Fans, Blowers & Motors
I am installing a Variable Frequency Drive (VFD) for the unload system. Is there anything I should know?
The variable frequency drive (VFD) is a good method of protecting the motor and changing speeds of a motor. The VFD changes hertz from 5-72 or anywhere in-between. The more hertz applied the faster the motor runs in RPMs. The downside to the VFD is that it emits noise and signal wiring can pick up noise and vary signals.
- Make sure all signal cables are grounded well on one end.
- Make sure wires for the low voltage and signal are not anywhere close to the VFD.
- The VFD motor output wires should not be close to the 120 VAC control wires.
- If motor coupling (sure-flex sleeve) has gone bad or been damaged while running for a short time frame, then the motor shaft and fan shaft are not properly aligned. The alignment is what the flex sleeve will help with, but when alignment is too far out of tolerance then the coupling will become damaged.
- This could also be because flanges that hold coupling are too tight or too loose. The coupling needs to fit snug in place between two flanges.
- Incorrect size coupling and flanges were used for the application.
First, take a straight edge and place it across the top of both pulleys to ensure proper alignment. The best way to check tension is to own a belt tension tool along with a belt tension guide. These are available at order houses such as Grainger or houses that specialize in bearings and belts like Standard Bearings. A good automotive store might also have them on hand or be able to order them for you.
If a centrifugal fan belts are loose, they will not always emit the typical loose belt squeal. On start up, especially on a dryer with a soft starter, you will hear the RPMs vary instead of hearing a smooth ramp up of RPMs. With a tri-start system, the sound might sound like a distant jet engine as each motor comes up to full speed. Another indicator of loose belts is decreased capacity.
- The LP or Natural gas fuel supply does not have enough supply to increase temperatures past a given point, contact the utility company.
- Modulating valves will not adjust temperature to give proper increase in chamber temperature. Remove bulb from heat and put into ice or a cool place and restart the burner. The burner should go to maximum output and trip off high limits if you do not control temperature with hand valve. If temperature does not go to maximum and stays where it was before exposing bulb to cold temperatures, then power element is bad and must be replaced.
- Proportional valve may not be opening to allow more fuel to burner. Proportional valve has a clear cover and slot cut into shaft. Actuator is orange Belimo valve and will rotate slot from shut position, slot is 90-degrees from pipe train. In the open position, slot is in line with pipe train. This is controlled by 0-10 DCV signal and 24 DCV to run motor, check Belimo for voltage. 1 to 2 is 24 DCV and 1 to 3 is 0-10 DCV at the Belimo actuator.
- Check gas pressure gauges for pressure while running burner, loss in pressure can result in a loss in chamber temperature. If gauges are not properly working they need to be replaced.
- If no pressure is shown on gauges, check solenoids for opening. 120 volts to a solenoid should open coil and diaphragm.
- If solenoids are opening and no pressure is indicated on the gages, check hand valves for open position and check LP strain filter to see if it is plugged.
- If burner is operating and flame looks small, check air inlets and/or burner orifice for obstructions. Maxon burner holes could be corroded and need to be opened up with drill bit.
- Disconnect is not energized.
- Manual motor protector breaker is not turned on.
- No power to stop and start switch.
- Check for proper voltage across lines and line to ground.
- Motor is bad, replace motor. Motor leads can be checked for continuity using voltage meter and trained electrician.
- Motor rotor has seized and motor is in locked rotor condition, this will generate very large amp draw and hold amp draw until breaker trips. Replace motor or have motor re-worked by motor shop.
- Check for proper line voltages on all three legs.
- Check for proper belt tension.
- Investigate for worn bearings on both fan and motor.
- Try opening or closing louvers on the air doors.
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