What the heck?

[fabricator]

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]

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

 

[fabricator]

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]

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]

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

 

[David Shealey]

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]

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]

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]

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]

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]

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]

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.

 

[toadboy65]

I had a similar experience. I finished overhauling my new (to me) mill, hooked up a chinesium VFD, and had the same hum. I tried running wires from the good Hitachi VFD on my lathe to the mill motor, and it worked great.
I ended up rigging a switch to a couple of magnetic relays to let me choose one or the other machine. The Hitachi has a remote pad, which I can reach from either machine.
Anyway, I think the cheap VFDs just don't have the capacity of the better and heavier units.

 

[skyline1]

Having checked the connections and the motor windings as previously mentioned you could try starting the motor "off load" i.e. physically disconnected from the machine.

It sounds like the VFD cannot produce enough current to start the machine. If the motor spins up off load then this is most likely the case.

This is caused by one of 3 things.

1. The drive is simply not powerful enough, most of these cheaper Chinese devices are vastly exaggerated in terms of power output. I recently saw a Chinese Wind Generator with a claimed output of 3KW when it's actual output was only about 100 Watts. There are many other examples of this bad practice.

2. The drive is simply defective Chinese quality control is pretty lax at best and sometimes non existent.

3. The starting current is set too low. On many VFDs, especially the more expensive ones parameters like this can be adjusted to suit the motor and conditions.
However with a single sheet "chinglish manual" usually in very small print it is difficult if not impossible to work out how to do this. Especially if your knowledge of power electronics is limited.

If you could post a copy of any intructions you have with it or at least the model No this would help.

This may sound like I'm knocking Chinese equipment but I'm not, I have many pieces of Chinese gear that perform splendidly and were remarkably inexpensive.

In fact IMO some of their high end stuff is better than It's American or European rivals and usually considerably cheaper.

You do need to do some research though and read the specifications very carefully.

User reviews can also help you avoid some real "lemons" and Chinese Warranties are not usually reliable (although I have experienced exceptions)

Best Regards Mark

 

[fabricator]

I had a similar experience. I finished overhauling my new (to me) mill, hooked up a chinesium VFD, and had the same hum. I tried running wires from the good Hitachi VFD on my lathe to the mill motor, and it worked great.
I ended up rigging a switch to a couple of magnetic relays to let me choose one or the other machine. The Hitachi has a remote pad, which I can reach from either machine.
Anyway, I think the cheap VFDs just don't have the capacity of the better and heavier units.

That is exactly what I found to be the problem, I ended up ordering a GS2 drive from automation direct and it runs perfectly. Automation directs drives are very reasonably priced and the quality is many times better than the run of the mill Chinese junk from ebay or amazon and you get 24/7 American support and instruction manuals in actual English.

 

[Steamchick]

Hi all, Just spotted this thread, and haven't really studied what it is all about - and it sounds like "the horse has bolted" so please excuse me while I "shut the stable door". Putting it simply, a 2HP motor will give 2HP at optimum load/torque/speed: If driving (say) a lathe through lots of speed reduction pulleys, then you get the Mechanical advantage of the pulleys to increase the torque - but not the power - at the spindle. Which is great for machining! Or you can use the pulleys for higher speed than the motor, but the torque (not the power) at the spindle will reduce accordingly.
Then again, a Variable Speed Drive is current limited - usually designed so max. power rating is at "Optimum" speed.... not necessarily maximum speed, but it may be. So when you fit a VFD speed control to your lathe (or whatever) and try and take a decent cut at a very low speed - or in your case just overcome the starting friction of the 3HP motor? - the VFD will give it's rated current to the motor, but as the power is speed dependant there will be hardly anything coming out of the shaft.... The torque is constant on this VFD set-up, irrespective of speed - as it is current limited. But the power is gnat's elbow at start going up to the rating at the rated speed. Your simple solution (as I read what you have done already?) is to buy a bigger VFD, that gives more current to overcome the initial starting friction. Then it will give you whatever it can at whatever speed you use it at.
Example: My 1.5kW motor on my lathe will stall when tapping anything over 3/8" when at 80 rpm.... and cutting cast iron large (3" and above) at such slow speeds needs small cuts. But There is plenty of torque and power for anything I need when it is running upwards of 300rpm... Yes, I can hear (and read) the speed drop a tad when applying a hefty cut at speed - The small angle of phase slip is what motors have to do to develop the torque... or so I understand? - but nothing overheats (touch wood!) and the Chinese electrics are still good after more than 10 years abuse from me. The stop-start push-buttons did burn out though and have been replaced for about £2.50! Just "Bunce"!
ALSO: a 3-phase motor on the appropriate single phase voltage only gives around 80% of the power rating... and torque is much lower as well. (I think it is sq.root 3 over 2? - But my "electric theory" is 50 years old and memory plays tricks... I'm sure someone will correct me!).
Enjoy! - and remember, Ratings are always "Laboratory conditions on a "perfect" example of the product... Caveat Emptor!
K

 

[Richard Hed]

I will be looking for a VFD, I thimk, soon, so can anyone direct me to low priced but quality VFDs?

 

[OrangeAlpine]

I have bought two low priced Ebay VFD's and they have done their job very well. They are about 100% oversize.
Bill

 

[Richard Hed]

I have bought two low priced Ebay VFD's and they have done their job very well. They are about 100% oversize.
Bill

Can you tell me a brand name and approximate cost? When you say 100% oversize, does that mean the rating for HP is double what you motor is rated for? Does that have to do with the "Chinese" propensity to lie about ratings or the quality maybe?

 

[Richard Hed]

That is exactly what I found to be the problem, I ended up ordering a GS2 drive from automation direct and it runs perfectly. Automation directs drives are very reasonably priced and the quality is many times better than the run of the mill Chinese junk from ebay or amazon and you get 24/7 American support and instruction manuals in actual English.

When you say "reasonably priced", what range of prices, please? and do you have a link to this place?