Motor query for 3 phase VFD conversion

[Mark SlatterParticipant @markslatter13251]

Hello everyone,

I have a 3 phase Baileigh turret style milling machine that I’d like to convert to use with a VFD via the single phase in my workshop. The spindle speed is currently determined by belts and pulleys, which I would like to get rid of…or at least not need and rather control the speed via a potentiometer. I was hoping for a max rpm of around 2500 if possible. Similarly it would be useful to have a jog function that operates in forward and reverse for use when tapping, therefore low rpm’s. The VFD I had in mind was the ubiquitous AT1.

I was wondering if someone might be able to tell me if the existing motor on the mill would be suitable? I have tried to do some research on forums and YouTube etc but have come away mostly confused!

[DC31kParticipant @dc31k]

The motor data plate indicates 400v three phase, connected in Y (wye/star).

To attach a VFD directly to that motor with no modifcation would require a VFD that outputs 380v three phase from a 230v single phase input. These are available as AT4 (not AT1).

A second option is to locate the star point of the motor and reconfigure it to delta connected. This can be a more or less easy job depending on how the motor is manufactured. Then an AT1 VFD would work.

[Andrew CrowParticipant @andrewcrow91475]

<p style=”text-align: left;”>You could try Power Capacitors in Birmingham, I think the person you need to speak to is Peter Moss.</p>
They do convectors and inverters and he would probably be able to advise you about motor suitability, the number is below.

0121-708-4522

Andy

[Andrew CrowParticipant @andrewcrow91475]

<p style=”text-align: left;”>Should have said converters not convectors</p>

[Andrew Crow]

On Andrew Crow Said:

<p style=”text-align: left;”>You could try Power Capacitors in Birmingham, I think the person you need to speak to is Peter Moss.</p>
They do convectors and inverters and he would probably be able to advise you about motor suitability, the number is below.

0121-708-4522

Andy

I,ll second try Power Capacitors Peter advised and sorted my kit

H

[PeteParticipant @pete41194]

A VFD doesn’t remove the need for moving the belt to different pulley positions Mark. It will lessen those changes as long as the tooling diameter and what the tooling is built from, HSS v Carbide are similar when changing those cutting tools. From my own perspective, using a VFD on my own step pulley turret mill was one of the best decisions I made because of all the extra motor control options. Yes you can get a fair amount of torque even down into the 25 Hz range, but the length of time your using that motor at those reduced speeds becomes important since the motors own cooling fan is also running at that reduced rpm as well. Extra heat the motor wasn’t designed for will only lessen it’s life span if that motor is being operated for too long at reduced rpm.

Most but not all VFD’s today are capable of either forward or reverse motor direction. If your mill does have a back gear, then you also require a VFD that does allow switching to either motor direction since that back gear reverses the spindle rotation once it’s engaged. I’d also suggest that how well the user manual has been done might be as important as the VFD itself. Without a clearly written manual, the initial end user programming for what you want to have available such as ramp up / down times, pre set motor speeds etc, can become a real issue. And as long as it’s well explained, none of it is hard to do. I also wouldn’t under size or buy any VFD that’s just barely adequate for the job. For higher than the motors rated rpm and at the highest pulley speed ratio, my own industrial quality VFD would fault out due to the extra torque required during a motor start. Increasing the motors ramp up time of a few seconds more cured that.

[duncan webster 1Participant @duncanwebster1]

Take the lid off the junction box. If there are 6 connections with jumpers it can probably be reconnected as delta

[Clive FosterParticipant @clivefoster55965]

If you simply connect a common 220 V nominal output VFD intended for use with a 220 v delta connection to a Y (star) 440 V motor maximum power will be approximately 60% of the nameplate rating.

Basically the VFD bus runs out of volts so it switches to constant power mode at about 29 hz,  just over 800 rpm.

Which may well be enough. Thats a 2 hp motor so maximum power will be reduced to 1.2 hp. I presume the mill is a Bridgeport clone, my Bridgeport has a 1.5 hp motor and has, so far as I can see, never run at anything approaching full power in my hands.

Clive

[noel shelleyParticipant @noelshelley55608]

It looks like a new ish motor, so as Duncan says take the lid off the box and see if there’s 6 terminals – the ends of the 3 windings . If so change from star to delta. Good luck. Noel.

[john fletcher 1Participant @johnfletcher1]

Whip the terminal box cover off and if there is 6 terminals its a 5 minute job to convert the motor from star to delta. But if you have only 3 then all is not lost, don’t concern yourself with over heating etc, that will come later. Locate an excellent article published on this site several years, describing with pictures how to locate the STAR point (connection) of your motor. Generally not a difficult job. Let us know how you get on . John

[Mark SlatterParticipant @markslatter13251]

Thank you for the replies everyone, I really appreciate it! I’ll have a look at the motor this evening after work and report back.

[SillyOldDufferModerator @sillyoldduffer]

These days I incline to using a 400V VFD rather than looking for the star point, breaking it, and leading out the windings to a delta.   How accessible the star point is varies.   Most people find it without much bother, a few discover it’s buried inside.  The motor has to be opened up to find out.

3-phase motors contain 3 coils.  They can be connected in either star or delta, as shown below. delta on the right:

Star is favoured by industry, who have a real 3-phase supply available.   Delta is favoured in 240V single-phase homes because it simplifies the single to 3-phase converter.   For many years there wasn’t an affordable way of converting 240V single-phase to 400V 3-phase.  Not so today.  The electronic magic exists and it’s not too expensive.  DC31k mentions the AT4. Buying a 400V-out VFD removes the need to rewire the motor.

Don’t remove the existing belts, they are still useful.  Normally the machine is left in one mechanical setting and the speed varied by VFD.  But, if the VFD doesn’t do a good job, usually at slow speed, then it’s good to drop a gear so the VFD can run the motor faster.

