just to tag in.
I need a braking resistor for my cnc mill spindle it's a 7.5kw vfd.
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
> >
> >
> > _______________________________________________
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> >
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> >
>
>
> --
>
> Chris Albertson
> Redondo Beach, California
>
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