VFD for M300

[Captain BigglesParticipant @captainbiggles]

[Captain BigglesParticipant @captainbiggles]

Following a most enlightening and entertaining post about hand wheel dials yesterday (**LINK**) I did say I'd be back with more questions soon.

So…

My M300 is a 3-phase machine and I've only got domestic single-phase in the garage. Transwave have suggested an VFD but I'd also need to change the motor as the one on there currently isn't dual-voltage, apparently.

But surely if I'm going to the trouble of replacing the motor I may as well just fit a single-phase one and not bother with the VFD, saving £500? Or am I missing something?

Thanks,

Joel

[KWILParticipant @kwil]

Standard M300 motor 3 phase is OK, mine was/is. Standard UK 3 phase 400V line to line. I used a Yaskawa VS Mini J7 VFD.

PM me with your email address and I will send a copy of the MEW article I wrote back in 2009.

[Anonymous]

Posted by Captain Biggles on 03/09/2020 14:45:49:

…..have suggested an VFD but I'd also need to change the motor as the one on there currently isn't dual-voltage, apparently.

Do you know that, or did someone tell you? In my manual the spindle motor part number is the same on both 415V (UK) and 220V/380V (European) schematics.

I run my M300 on 3-phase so I'll avoid the debate about VFD plus 3-phase motor versus single phase motor. Although in either case the switch gear may well not work, nor may the coolant pump.

Andrew

[Alistair Robertson 1Participant @alistairrobertson1]

I have recently installeed an M300 for a friend and I can confirm that although the motor is marked 380/440 AC volts it is in fact dual voltage. The six terminals are connected in a "star" point configuration but if you remove the brass links there are in fact three linking bars allowing you to configure the motor in "delta" mode.

We did connect a vfd and it worked fine although we didn't fully configure it as we bought a Clarke 60 phase converter for powering a mill as well. You have to remember that connecting in "delta" does reduce the available output power but unless you are really taking big cuts and trying to drill a 25mm hole in a "oner" you will not notice the difference. What you will notice if you fit a single phase motor is a reduction in smoothness of cut and of finish.

[Anonymous]

Posted by Alistair Robertson 1 on 03/09/2020 15:33:43:

You have to remember that connecting in "delta" does reduce the available output power………………

Sigh, that is incorrect. Here's the plate from the 3-phase motor I bought to drive my Pultra lathe:

The two lines for 230V delta and 400V star have identical powers.

Andrew

[Captain BigglesParticipant @captainbiggles]

Posted by Andrew Johnston on 03/09/2020 15:02:06:

Posted by Captain Biggles on 03/09/2020 14:45:49:

…..have suggested an VFD but I'd also need to change the motor as the one on there currently isn't dual-voltage, apparently.

Do you know that, or did someone tell you? In my manual the spindle motor part number is the same on both 415V (UK) and 220V/380V (European) schematics.

Thanks Andrew,

I am in contact with Transwave who said that unless it says 415/240 it's not suitable. It only says 415 and it's wound in a star (see photos, with apologies for previous owner's paintwork)

However if I can wire it into a delta configuration then presumably it'll be ok at 240?

Thanks,

Joel

[Alistair Robertson 1Participant @alistairrobertson1]

Hi,

I am only going by my experience with the M300 I worked on.

In "star" the lathe starts in it's top speed of 2800 almost instantly but in "delta" it would not start until we adjusted the "ramp up" setting. I cannot remember the figure we set in the VFD but it did start after a few seconds.

The VFD supplier said in the paperwork that there would be a reduction in torque when running in "delta"

[SillyOldDufferModerator @sillyoldduffer]

Posted by Captain Biggles on 03/09/2020 14:45:49:

…

My M300 is a 3-phase machine and I've only got domestic single-phase in the garage. Transwave have suggested an VFD but I'd also need to change the motor as the one on there currently isn't dual-voltage, apparently.

But surely if I'm going to the trouble of replacing the motor I may as well just fit a single-phase one and not bother with the VFD, saving £500? Or am I missing something?

…

Can you put up a photo of the motor plate? The experts can advise on the possibility of converting it. (I guess the star point isn't brought out to the terminal box, but it might still be accessible.)

A 3-phase motor with VFD is the bees knees compared with a single phase motor. 3-phase motors are more reliable, have better torque characteristics and run smoother than single-phase. The VFD adds speed control and other motor management improvements. Win, win apart from the cost!

Avoid single phase motors if you can, but they're not the end of the world. They perform well enough. It's just that a lathe with 3-phase and VFD is a couple of notches better than the same machine on a single-phase motor.

Quite common for people to upgrade to VFD & 3-phase motor when a trusty old single-phase motor gives up the ghost. I don't recall anyone regretting it!

