Can you get your hands on the T&B reports to find out what cfm you should be moving with that fan and the others that you are having trouble with? If so I would go that route.. If its not a voltage or a mechanical issue, I would be inclined to think that it is an airflow issue.. Good luck buddy. Let us know what you come up with..
A fan motor that is pulling excessive amps is either defective or doing more work than it was designed to do. You have 99.9% eliminated the first possibility by replacing the motor. If this is a long established system and the problem is just-now-new - then something has changed in the system to reduce resistance to air flow.
So, as I see it the options are these:
1. The best method is reduce the blower speed by adjusting the drive sheave to a smaller effective diameter until the amp draw matches the FLA / RLA listed on the motor's name plate.
2. The other way is to reduce the max allowable amps / motor speed by altering the freak drive's parameters.
3. Find out why and how the air system has changed in a way which has resulted in a lesser resistance to air flow.
What do you mean: "return fan motor" ? Is this a push/pull system in a large air handler or packaged unit?
Originally Posted by Onefast450r
Ive got a 1.5 hp 1750 rpm 460 volt return fan motor that has been giving me issues overamping for the last 2 months. The freq drive is tripping on calculated motor temp. Basically it monitors the motors amperage and bases that on motor temperature. The nameplate states that at 460 volt the motor should pull 2.2 amps. The motor is pulling 3 to 3.5 amps. I replaced it with a weg motor with the same nameplate data. New motor is doing the same thing. Ive checked all my connections, looked at the contacts on the contactor. Everything looks good. I even bypassed the drive itself by running temporary wires directly from the disconnect to the motor. Same problem. The fan spins freely, as free as the identical one located in the same mech room which is running normal at 1.8 amps. The belt is snug like it should be. Remove the belt and the motor pulls .8 amps. My voltage looks good at 492 across all three legs. Something has changed in the last 2 months that is now causing this problem. Any ideas?
The conventional view serves to protect us from the painful job of thinking.