Gestas (Customer) asked a question.
I'm designing a mill, I'm going to use dynamic braking on several axis using WEG CFW500s. I'm concerned that I'll overheat the breaking resistors, a mill spindle needs to stop fairly frequently. I'd like to use a cold plate, something like this - https://www.boydcorp.com/thermal/liquid-cooling/hi-contact-liquid-cold-plate.html.
The spindle requires a ~1200W, 15 ohm resistor. All of the resistors I can find in this size are cylindrical and use standoffs to raise them up, see GS-BR-1K2W015 as an example. There isn't a way to attach these to a cold plate.
Are there resistors in this size that have a form factor similar to GS-BR-300W070? Is there another way to prevent overheating? I can run a fan in the enclosure, would that be enough? Would it help if I oversized the resistor, I could use a 2000W resistor.
Thanks, C
My mill is relatively small and has only a 3.5kw spindle on a VFD. I don't believe it has any sort of cooling directly on the braking resistor, so I doubt you will really need one. If you are really worried then just put an enclosure fan blowing directly onto it. That should easily cool it enough.
One of our machines has a servo that whips around at its maximum speed to get back to home and stops very quickly. It required a braking resistor and we put one of these on it:
https://www.automationdirect.com/adc/shopping/catalog/drives_-a-_soft_starters/ac_variable_frequency_drives_(vfd)/braking_units_-a-_resistors/gs-2010-br-enc
They also sell a larger version that is rated for 2x the spec you need:
https://www.automationdirect.com/adc/shopping/catalog/drives_-a-_soft_starters/ac_variable_frequency_drives_(vfd)/braking_units_-a-_resistors/gs-2015-br-enc
These have three of the circular resistor coils inside the case, and you could either place fans blowing through the case or you could use multiple waterblocks mounted to the back and possibly front and cool the case down that way. The resistors bleed heat from the coils to the outer case and it does get warm, so by cooling the case you would be somewhat increasing the rate that the resistor coils inside cool down/give them greater capacity.
The description for the gs-2015-br-enc says it's for a DURApulse motor. I looked at the wiring diagram and installation instructions, I didn't see any reason it couldn't be used with any VFD. Does that sound right to you?
Yes, you should be able to use it with any VFD or servo that has two terminals for a braking resistor and has parameters that can be set to the wattage and resistance of the BR.
Awesome, I appreciate all your help. Thanks.
For anyone that comes across this in the future I found another potential solution. It's possible to wire multiple, smaller braking resistors together to meet the total resistance requirements. This is how the DURAplus braking resistors are implemented.
Depending on the details you may need to wire the resistors in parallel, series, or both. This PDF, starting on page 11 does a great job describing multiple different topologies. The theory is covered here, Resistors in Series and Parallel.