Tuesday, April 5, 2011

Fan Drives: High Start Up Loads and Synchronous Belt Drives

Start up loads can be a significant concern when evaluating potential drives for conversion to PowerGrip® GT®2 or Poly Chain® GT® Carbon belt drives.  PowerGrip® GT®2 and Poly Chain® GT®Carbon belt drives will transmit all of the start up torque, where V-belts may slip if the load is excessive.  Due to the inertia of the fan, start up loads can potentially be 150% to 200% of the normal operating load.  This is obviously much more of a concern when the drive will be operating on a system that frequently cycles on and off.  Drives that run continuously will only see the start up load intermittently, so are not as sensitive to the combination of high start up loads and weak structures.  It is important that the start up load be considered when evaluating a drive.  If the structure is weak, a high start up load will further adversely effect the PowerGrip® GT®2 or Poly Chain® GT® Carbon belt drive's performance by allowing center distance collapse.  This reduction in center distance results in an under tensioned belt which may wear prematurely from being undertensioned, or even worse, premature failure from ratcheting.  If an electrician or properly trained technician is available, an ammeter can be used to compare the start up amperage to the steady operation amperage.  If the amperage is 1 1/2 to 2 times the steady state amperage, the structure should be carefully inspected to insure that it is robust enough to prevent center distance collapse upon start up.  With the drive shut off and safely locked out, the structural rigidity can be checked by pushing the two belt spans inward toward each other and looking for any relative movement in the structure.

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