Motors for Variable Frequency Drive

[chrismacParticipant @chrismac]

Basically, what type works best?   The speed controllers I have seen only go up to the natural mains frequency, do some exist which will go faster?

I know that I cannot vary my existing mill motor as it has a centrifugal switch to change over from start to running windings.

For cutting brass clock gears, particularly small ones, I would like to achieve spindle speeds up to 4,000 rpm.

All help appreciated,
Chris

[Robert Atkinson 2Participant @robertatkinson2]

Hi,

Your question is not clear. The title says Motors for VFDs but the test asks about “speed controllers”.

VFDs are almost exclusively used with 3 phase motors (often from a single phase supply). They can go above the mains frequency often up to 300 or 400 Hertz.

Speed controllers are normally phase angle devices and actually cotrol power not frequency. They work best with universal (brushed) motors but will work with some small induction motors. Not suited to switch start or mill motors.

What are you trying to acheive?

Robert.

[chrismacParticipant @chrismac]

Sorry.  I was regarding VFD as a type of speed controller as variable rpm is what I wish to achieve.   I did not know of speed controller as a specific device.

[Peter Cook 6Participant @petercook6]

To achieve what you want you probably want a Brushless DC motor (BLDC) together with the appropriate drivers and control system.

I have a 200W BLDC motor on my Taig lathe that delivers around 4000rpm at full speed. It delivers good power down to 400rpm.

The motors and controllers supplied for industrial class sewing machines seem to be a popular (500w) choice for lathe applications, fitting to a mill may need some  work. There are several threads on here about using them.

[Robert Atkinson 2Participant @robertatkinson2]

OK, we need to know the make and model of your mill, the current highest spindle speed and the rated speed and power of the motor currently fitted.
You cannot (easilly, someone will aways argue) run a capacitor start (centrifugal switch operated) motor at significantly higher than rated speed. You can possibly go 20% higher as most motors, or at least their parts, are designed for 50 or 60 Hz.
We can give better guidance knowing the above but basically your choices are:

1/ Fit a 3 phase ac motor and VFD this is probably the best option but depends on the mill and in particular if the spindle (and any gears) will run at 4000 RPM.

2/ Fit a separate high speed spindle carried in the existing spindle. No modification to mill and as fast as you like. Reduces clearance over table but may not be an issue for your work.

3/ Fit a different tyype of motor e.g. a universal or BLDC (as mentioned by Peter) but these will need more work and may not be as good for other work. spindle speed limitaions still apply.

Robert.

[DiogenesParticipant @diogenes]

Chris, is this for your Sharp?

It looks like it would be quite easy to swap the motor for a 3~ one and add a vfd –

Are the spindle bearings tapered rollers?

..it’s certainly possible to run T/Rs at the speed you seek, whether it’s possible to run the ones that are currently fitted depends what they are and perhaps how they are lubricated & sealed..

I’m sure someone knows..

 

[Roderick JenkinsParticipant @roderickjenkins93242]

My Sharp MKII is slightly earlier but everything looks the same. The bearings are Timken tapered rollers.  I’ve replaced my motor with a VFD system and the speed currently tops out at 2500 but could be higher.  An alternative way to get a higher speed is to change the pulley ratios.

Rod

[bernard towersParticipant @bernardtowers37738]

The speed of your cutter is only half the story, a controllable table feed will compensate for your lack of spindle speed and give a reliable constant feed which gives a good finish to your teeth (less work later!).

[Robert Atkinson 2Participant @robertatkinson2]

Hmm I’m sure I made a post but it has disappeared.
According to Lathes.co.uk the Sharp has a 1/3 hp single phase 1480 RPM motor.
So a 63 framesize  250W (0.25kW) 2 pole 3 phase 3000 RPM motor with a VFD would work well as a speed upgrade. The spindle bearings will take the speed.  To get 4000 RPM you will have to bypass or invert the intermediate pulley. If you want to maintain torque at lower speeds without pulley changin you could go up to a 370W (0.5 hp) motor
The 3 phase motor will give much quiter and smoother running as well.
I’d go for a totally enclosed fan cooled (TEFC) motor.

Robert.

[chrismacParticipant @chrismac]

Thanks for your most helpful input.

The motor on this mill is bigger than the 1/3 hp mentioned in lathes.co.uk but I have not yet measured its power consumption under load, just running and turning the spindle it is 348W.  I think that I would bypass the centre pulleys and go for suitable sizes at the motor and spindle positions.   I do have a 1HP dual voltage 3 phase motor (TEFC), would that be too much for the other mechanics?