Dave

[Anonymous]

Posted by Captain Biggles on 03/09/2020 16:13:37:

….Transwave who said that unless it says 415/240 it's not suitable. It only says 415….

Although the motor on the M300 is reasonably accessible my lathe is up against a wall. I've had a quick look but can't immediately see a ratings plate anywhere on my motor. Going on the experience of Alistair who has recently installed one the terminal block has six contacts which means it is dual voltage. Being a cynical old git I wouldn't put it past the manufacturer to buy dual voltage motors but mark them as 415V only in order to charge more for a dual voltage motor option.

A motor designed to run at 415V in star will expect 240V in delta, ie, divide the voltage by the square root of three.

Andrew

[Andrew TinsleyParticipant @andrewtinsley63637]

Even if the motor is star only connection, you can modify the winding connections to give a Delta set up. There are motors where it isn't possible, but they are very rare. I recently converted a load of motors from star to delta even though the terminal connection block only had the 3 phases, neutral and earth The oldest motor was a dinky little 1/4 horse, BTH motor from the early fifties.

Andrew.

[Anonymous]

Posted by Alistair Robertson 1 on 03/09/2020 16:27:35:

The VFD supplier said in the paperwork that there would be a reduction in torque when running in "delta"

I don't understand why they would say that? The frequency doesn't change, so neither does the speed. Given that the plate I showed indicates that the output power stays the same then the torque must also stay constant.

Remember that the phase currents in delta are higher than in star. So if the current limit in the VFD wasn't increased that may explain why the motor didn't start properly in delta. The start currents will also be proportionally higher so may be the VFD was going into current limit? A longer ramp time may ameliorate that.

Andrew

[Dave HalfordParticipant @davehalford22513]

There's a 250 to 415 converter still showing for sale on home workshop ad 38540 only 2hp though.

[Clive FosterParticipant @clivefoster55965]

The converter referenced by Dave at Home Workshop ad 28540 is a Motorun static converter.

Decent quality unit but very old now. 30, maybe 40,+ years I think. I had one and found it worked much better when turned into a pseudo rotary converter by adding a permanently running pilot motor. 2 or 3 hp that I had just kicking around I think. Eventually sold to a man with a Colchester Student who was well pleased.

Big issue with static converters is that they can never achieve proper phase balance, unless you get lottery win lucky and hit the sweet spot, because the capacitor values needed vary with both motor size, type and load. The maker provides a best guess approximation.

Don't futz about. Get yourself a decent brand name vector drive inverter from the likes of Inverter Drive Supermarket, the folk I use, or one of the other Forum Recommended good guy suppliers and hook up your motor. Even if it doesn't have a 6 terminal junction box opening up a relatively modern motor to find the star point is pretty easy as its generally right on top of the windings. Pretty much anything made after about 1960 will be dual voltage windings by design even if thruppence ha'penny was saved by not using a 6 terminal connection box. Older designs often have it somewhat buried.

With a good vector drive inverter used between nameplate ± 1/3 rd rpm in conjunction with the mechnical speed settings you will never notice that its not on full fat 3 phase.

Clive

[Mike PooleParticipant @mikepoole82104]

I think motors that were small enough to be started direct on would be wired in star and only three terminals provided, the emergence of VFD made it very convenient if the motor had the star and delta option available. One thing I ran into at work on larger motors was that we had the same size motor wound for 415/230 or 690/ 415, the VFD was 415v output so both motors were suitable as long as you read the plate and set the motor to suit.

Mike

[Alistair Robertson 1Participant @alistairrobertson1]

I was discussing the star/delta thing today with our old plant engineer and when I said there was no difference in star or delta windings and output he said "well why do we need Star Delta Starters for larger motors?" He couldn't remember the de-rating percentage off hand but it was always listed in the motor and starter configuration paperwork.

[Anonymous]

We're talking two completely different cases. When driving the M300 we're comparing driving a motor in star at 415V with driving the motor in delta at 240V. In this case the power output, and torque, remains constant.

In a star-delta starter the applied voltage does not change. The motor is designed to run in delta. Direct off line startup currents would be very large. So the motor is started in star (with the fixed applied voltage) so phase currents and start up currents will be lower. The currents, and hence torque, in star are about a third of the values when the motor is running in delta. So when the applied voltage doesn't change the power output, and torque, are different in star and delta. They're both higher in delta.

Andrew

[old martParticipant @oldmart]

Most of the VFD's used for small motors from domestic mains also output 240V three phase. I set the connections in the motor i bought to delta to suit that. If the motor had been left in star, it might have run, but at reduced output, as star usually used 415V.

[Author]

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