3 Phase motor overspeed ?

[cuslog]

Further to my previous thread re: VFD suppliers, I have ordered a Hitachi WJ200 - should be here in the next few days.
Downloaded the manual and started studying it - wow, so many parameters to program !
Now, I'm wondering about over speeding the motor. It'll be driving a 2hp Baldor M3587T 3ph, 1740rpm motor.
I had never considered over speed as an option until I started reading the manual and VFDs in general.
I think 6 ~60 hz are the factory defaults but I think its possible to input up to 400hz as a maximum.
I'm relatively new to all of this and jumping it up to 400hz just seems like a bad idea to me but would it take 120 hz to effectively double the speed of the motor to ~3400 ? I mean, would the motor take it ? Depends, I suppose on the load and whether or not it would over heat ?
TIA

[rklopp]

120Hz should be fine, but there won't be much torque. It is likely the rotor in the 1740-RPM motor is the same as would be in a 3480-RPM version of the same motor.


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[MaxHeadRoom]

I usually do not run a standard 4 pole motor more than 120Hz, never had a problem.
MY logic is that the motor manuf probably makes 2 pole also so to the same standard of balance and bearings etc would be incorporated in the 4 pole version.
Max.

[DR]

Back in the day Baldor was a customer in their Sweo drive division. A Baldor engineer told me all newer Baldor motors are safely capable of 5,000 rpm.

I picked up a used Delta VFD that had been replaced under warranty on a Grizzly wood lathe. Their VFD's parameters are factory set at max of 120 hz and password protected for operator safety (they don't want anybody to jack the motor up to 400 hz). Other parameters are also protected such as those for remote potentiometer and start stop buttons. There's no easy way to decipher the password and unlock preset parameters so I had to build a remote panel with potentiometer and start stop buttons to use the VFD.

Not a bad idea to set the max hz of the VFD, otherwise you probably don't need to fool with other parameters.

[Peter.]

Think of all the small engines that happily run to 10k and more with unbalanced loads hanging off the bearings. 3k or even 5k would not tax a balanced motor assembly. My only fear would be for the cooling fan.

[epicfail48]

I recall reading somewhere a while back that most 3 phase motors are safe to run up to double speed at the price of reduced bearing like. I want to say it was some official document from a motor company, but devil if i know for sure. At any rate, id be comfortable pushing it up to 120hz, but not as a regular thing. If i needed a motor to spin 3500rpm, id much rather have a 3500rpm motor than push a 1750rpm one beyond its design

[CPeter]

When I converted my mill/drill to 3 phase and a VFD, I purchased a new 1725 motor from Automation Direct. It is rated for a maximum of 5,400 RPMs. I run it up to 4,000. Above the rated RPM, the HP is constant and the torque falls off so you don't get added power, just added speed.
CPeter

[alanganes]

I can't seem to find it right now, but I seem to recall that a member here actually did a test with an old 3Ph motor they didn't need and a VFD, running the frequency up to some fairly ridiculously high level just as a test to see what would happen to the motor. I believe they posted a video about it.

If I recall correctly, the end conclusion was that the motor didn't particularly mind, at least for the amount of time they ran it, as in no catastrophic failure of the armature, etc. It was quite interesting. Maybe they will chime in here or someone with more finely tuned search skills can find it.

[J Tiers]

It depends in part on the moor design type. Some have the "bars" on the OD of the rotor, some have them set "in" a bit, with the rotor steel partially holding them in. That construction affects the motor operation and starting current, but also can hold the bars in and allow a higher speed than a design with the bars exposed on the OD.

....

I picked up a used Delta VFD that had been replaced under warranty on a Grizzly wood lathe. Their VFD's parameters are factory set at max of 120 hz and password protected for operator safety (they don't want anybody to jack the motor up to 400 hz). Other parameters are also protected such as those for remote potentiometer and start stop buttons. There's no easy way to decipher the password and unlock preset parameters so I had to build a remote panel with potentiometer and start stop buttons to use the VFD.

....

Usually there is a way to reset to factory settings. That gets rid of the password, but you have to reset parameters to what you need.

[DR]

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Usually there is a way to reset to factory settings. That gets rid of the password, but you have to reset parameters to what you need.

Yes, there is a single parameter to reset everything to the factory defaults, but being password protected that parameter couldn't be enabled. Per the online instruction manual the only way to override the password was by hooking a PC to the VFD through a special connection protocol.

It was interesting to note that Grizzly's service folks don't have knowledge or capability to service the VFD's, they simply replace them if there are any problems related to motor control. In this case the problem was dust in the remote lathe spindle speed indicator pickup.

It's not so much that motors can safely be over speeded, but the danger is in what the motor is driving.

[cuslog]

Thanks for your replies guys.
Thought about it some more after my original post and I think what I'll do is initially start out conservative, like maybe 70 or 80 hz, see how it reacts, if that seems OK, then try bumping it up. Probably be OK with lower torque because there's a 15:1 gearbox between the motor and the drive screw.

[MaxHeadRoom]

A Baldor engineer told me all newer Baldor motors are safely capable of 5,000 rpm.

.

Traditionally Baldor has listed them as 'Vector Rated' motors.
Max.

[Peter.]

I can't seem to find it right now, but I seem to recall that a member here actually did a test with an old 3Ph motor they didn't need and a VFD, running the frequency up to some fairly ridiculously high level just as a test to see what would happen to the motor. I believe they posted a video about it.

If I recall correctly, the end conclusion was that the motor didn't particularly mind, at least for the amount of time they ran it, as in no catastrophic failure of the armature, etc. It was quite interesting. Maybe they will chime in here or someone with more finely tuned search skills can find it.

Wasn't that John Stevenson? Mounted a collet chuck directly to a motor spindle?

[Peter.]

Took some time but I found it:

http://bbs.homeshopmachinist.net/threads/19653-Gotta-new-toy?p=233294#post233294

[DR]

Underspeeding of motors too?? Years ago on another forum a member told about setting up flux vector VFD's to use motors for a low speed positioning application. The motors had encoders mounted to monitor their exact shaft orientation which was fed back to a PC which used the VFD to control the rotation. The application was similar to the way servo motors act on CNC machines. Note: this is not the same as sensorless flux drives you see advertised.