WEG CFW300/320 VFD Over Current Debug Part I from AutomationDirect

There’s a couple things that can cause an overcurrent fault. The most common cause is wiring. Either two or more motor phases are shorted together, or a motor phase is shorted to ground. For example, If I hit run the drive spins the motor up to speed just fine. But, if I use a clip lead to short two of the motor phases … and then hit run, the drive sees the issue, immediately shuts down the output to prevent damage to the system and issues a overcurrent fault code. Remove the jumper, reset the fault, hit run, and we are back to normal. So, if you get an overcurrent fault, check your motor’s wiring. The quickest way to do that is with the drive powered down of course - remove the motor’s wiring from the drive and then hit RUN. If the drive runs without a fault, then there is definitely something wrong with the wiring to the motor or the motor has an internal short. If you still get the fault code with no motor connected, then there could be an issue with the drive. Try removing any braking resistor you may have, resetting the drive to factory default, and re-entering your basic motor parameters. Often that will get the drive running, and then you can slowly add the other parameters you changed back in until you find the one causing the issue. If the drive still doesn’t run after all of that, try swapping it out with a known good drive. Another possible reason for an overcurrent fault is the built in current limit function has been turned off. The WEG CFW300 Drive has current limiting built in so normally if you specify an acceleration ramp that is too short, the drive will automatically change the ramp time to prevent an overcurrent fault. But, if you turn that current limiting function off and enter a really short acceleration time you will get an over current fault. Let’s try it. I’ll go to the current limiting threshold in parameter 135 and set it to a big number and that will disable current limiting. If we go to parameter 100 we see we still have a really short acceleration tie, so that’s fine. So I’ll hit RUN, and we immediately get an overcurrent fault. If I clear the fault, and then extend the ramp time to something reasonable, say 5 seconds, and then hit run … everything works great. So, if you’re getting an overcurrent fault under load, then make sure the Current Limiting Threshold is set to an appropriate value and the acceleration time is reasonable. The way that the WEG CFW300 handles current limiting and current regulation in general is really good stuff to understand, and will help you set that current limiting threshold appropriately. But, it’s large topic all by itself, so we’ll cover that in part II. Click here to learn more about the WEG CFW300 Variable Frequency Drive. Click here to learn about AutomationDirect’s free award-winning support options and click here to subscribe to our YouTube channel so you will be notified when we publish new videos.