The brake resister depends on what duty cycle you run the motor at. It you only run forward at a constant speed you will never use the resister. But if you continuously run the motor to full forward then full backward speed for hours you will be heating the resister with about 50% of the motor's full power So over 1KW. Then add a "safety factor" or say 1.5 and you get a 1.5KW resistor. But I doubt you'd do a worst-case back and forth motion.
One way to save a few $$ is to install a fan in the resistor with a thermostat. The best load resisters I found per dollar are those ones on eBay made with wires over a ceramic tube. Buy several and you can adjust the resistance by writing series/parallel in different combinations. A low resistance will be a more effective brake. But do not go too low. Calculate the current. If the motor has 200 volts across it and you sort the leads through a 1 ohm resistor then you get 200 amps and maybe the motor is only rated at 20 amps and you blow up the motor. The most efftive brake is a length of wire. The worst one is an open circuit. I think maybe a compromise is to use a resister then same inpedence as the motor. I knew some one who found he could use a stove heating element as a load. They are cheap Wild guess? maybe 50R at 1 KW peak with much lower average W ratiing. On Tue, Dec 22, 2020 at 3:25 PM Gene Heskett <ghesk...@shentel.net> wrote: > Greetings all; > > Swapping a 110 volt vfd, for a 250 volt vfd, one of the terminals is > labeled differently, the common point of the fwd/rev/spd1-2-3-4-5 > terminals on the 110 volter is labeled XGND > > But the common point terminal on the higher voltage unit is labeled DCM > but the diagram of how to hook up external controls is identical. > > Is there any good reason to treat it differently in hooking it to a > 7i76D? It should all be equ as its the presence of continuity from the > fwd/rev terminals to this XDNG/DCM common point that determines the > command. > > There is no terminal labeled neutral on this controller, only a marked > static ground which I ran back to the services static bar, not to the > neutral bar. But my copy of the NEC is now 24 years old, so I'm asking, > hopefully, someone with a more recent copy. > > This is also the first vfd I've had that actually has hookups for a dump > resistor. 2.2 kw vfd & motor, running on 250 volt single phase, what is > good value and wattage for this resistor? > > Thanks folks. > > 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 > -- Chris Albertson Redondo Beach, California _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
