3 phase motor runs slow.

[janc]

I have a 3 phase motor that runs very slow, maybe 200 rpm, it's new to me and it's my first time using a VFD, all my other 3 phase equipment is run on a rotary converter, but thought I would try a VFD for a variety of reasons.
I tested the VFD on another motor and it works as it should, the slow motor runs smooth and quiet, it reverses, no response when changing the frequency, no smoke, buzzing, or heating, and it's wired for the correct voltage.
Any ideas what I should check?

 

[richard newman]

Did you try running the motor on your rotary phase converter?

 

[Joe Gwinn]

I have a 3 phase motor that runs very slow, maybe 200 rpm, it's new to me and it's my first time using a VFD, all my other 3 phase equipment is run on a rotary converter, but thought I would try a VFD for a variety of reasons.
I tested the VFD on another motor and it works as it should, the slow motor runs smooth and quiet, it reverses, no response when changing the frequency, no smoke, buzzing, or heating, and it's wired for the correct voltage.
Any ideas what I should check?

I assume that the rotor turns freely by hand when not under power.

One of the three phases may be open, perhaps within the motor. Use an ohmmeter to tell.

 

[Clive603]

Check the parameter settings on the VFD.

Most VFD boxes have an internal maximum speed setting that over-rides the controls to guard against dangerous fiddling. Usually takes a bit of finding in the manual, normally disabled on a new VFD. Usually the display stalls when the preset speed is reached but some VFD boxes let you set the desired speed but need an extra button push before they will follow the setting. I have one that is seriously confusing in operation due to this feature being badly implemented.

Also check current limits in particular. Especially if its a plain voltage / frequency device rather than a more modern vector drive. Its possible to set up an old style VFD in such a manner that it won't deliver enough current to run-up a motor even off load. Usually you only hit that problem when driving a significant load such as a compressor where extra boost current may be needed to get it over then current demand hump around half speed.

Self tuning vector drive usually have a current boost setting to overcome this. I put one on a Hydrovane compressor that round settle rock steady at half speed if the boost setting was not enabled!

Clive

 

[Vcmt]

Is the motor wired for 440 volts

 

[janc]

Tested the motor on the rotary power source and it works fine, there are no faults evident when checking the motor with a meter, the motor is wired 220v, and the VFD is 220v, the VFD is new, and as stated earlier, the VFD worked fine on a new ABB 3 phase motor, there is no load on the motor when testing.

 

[Joe Gwinn]

Tested the motor on the rotary power source and it works fine, there are no faults evident when checking the motor with a meter, the motor is wired 220v, and the VFD is 220v, the VFD is new, and as stated earlier, the VFD worked fine on a new ABB 3 phase motor, there is no load on the motor when testing.

Is there electrical continuity on all three leads measured two at a time?

 

[eKretz]

What does the current draw look like on the RPC vs on the VFD? Check all the legs. I'm assuming the motor looks fine when checked for resistance with a meter between individual leads and between each lead to frame, since he already said so...

 

[janc]

Is there electrical continuity on all three leads measured two at a time?

Yes.

When testing the voltage on the VFD while the motor was running this is what I got;
Input, 240v
Output, from ground to each leg 240V, 240V, 350V from leg to leg, 35v to 50V jumping around, 340V, and 100V.

 

[janc]

Switched around the output wires on VFD and got it to work, I think, speed control works, and motor speed is better, but still seems slower than with the rotary, will have to check that out more tomorrow, output voltages from the VFD are stable now, but still not what I would expect, should that be checked under load?

 

[rons]

Run the VFD auto tune function. If the motor spins faster than you have seen before then you are onto something.

You measure voltages from phase to phase, not phase to ground.

What VFD? ( here it comes)

 

[janc]

It's a cheap China VFD, Vevor brand, some of their stuff is pretty good, deciphering the instructions is a challenge, can always send it back if it don't work.

 

[eKretz]

It's hard to check phase/phase voltage accurately when you're running a VFD unless you have a meter with a low pass filter (or something with slow response like an analog needle) because of the pulsed output. Easier to use a current clamp.

 

[janc]

After getting it to make the motor run at some speed, go faster or slower, and reverse, the motor has almost zero power, (full power on the rotary) and have gone over the wiring and all the parameters many times, also the power requirements for the motor are much lower than what the VFD should supply, I am ready to throw in the towel and send it back.

 

[EmGo]

It's hard to check phase/phase voltage accurately when you're running a VFD unless you have a meter with a low pass filter (or something with slow response like an analog needle) because of the pulsed output. Easier to use a current clamp.

I swear, for a shop with cnc machines, a scope is well worth the cost. So many things you can see on even a cheap 20 mhz clunker that are invisible even with a good vom.

 

[eKretz]

I swear, for a shop with cnc machines, a scope is well worth the cost. So many things you can see on even a cheap 20 mhz clunker that are invisible even with a good vom.

Yep. I have several floating around. Including a portable with fully isolated inputs/grounds. Very handy indeed.

 

[eKretz]

After getting it to make the motor run at some speed, go faster or slower, and reverse, the motor has almost zero power, (full power on the rotary) and have gone over the wiring and all the parameters many times, also the power requirements for the motor are much lower than what the VFD should supply, I am ready to throw in the towel and send it back.

I don't trust those cheap import VFDs, but I'm not sure why it would work fine with one motor and not another unless you have some sort of leakage current that you aren't detecting.

I have a Hitachi 3 HP, a couple Yaskawa 5 HP, a Baldor 25 HP and a buddy of mine uses about 5 Invertek from 2-5 HP with no complaints. They aren't really that expensive these days.

 

[janc]

I don't trust those cheap import VFDs, but I'm not sure why it would work fine with one motor and not another unless you have some sort of leakage current that you aren't detecting.

I retested the new ABB motor on the VFD and rotary, on the VFD ok speed but very little power, rotary produced both good speed and power.

 

[eKretz]

I don't trust those cheap import VFDs, but I'm not sure why it would work fine with one motor and not another unless you have some sort of leakage current that you aren't detecting.

I retested the new ABB motor on the VFD and rotary, on the VFD ok speed but very little power, rotary produced both good speed and power.

Sounds like your cheap VFD is no good. There's a reason they are verboten for discussion here

 

[janc]

Sounds like your cheap VFD is no good. There's a reason they are verboten for discussion here

I can see why they are banned, trying to figure out this POS VFD is a waste of everybody's time, sorry, but I did learn a good lesson on China electronics, thought I could use this as a cheap way to learn about VFD's, not.

Thanks for trying to help.