Changing subject a little, are those Chinese BangGood inverters actually good?

Regards,
Chris

[Robert Atkinson 2Participant @robertatkinson2]

Hi,
If the 1HP motor fits OK you can protect the mechanics by limiting the current and thus torque in the inverter settings. You could probably get away with running it on a 500W drive too.

Personally (and professionally) Iwould not entertain one of the “no-name” VFDs from the far east even if purchased from the UK. Their quality is poor which affects safety and are unlikey to meet certification requirements. The fact that some sellers recommend using a larger drive than the motor requires is telling. I’m sure there are plenty of people who are happy with them and will say so here though.

 

[chrismacParticipant @chrismac]

Oddly enough the 1HP motor has nearly identical dimensions to the single phase one currently installed.   I too wondered about the “no name” inverters, just too cheap.  Do you have any preferences regarding good ones?

Again, many thanks for your help, Chris

[Robert Atkinson 2]

On Robert Atkinson 2 Said:

Hmm I’m sure I made a post but it has disappeared.
According to Lathes.co.uk the Sharp has a 1/3 hp single phase 1480 RPM motor.
So a 63 framesize  250W (0.25kW) 2 pole 3 phase 3000 RPM motor with a VFD would work well as a speed upgrade. The spindle bearings will take the speed.  To get 4000 RPM you will have to bypass or invert the intermediate pulley. If you want to maintain torque at lower speeds without pulley changin you could go up to a 370W (0.5 hp) motor
The 3 phase motor will give much quiter and smoother running as well.
I’d go for a totally enclosed fan cooled (TEFC) motor.

Robert.

How about a 4 pole 1425 motor with VFD running up to 120Hz.
Mechanics of the motor are likely the same, just the winding configuration different.
You will probably get better low speed torque, whilst still getting twice overall speed.

A friend of mine runs a belt grinder that way, seemingly successfully.

Bill

[Robert Atkinson 2Participant @robertatkinson2]

Any known make. Some examples:

Schneider Electric
ATV12H037M2 370W
ATV12P075M2 750W

ABB
ACS355-01E-02A4-2 370W, ACS355-01E-04A7-2 750W

Mitsubishi
FR-D720S-025SC-EC 400W, FR-D720S-042SC-EC 750W

Delta Electronics
VFD1A5ME43AFSAA 400W, VFD4A8ME21AFSAA 750W

Availablr from various stockists like Farnell and the motor / drive specialists.

Robert.

[chrismac]

On 16 April 2024 at 12:21 chrismac Said:

Basically, what type works best?   The speed controllers I have seen only go up to the natural mains frequency, do some exist which will go faster?

I know that I cannot vary my existing mill motor as it has a centrifugal switch to change over from start to running windings.

For cutting brass clock gears, particularly small ones, I would like to achieve spindle speeds up to 4,000 rpm.

All help appreciated,
Chris

You have a single phase induction motor. It’ll run at the rated speed on mains and spindle speed is adjusted mechanically on belts etc.

Speed control is apparently possible for them but what you want is either a 3 phase or a DC motor and associated drive. 3 phase is the preferred way and will offer the widest range of options. If you want specific advice on what to buy then put up details of the machine, current motor and speeds achieved with it.

[chrismacParticipant @chrismac]

I already have a 900W 2 pole 3 phase motor with a spindle speed of 2850.   I have now fitted a Schneider ATV12 750W controller which, with the current pulley system and no belt shifting, gives me 200 – 3860 RPM at the spindle with the motor RPM reaching 3000.   I intend to remove the two belt pulley system and use just a single belt from the mptor to the spindle.  Fortunately I have a digital tachometer with an optical sensor so measuring RPM is easy, just a piece of tape sticking out from the rim of the pulley.  So now I have a conversion chart for reading on controller to spindle speed.

I like the warning notice on the controller, ‘Hazard of electric shock, explosion or arc flash’!

Again, many thanks for all your help.  Chris

[Robert Atkinson 2Participant @robertatkinson2]

Hi Chris,

You need to get the VFD into an enclosure or you will see arc flash when (not if) a bit for swarf hits the wrong bit.
The unsupported cables are poor too.

Robert

[chrismacParticipant @chrismac]

A suitable ventilated enclosure will be fitted once the DRO display is incorporated into it.  Ditto cable shortening and tidying.   If I decide to use an RJ45 remote display then the ATV12 can be hidden if not then the front panel must be exposed.

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