3-Phase Motor Conversions: Are They All Hype?

Having read many descriptions of how good the VFD/3-phase motor drives are for upgrading your lathe, I took the plunge & bought a set for my Super 7 from one of our reputable suppliers. Whilst it runs well, it always sounded under-powered, even though the motor is rated at 550 W (¾ hp). Even “light” cuts make the lathe audibly slow down. The other night, I even stalled the motor. With the lathe on its second highest speed, potentiometer set to “5”, and drilling out a 6 mm hole to 10 mm (in steel), I was a little surprised at this. I would not expect any problem doing this with the original, single phase motor.

So, is the VFD set up incorrectly (I left the settings as supplied), am I doing something wrong, or are the virtues of the VFD overstated? Is this behaviour to be expected at 50% speed and are my expectations too high? What are other people’s experiences?

I suspect your settings are incorrect. My S7 has never stalled and does everything as expected. Yes I do drive it hard!

I have 3ph/vfd conversions on 2 lathes and a 626 mill.....None of them lack power to turn/mill/drill or cut......

As kwil points out, it may be a setting in your inverter or a faulty motor ( likely/unlikely...the jury is still out in this one...)

Have you tried contacting your supplier and explaining the symptoms to them? If they are reputable then they ought to be able/willing to help....

Thanks for the prompt replies. It appears that I erred in assuming that the supplier would set up the VFD, as this is sold as suitable for the S7. I will have a dig around in the bowels of the controller & see if I can get it to work. Somewhat annoying because it is attached to the back of the lathe stand...

Three thoughts:

1. Make sure you know how your motor is wired and connected (star or delta configuration?) It does make a difference and the motor may even burn out if it is wrong.

2. If the inverter is correctly set up you should be getting 415v across two phases. You can check this with a meter

3. If you are unsure, please get a competent electrician to assist - 415v will kill whereas 230v usually doesnt!

On the basis that this is a domestic 240 supply going to your inverter.....and it is a 240v ac in, 0-240v 3 ph out...( make and model number would help!)

Firstly, before you change any inverter settings, Check the motor is wired for Delta and is not wired for Star. This makes a big difference!

I upgraded one of my lathes to a 3-phase motor with inverter drive, and I am very satisfied. I had to re-connect the wires from Star to Delta and enter motor specifications into the inverter drive (after reading the manual a few times). So my motor and single phase in, inverter was purchased as a package, but the motor was not wired for Delta and the motor specification was not programmed into the inverter, you are supposed to do that yourself. I hope you get it sorted, good luck,

Thor

Edited By Thor on 30/07/2018 15:57:20

I feel that it is important to remember that if you turn the motor speed down to half then you will only have half the motors rated power. If you set the v belt drive to the speed you want then the motor will be making full power at the speed you want. A VFD will not mean that you will never need to adjust the belts just that you won’t need to do it so often. Although a VFD can give full torque down to low frequencies if it is a flux vector type control, as power is torque times rpm then the power will be small at low revs. As usual you don’t get something for nothing, the laws of mechanics and electrics still apply

Mike

I have revised the controller parameters (they were slightly low, but not greatly so). Slightly improved performance, but still gutless at 50%. I fear that the motor is wired as star, not delta. Unfortunately the S7 installation results in it being almost impossible to access the connector on the motor. Checking/changing this will be a PITA!

I’ll post the results when I have dug managed to get access to the motor: this might take a while...

To answer the basic question - no!

Brushless motors and VFD 3-phase motors are great.

Neil

The cover plate is not very useful, but reference to t’internet suggests that the motor is wired as star.

You need to remove the three links connected in series first.

Then, place them as per the left image on the lid, I2 connects to W1, etc....

The links will appear side by side if you wire it correctly.

This will remedy your lathe's poor performance....

If the motor runs in the correct direction, dont swap the incoming wires...

Edited By John Rudd on 30/07/2018 17:03:11

John, thanks for confirming that the connections are wrong. I’ll rewire & try again after dinner.

I expect it is safer, for the motor manufacturer, to supply the motor wired star. If the motor were wired delta and someone (a non-electrician) connected it to a 415V three phase supply, the motor would likely be toast. As it is, the motor power would apparently be reduced to about 320W. If running at 25Hz (the 50% you mention?) it could be down to only 180W, so not surprising the lathe did not function properly.

Ndiy,

While I agree with your comments, I consider it is poor form for the reseller not to advise on the products where different modes of operation may be encountered...as in this case, a motor/vfd destined for domestic use...its just fortunate that there are folk like us on hand to help...

Buy hey....its the world we live in .....no one cares.....

Edited By John Rudd on 30/07/2018 17:59:38

1. You aren't going to burn anything out if you miswire it. Once you reconnect it in delta it should be fine. Just make certain you have set the maximum phase current to whatever it says on the nameplate and check if it's 2 pole (2900rpm) or 4 pole (1450rpm etc). You should get that right in the config too if you want to fix the issue. It would still work fine if you configure the wrong number of poles but if your display is in RPM rather than Hz, it will display speed incorrectly.

2. Wrong - you should see 230V phase to phase unless it's a special VFD that boosts the voltage internally (I think we have been told otherwise).

3. Not sure I'd go with that. 120V may be a lot safer than 230V but I wouldn't argue the toss between and 230V and 415V. I've had 415V across both hands and am still here to tell the tale but it could very easily have been curtains. I CAN tell you that it actually hurt like hell and I haven't done it again since.

Murray

Edited By Muzzer on 30/07/2018 18:10:31

There are suppliers and suppliers,some take the trouble to explain things and help,others dont bother to do either.

How do I know? Guess !

After setting the motor to the lower voltage option, get the hand book that came with it, and check the current settings, for your motor. From the motor data plate. The drive will generally go from 20hz to 50hz, but is programmable to 400 hz. Don't go over 70hz on the max limit. Some say don't go over 60z,(USA and Canada power frequency). Like others have said, as the frequency drops,so does the RPM, and so does the total power available. Also there is breaking options, and slow down/ decelleration settings. I think mine is like 0.3seconds or something like that, and have the accelleration at the same rate, on the motor start up and shut down.

I am surprised that if you brought the unit as a complete set up ready to run, that they would have the motor not in the correct configuration. I am assuming that your VFD is the 220V 3phase output one, and Not the 415V output one.

I have a microswitch inline on the S1 control circuit. This micro switch I use is a normal closed one, and is opened/broken circuit when the contact is made. It stops the lathe for when I do forward thread cutting. And allows me to turn the switch to reverse to wind back for another threading pass. Really good for internal threads. I have some pictures in my Album with it.

Neil

DrDave

Decent short description here :- **LINK** about what happens when you try to drive a motor connected for 415 volts (star) from an 230 volt output VFD. Comprehensible for the ordinary guy too. Basically 1/4 power output running at 29 hz is what you get.

All the HowToBlog entries on the Inverter Drive Supermarket are worth a look :- **LINK** . Short, not to techie and give a good feel for WTHIGO.

In my experience a good firm to deal with. Decent prices and helpful when you aren't certain what is best for your application.  Steered me to an Eaton DE1 to drive the hydraulic pump on my car lift saving me about 1/3 over a more normal VFD.  No display,  use a calibrated knob on the potentiometer if you want to know what speed you've set. preset 5 second acceleration / deceleration  ramp and preset 50 Hz output.  Use like normal starter with via start & stop buttons.  Parameters can be varied with an extra widget.  Seems much better fit for what we normally do than the usual VFD with snazzy display and foot thick instruction book describing umpteen parameters

Clive.

Edited By Clive Foster on 30/07/2018 18:28:38