"All the time?" When you have a hard requirement like this is when some detailed engineering can pay off. Assume you are reversing at 50% duty cycle and burning 1KW 50% of the time. Where I live this can cost 12 cents per hour. This is $89 per month if you actually do run "all the time". Or $1,000 per year. Or maybe you are usig a lower value resister and burning 4KW with your brake? That is $4K per year
A better way is to use a battery inside the power supply. a 100 amp-hour lithium battery would cost possibly $400. Then the braking energy goes into the battery and then a few seconds later the battery is used to run the spindle in the forward direction. The battery needs to be sized so that the energy transferred each cycle is small (maybe 1%) of the total capacity. The power supply only has to supply power to overcome friction. Most of the energy to accelerate the load comes from the brake. This is exactly how a hybrid car works. They are most efficient with batteries that work at about 400 volts or more. THis said, I doubt anyone is actually going to run a 7.5KW motor at max performance forward reverse cycles for hours on end. But if you do running a stove element is not cheap. It is really not very complex to brake with a battery as long as the battery is very large relative to the current. A double H-bridge is all you need. On Wed, Dec 23, 2020 at 9:23 PM Scott Harwell via Emc-users < emc-users@lists.sourceforge.net> wrote: > THE Huan Yang 7.5 requires 1000 watt at 75 ohms. > > > > > 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 > -- Chris Albertson Redondo Beach, California _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
