VFD Help

[lanternnate]

I’m finally getting around to trying to wire up my little disc grinder build. Just a little 1/2 hp 220v 3ph and a KBWA VFD. I’ve got it all wired up, but it doesn’t want to start on it’s own. I turn it on, then set to FWD, then turn the speed dial up a bit. It makes noise but no movement. Just the slightest “jump start” of spinning the shaft with my fingers and it starts spinning away and running just fine. The speed ramps up and down seemingly fine with the dial once it’s going. I can flip it to reverse and it spins the alternate direction, but again requires that little manual spin to get going. I’m assuming I have something incorrectly set in the VFD. I have installed the connector to make the VFD 115v in. The hz jumpers are set to 60hz and 1x. I’m assuming the wiring itself is correct because it does run and will go forward and reverse. Could this behavior be a trim pot setting? I have the following pots available to adjust: minimum speed, maximum speed, acceleration, deceleration, slip compensation, current limit. I set these all to what appeared to be “default” on the quick start instructions. There is also a start mode jumper that has an automatic or manual option. I currently have that jumper installed for “automatic” because that was the factory setting. Any thoughts on what I might have wrong?

 

[lanternnate]

So very odd. Fiddling around some more, I set it to FWD but intentionally spun it backwards to see what would happen. It actually started running under power in the reverse direction for a while. Then something “caught” and it started spinning under power the correct direction. Now it magically starts and stops all on its own just like it should. I’m not sure if I should be happy that I somehow dumb luck stumbled into fixing it or if I should be worried about something being potentially loose or wrong in the motor that might come back to haunt me.

 

[Drew Riley]

What kind of motor is it? Can you provide a pic of the nameplate? Are you sure it's wired for 220VAC?

With the motor disconnected, do you get the same (or close) ohm readings between the windings? (L1 to L2, L2 to L3, L1 to L3)

Sound like you may be missing a phase... Are you sure all of your connections are right and tight?

 

[lanternnate]

Sound like you may be missing a phase... Are you sure all of your connections are right and tight?

This ended up being it. Just after my last post where I said it was good, I turned it on again and back to the same problem. A cable jiggle changed the behavior again though, so doh! Unplugged and popped the cover on the motor, sure enough the wire nut on the T2-T8-L2 connection was loose. Tightened that up and everything is happy, yup I’m an idiot. I don’t quite understand 3ph. I incorrectly assumed I wouldn’t be running at all if one of the phases came unhooked.

 

[Drew Riley]

Glad you figured it out and that it was something simple. You're partly right in thinking it shouldn't run (or at least shouldn't start) with a dropped phase (hence why you had to start it by hand). This is more/less the principle that static phase converters are based off of, starting the motor "artificially", and then allowing it to run without all three phases. They can technically run this way, but the motor will be derated, and ultimately it's not that great for the motor.