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AC motor VFD panel design

AC motor VFD panel design

AC motor VFD panel design

Dear Sir

I have an older piece of industrial woodworking equipment that was originally equipped with a 5hp, 4 speed 3ph feed motor. At some point in time it was replaced with a single speed motor. I am convinced that the way to remedy this is to install a variable frequency drive. None of the self-contained drives units that come installed in NEMA 1, 4, or 12 enclosures will work because of environmental considerations. The machine is in a location that is exposed to sub-zero temps and overheating in the summer, also condensation is a problem. The solution is to purchase drive separately and install into a proper size NEMA 12 enclosure. The enclosure can be equipped with heater, thermostat and circulating fan. Do you have any suggestions on how I would size up this cabinet keeping it to a minimum and yet not so confined as to excessively build up heat? There are many drives available and all that I have researched to this point have similar working parameters of which I exceed. The temps in the area that this machine is located range from -20F to 95F. Maximum drive temp is not to exceed 140F and in most cases not fall below 15F. Heating the enclosure during the winter months isn't the problem; a small cabinet heater and thermostat easily maintain the minimum. The problem is in the summer months where temps in the area of the machine reach 90F, I'm not really certain how much heat will be generated by these 5hp rated drives (208v 17amp). An internal fan would help move the air in the enclosure and prevent hot spots but I'm not certain it would sufficiently cool considering the amount of heat generated during operation?? The next and perhaps better solution would be a fan/vent/filter combination that could be activated by a high limit thermostat. The problem with this is maintaining a clean filter because of the somewhat dusty conditions, so totally enclosed would be preferable if workable.

Also, drive requires "J" class fuses for motor & drive protection. I don't understand why they are asking for fuse size to be 40 amp? Shouldn't protection be a max of 150% of motor full load when using time delay fuse? Is this "J" class fuse a time delay for motor startup, or is it likely just for short circuit protection with rating calculated at 250%?

Any direction that you could give me would greatly be appreciated.


RE: AC motor VFD panel design

Mr Handy
I believe you might find an answer on the Hoffman enclosure website. http://www.hoffmanonline.com/.
They used to have a downloadable program that can assist in determining an enclosure and cooling. I am also sure they could assist you directly as most any other enclosure manufacturer would. You should be prepared with complet tech. info on your system components. KW HP mtr ratings etc...

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