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Thread: 2hp VSD on 1/2 hp motor
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23rd Jun 2015, 09:48 AM #1Most Valued Member
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2hp VSD on 1/2 hp motor
I need to ask the experts
Is a 240v input/220v 3ph output 2hp sensorless vector drive too big for a 1/2 hp 220v 3ph delta motor?
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23rd Jun 2015, 11:04 AM #2Member: Blue and white apron brigade
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23rd Jun 2015, 12:55 PM #3Cba
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When configuring, you simply tell the VFD that the motor is 1/2HP, and its nameplate current rating. The VFD will then properly protect your motor and limit its maximum current/power to it.
There can be one problem though. In operation the VFD calculates how hot the motor is at any given time. It does this by assuming the motor has the thermal characteristics of a standard TEFC motor. It then monitors its current, and calculates current x current x time (or I2t). That works fine, until you turn the VFD off and on again without pause. As you turn it on, the VFD processor will have forgotten the last I2t values and assume the motor is cold. This can lead to overheating of the motor, particularly if powered off/on several times in short sequence.
It is therefore recommended (particularly if the motor is smaller than the VFD) that the motor be fitted with either a cheap thermoswitch that inhibits the VFD if the motor gets too hot. Or the motor be fitted with a proper thermocouple that always tells the VFD the actual motor temperature.
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23rd Jun 2015, 04:27 PM #4Most Valued Member
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