Thread: VFD struggling to power on motor

[Dan1900]

I recently hooked up a new Fuji frenic mini VFD to an older 3/4hp motor on my SB Heavy 10. I input all the needed motor parameters and functions into the vfd but I am having a strange recurring issue. The first time I power on the VFD, it works fine. Then when I power it off, sometimes but not always, it will lock up the motor. I go to start the motor again and it sounds like the vfd is trying to get the motor to start but just can't. When this happens, I have to go over and tug on the pulleys to get the motor shaft to move and this slowly unblocks the motor.

Again this doesnt happen every time but still maybe 50% of the time. I thought I would bump the torque boost on the vfd to +20% and it still locks up on 2nd startup. I changed the parameters so it doesn't decelerate the motor so quick (I had it set to 1.5 or 2 seconds acceleration / deceleration).

Any one have any ideas what might be the issue?

 

[WJ Birmingham]

Sounds like the VFD or the motor is dropping a leg out of the loop.

I've never used Fuji VFDs... I like the Automation Direct stuff because of the awesome support they have, when I've needed it.

 

[Dan1900]

Sounds like the VFD or the motor is dropping a leg out of the loop.

I've never used Fuji VFDs... I like the Automation Direct stuff because of the awesome support they have, when I've needed it.

I am not sure exactly what you mean by dropping a leg out of the loop.

I will add another detail though, when the motor is not tensioned by the belt, it seems to have less issues starting up. As soon as I add the belt to hook it up to the countershaft, that's when the issue starts happening. And the belt has been tensioned properly, even a little on the light side to see if that might have been the issue.

 

[Dobermann]

Try setting the motor deceleration to "coast to stop" or something similar. I'm not sure what actual term TECO uses. But rather than trying to force a time to stop which could involve application of a DC voltage to the motor windings to force braking, just let it stop by itself and see if that helps.

 

[jmm03]

Will this occur if you do not have the motor connected to the lathe? Possibly a bearing problem that occurs after running for awhile and the bearings heat up,closing up the tolerances. Jim

 

[WJ Birmingham]

I am not sure exactly what you mean by dropping a leg out of the loop.

I will add another detail though, when the motor is not tensioned by the belt, it seems to have less issues starting up. As soon as I add the belt to hook it up to the countershaft, that's when the issue starts happening. And the belt has been tensioned properly, even a little on the light side to see if that might have been the issue.

It's 3 phase. It has 3 legs. If a leg drops out, you lose a significant amount of power and RPM. If you let it go long enough, you'll probably start seeing smoke rolling off the windings.

 

[iwananew10K]

try removing ALL other loads on the circuit...115v is pretty well taxed even at 3/4HP if other loads are on the same circuit.

 

[Dan1900]

So if a leg has indeed dropped out, is that a wiring issue or something mechanically wrong with the motor? It is a pretty old motor so maybe it's just on it's last legs? Is there a way to diagnose this? Electronics are not my speciality.

Thanks

It's 3 phase. It has 3 legs. If a leg drops out, you lose a significant amount of power and RPM. If you let it go long enough, you'll probably start seeing smoke rolling off the windings.

 

[WJ Birmingham]

So if a leg has indeed dropped out, is that a wiring issue or something mechanically wrong with the motor? It is a pretty old motor so maybe it's just on it's last legs? Is there a way to diagnose this? Electronics are not my speciality.

Thanks

Could be the VFD, could be the motor, could be the wiring.

 

[DanMc77]

Use an ohm meter to measure the resistance across each of the 3 windings in the motor. They should all measure about the same.

 

[Cole2534]

Use an ohm meter to measure the resistance across each of the 3 windings in the motor. They should all measure about the same.

And then measure them to ground, where you should get 0.

 

[rock1455]

I had a very similar situation and I had overlooked the voltage wiring at the motor and assumed it was set for 220 V. It was still configured for 480 volts.
Once I reconfigured it for 220, it worked great with no additional changes on the VFD.
Pay very close attention to the diagram on the motor for the correct wiring.

It does sound like you were previously using this lathe so the voltage configuration should be correct if you were using 220V input previously, but thought I would just mention anyway, it is a quick check.
Good luck

 

[hsracer201]

I looked up the micro and there appear to be different configurations available. Is this a single phase 110v in and 220v 3-phase out? I had one of those one time and it just wouldn't cut it, it did what yours is doing. I moved up to a 220v input and it worked as it should.

 

[Toms Wheels]

First I'd look at the wiring, if the motor is "Locked" th at would indicate power to the windings, but not all three sets. As opposed To a free turning by hand condition. Correct?

I assume you are using keypad, or remote mounted switches to control the motor, NOT powering on or off the VFD or using the SB motor control. Is that correct?

What is the Acc time set at, what is the min frequency set to?

Be sure motor is wired for 220V, not 110v.

 

[Dan1900]

You are correct, it is 110v in with 220v 3 phase out. Unfortunately that's all I have access to at the moment until I move in a few months. I also have a wood lathe running on 110v but that's using a DC controller/motor so different story.

As an aside, I think I bought a heavy 10 steady off you on ebay last week.

I looked up the micro and there appear to be different configurations available. Is this a single phase 110v in and 220v 3-phase out? I had one of those one time and it just wouldn't cut it, it did what yours is doing. I moved up to a 220v input and it worked as it should.

 

[awander]

And then measure them to ground, where you should get 0.

Surely you should read infinite ohms or overload from the windings to ground?

 

[GenePoole]

Surely you should read infinite ohms or overload from the windings to ground?

You'll need a "megger" to properly check the windings resistance to ground.

 

[awander]

You'll need a "megger" to properly check the windings resistance to ground.

If an ohmmeter reads "zero", then you don't really need a megger...

 

[gadget73]

any phase to ground should read infinite ohms. Properly done with a megger but an ohm meter will tell if its a dead short. If its not blowing breakers or tripping the VFD, you probably don't have a case to ground short.

Sounds like the VFD is braking, not just letting the motor coast down. Check your settings and make sure its not set to brake and hold or whatever options it may have. If there are any low rpm torque boost options, maybe check those settings out too. If you've got a link to the manual for the VFD you have, post it and maybe someone can make specific suggestions.

also if this is a used unit, reset it to defaults, then input your motor data. It may have some weird configuration in the obscure settings.

 

[Dan1900]

It is a Fuji FRN0005C2S-6U. Here is a link to the manual. Another thread I started suggested the FLA not being set correctly could have caused this issue. I will also look in to what you mentioned with the control mode.

https://americas.fujielectric.com/files/SI47-1839-E.PDF

any phase to ground should read infinite ohms. Properly done with a megger but an ohm meter will tell if its a dead short. If its not blowing breakers or tripping the VFD, you probably don't have a case to ground short.

Sounds like the VFD is braking, not just letting the motor coast down. Check your settings and make sure its not set to brake and hold or whatever options it may have. If there are any low rpm torque boost options, maybe check those settings out too. If you've got a link to the manual for the VFD you have, post it and maybe someone can make specific suggestions.

also if this is a used unit, reset it to defaults, then input your motor data. It may have some weird configuration in the obscure settings.