What the heck?

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fabricator

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I got a cheap VFD from amazon and hooked it up to a new to me Harig surface grinder with a Leeson 3HP motor. The results were something I've never seen before, it sounds just like the motor is spinning up but the shaft isn't turning. That is a weird one, this is a relatively new brushless motor. So I found a different 2hp 3 phase motor and hooked it up and it spins up just fine. The Leeson sounds like there is a motor inside spinning up, it's wired for 220 right off the name tag. Can it be some kind of weird magnetic flux thing causing it to sound like that? I'm probably going to use the 2hp motor but I'm really curious as to what the problem might be.
 

RM-MN

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Wild guess! The armature is probably pressed onto the shaft with no other fastener. It might be spinning the armature on the shaft.
 

fabricator

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Wild guesses aren't wild in this situation:) I checked that yesterday and it's solidly attached to the shaft. Thanks for the comment though.
 

EMF

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If its a brushless motor, you can't drive it with regular VFD, you need the electronics to drive it. Google brushless motors and get a feel for the requirements. Your equipment probably had the driver in a separate box where the switching was and you didn't get that part.
 

fabricator

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I put the same vfd on a different 220v AC brushless induction motor and it works fine.
 

David Shealey

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You may be confusing "Brushless" motors with AC induction motors! Sure, AC induction motors have no brushes, but the term Brushless is relative to DC motors that do not have brushes. Those have electronic commutation instead of brushes. Was there a speed controller of some sort on the machine? You are putting this on a Surface Grinder? Speed control on a grinder spindle is new to me. What is the purpose?
 

fabricator

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You are right, they are ac induction motors. The VFD is not for speed control at all, I have a lot of 3 phase motors and this is a less expensive alternative to buying a new or used single phase 3hp C face motor.
 

David Shealey

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I thought of the use for 3 Phase right after I posted. I had looked at VFD for my Bridgeport, but I bought a 5 HP rotary phase converter for it, with the thought of changing the single phase motor on my 13X40 lathe. Have not done that yet, but occasionally looking at possible motors to do it.
 

fabricator

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I have VFD's on my lathe and mill, speed control is absolutely limitless and you can set up instant forward and reverse for things like tapping holes. My
 

awake

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Not meant in an argumentative way, but just to add information: my BP has fully variable speed control within its appropriate working range (no, you can't spin the spindle up to 30K!), and it can instantly reverse for tapping, but no VFD - just the basic 2J varispeed head, 3-phase motor running on a rotary converter.

Again, I am not knocking the advantages of a VFD, but just noting that, for some machines, a VFD may not add as much advantage as it would for others (e.g., for a BP or lathe where you have to change the belts to different pulleys).

Also, rotary converters can have potential advantages over VFD's. One is that, if one happens to have access to scrap motors and parts, it can cost nearly nothing to make an RC. The other is that, on some machines, using a VFD means not using the built-in controls or features, especially those that run on separate motors. That latter is what I have read, not from personal experience, so take it with a grain of salt.
 

SailplaneDriver

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Single phasing a three phase motor will cause it to hum like you are describing. The problem is between the motor and the VFD if you got another motor to run. Check your connections to make sure you did not inadvertantly leave one phase open. Check the wiring diagram of the motor (if there is one - usually on the nameplate). Make sure the motor is connected correctly for the voltage and that the neutral connection (if any) is wired with the proper polarity. I can describe a test you can perform if the leads are not marked for polarity. Check the motor windings to see if any are open circuited. The method will depend upon the number of leads the motor has.
 

fabricator

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So I just got a new VFD from automation direct and Hooked it up to the motor in question and it runs perfectly. I hooked the cheap amazon VFD back up to it and it makes the same noises and the shaft doesn't spin. I then hooked it up to the 2hp motor and just like before it spins that one. The GS2 drive from automation direct spins both motors. I have to conclude what I knew all along, you get what you pay for, the Automation Direct VFD comes with an easy to follow manual that was written by a native English speaker also. The unit is much heavier and of very obviously much higher quality for just $150 bux more.
 

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