Drives and motors won’t last forever. They operate in harsh environments and are expected to meet tough demands. Eventually, you’ll run into a scenario when one of these critical machines does not function properly. Assuming your motor is in top shape, it may be time to consider whether or not your drive is faulty.
While it is possible that drive has a critical error, there are several issues you should troubleshoot before coming to that conclusion.
– Make sure the drive is actually receiving power. After confirming that your equipment is properly connected, the best way to test your drive’s power supply is measuring the supply voltage. Do this as close as possible to the drive, ideally right next to the power input terminals (the ABB ACS550’s power input terminals are labeled U1, V1 and W1, for example).
– Make sure any device externally connected to the drive isn’t at fault. This is really only necessary if the motor leads are not directly connected to the drive’s terminals. Most DC motors have an armature resistance that is very low (often one ohm or less), so external resistance must be placed in series with the motor to keep the starting current in check. If you measure low resistance at the drive, the problem is likely within this series (relays, plugs, connectors, etc.).
– Check to see that the drive is receiving the command signal required to make the motor run. If you’re using a speed potentiometer, measure across the command or communications terminal on your drive (labeled X1 on the ABB ACS550 drive, for example) to determine whether there are linear increases or decreases in the command signal as you alter the position of the potentiometer. If an external command is being provided, check to see if it varies in the way that you expect.
– Double check inhibit/enable commands. Some applications make use of these commands to stop a motor as quickly as possible while leaving the drive powered. You will want to use the enable to command so the drive will output motor voltage.
– Adjustments to the drive can result in a “missing” motor voltage. If the current limit is set too low, the motor will stall as soon as it demands current. It is fairly common to set the current limit higher than the rated current for testing purposes.