VFD Speed Question

I currently hooked up a Power Flex 4 to one of our machines. In order for us to get the feet per minute with our drive we have to run the motor at 100Hz........Now I can changed the FPM of the belt by changing the drive sprocket, but is this needed? Does running a drive faster do any harm to an AC Motor? Would are some opinions? Changed the drive sprocket or run motor at higher HZ through VFD? Thanks

As long as:

A. You don't need high amounts of torque
B. The motot bearings will handle it

You will be aok.
If it were me, and it weren't too much trouble, I'd change the drive sprocket anyhow.

In general, you can run a suited motor (any decent motor) at 200% of rated speed. You are in the US, so that would be at 120 Hz.

While it is always best to run the motor as close to rated speed as possible, there generally isn't much of a problem running at 200%.

However, judgements are best made if you understand the particular loading and torque requirements.

As long as the motor is nameplated 1800rpm or less, going to 100Hz is probably a good idea. Being a PLC4, the hp is low so, if I were designing a new system like yours, I'd probably choose a sprocket so the motor went to 90Hz.

Bottom line: leave it the way it is. You are getting better speed regulation, higher starting torque, and better motor cooling as a result. And, don't worry about the bearings--they use the same bearings in a 2-pole motor to run at 3600rpm.

I have a 'Team Leader' who argues any motor driven over nameplate frequency (60 hz) is bad practice, harmful to the motor, blah, blah, blah..
I have seen many cases where mechanical changes were made to pulleys and gearboxes where an increase to even 70 hz was required.
Can anyone give me an authoritative source to help prove to this neanderthal that overspeeding a motor, especially an inverter rated motor is OK. If I tell him DickDV says its OK he'll go off his rocker again!

Thanks,

Brian.

Easy. If the motor is inverter rated to 3600 RPMs, the drive is rated to 400 Hz r whatever, and you drive the motor at 2000 RPMs and the drive at 75 Hz, you're well under manufacturer's ratings for the systems.

Yah! Sliver! Just the mention of my name often makes people go off their rocker. I've noticed that with some chagrin!! Haven't been able to stop it however! Frustrating!

Seriously, tho, simply obtain a hard copy or download a standard Reliance Electric Motor catalog. It doesn't have to be an Inverter Motor catalog, just a commodity motor catalog will do.

Take a look at the torque-speed curves in the front of the book (at least they used to be when I was working for one of their distributors). You will see that even the commodity TEFC motors are shown to have acceptable operating ranges often to 90Hz, a bit less as the hp goes up over 50 or so.

If the mfgr says its ok, that's good enough for me and should be good enough for most neanderthals too.

And, the best part is that my name doesn't show up anywhere!!!

Good luck!

We had an issue where a machine would trip the drive off after the drive was about a year old. Change the drive and good for another year.

We finally really looked at the system after 2 drives and found that when the machine was set to its fastest speed the drive was running at about 160 hz.

The operators normally run at the fastest speed. I believe it was about a 2.5 - 3hp motor with a 1336 drive I believe.

We ordered a new pulley for the motor to bring full speed of the drive down to 70 -80 hz and its been running solid for well over 3 years now.

In short the system will not have an issue running there but longevity might be sacrificed. I have seen other types of machines with no issues running at the same hz.

Drewcrew6

Dick,

In your opinion, assuming a motor is controlled by a ramping 4-20 mA signal, if a motor is lightly, or at least reasonably, loaded, under all conditions, would running at 200% (120 Hz) be acceptable?

Why, or why not?