Gotchas!

• Machines with more than one motor, such as a suds-pump.   VFDs don’t care for extra motors or machine lamps much because they tune into the motor, and adding on another can confuse them.  Unpredictable because much depends on the motor and design of the electronics.   As the electronics needed to cope reliably with a mixed load is expensive most VFDs don’t have it.
• For the same reason, dual speed motors.
• High-voltage electrical work is dangerous.  Get it wrong and the installer, operator, motor and electronics could all come to a smokey end.   Care required!
• The VFD has to be enclosed in another box to protect it from dirt and the operator from electrocution.  The keypad provided is only for setting up, not for day to day use.   The actual controls are wired to the VFD, and usually contained another conveniently positioned box on the the machine hosting a speed pot, emergency on/off, forward, and reverse switches.  Not difficult, but if electrics aren’t your thing, worth buying a kit – VFD, box, and pendant with instructions.  The folk who sell kits have a good reputation for explaining what’s needed and then supporting the customer.

Dave

 

 

 

[old martParticipant @oldmart]

I looked at motors on the excellent Inverter Drive Supermarket and found one with a diagram of the terminal box. As far as I know, the connections are standardised, and if yours lookslike that, then a single phase VFD using 230V would work with the motor if the motor can be changed to DELTA.

As already mentioned, the belts, while being a pain to change, will suppliment the VFD giving a huge speed range without sacrificing the torque. I fitted a 1hp 6 pole motor with a VFD to the museum’s Tom Senior light vertical and kept the 4 belt speeds which allow slow speed torque occasionally. A motor running at 25Hz has only half the power that it is rated at, and reducing the frequency further really shows why mechanical reduction is a good thing.

 

 

https://inverterdrive.com/group/Motors-AC/ac-Motor-WEG-12862355/

[Mark SlatterParticipant @markslatter13251]

Many thanks again for all your help everyone, all your comments have been most helpful!

I had a look inside the motor junction box and found the 6 terminals as mentioned…that’s a win! it seems as though it’ll be a simple enough job to bridge the opposing pins to reconfigure as delta and use a 240V VFD. Although I could use an AT4 400V VFD, It seems as though there is more information available for setting parameters and trouble shooting with the AT1 version. I have emailed Newton Tesla and Transwave for a quote on a kit out of interest, but frankly I think I’d like to give it a go myself.

[Robert Atkinson 2Participant @robertatkinson2]

Don’t forget a VFD cn increase the frequency and speed as well as reduce it. Any modern 50Hz motor should run up to 20% faster (60Hz) without question. many will be marked 50-60Hz. Checking the datasheet may allow even higher.
IF you have to buy a new motor I second Old mart’s suggestion of a 6 pole motor instead of 4. These runn slower at 50Hz reducing the need for mechanical reduction. They can typically be run on a VFD at the same speed as the 4 pole version of the same model. This is 1.5 times / 75Hz. This easily gives a 3:1 speed range without significant loss of power.

It’s your choice buy my opinion is forget the unbranded far eastern drives with poor manuals and get a decent branded VFD. It might cost a bit more initally but will be better documented and probably more reliable.

Robert.

[Clive FosterParticipant @clivefoster55965]

Looks good. Nice and easy to re-configure to delta.

Inverter Drive Supermarket are good people to deal with and always competitive on price. Asks them what the most appropriate value for money VFD is and you will get good advice.

Clive

[Mark SlatterParticipant @markslatter13251]

Robert and Clive you make a good argument for obtaining a decent quality VFD, I’ve emailed Inverter Drive Supermarket to ask for their recommendation. The Invertek Optidrives look good, with decent reviews and they seem simple to configure.

[duncan webster 1Participant @duncanwebster1]

Newton tesla are a good outfit, I’ve had 4 vfds from them. They also sell prewired control boxes

 

[Mark SlatterParticipant @markslatter13251]

Newton Tesla and Transwave have sent through some initial prices but are asking about the base motor speed, i.e whether to supply a 2 pole or 4 pole motor. I realise this has been touched on in this thread but I thought I’d ask again.

Considering my requirements of a relatively low rpm, say 150, up to 3000 (I will be using some small diameter drills and cutters on certain projects), would it be better to increase the frequency of a 4 pole motor up to a sensible level (Newton suggest 60-70Hz…but perhaps they are being conservative and higher frequency might be doable) and then use belts to achieve the higher speed range or go with a 2 pole and keep the motor running at higher rpm’s to preserve torque and again use belts to achieve a speed reduction, although how practical this might be for the very low speeds I’m not sure? My first thought tells me the 4 pole might be the way to go.

 

[Clive FosterParticipant @clivefoster55965]

Mark

I’d say use what you have. Change the motor if need be after gathering experience. Whatever VFD you buy won’t care how many poles the motor has.

Recommendations for 6 pole motors are much more slanted towards lathe users where relatively large diameters have to be handled and inevitably run at lower speeds. So keeping the torque up at lower speeds is very desirable.

Milling cutters re relatively small diameter. I doubt if any of us use anything much over 25 mm / 1 inch so low end torque isn’t really an issue. Fly-cutters can be large but we rarely work them hard.

Back in the day I had a one off, market testing, Chester Lux style square column bench mill having two speed belt drive from a 2800 rpm motor under VFD control. As I recall matters the useful speed range was from around 180 rpm to 2800 rpm. Primarily governed by the pulley sizes which gave considerable overlap between the two belt settings.

Torque at high speed will not be an issue. High speed means small cutters and small cuts so the motor won’t be working very hard.

Not sure where Newton Tesla get their 60-70 hz maximum from. From what I’ve seen modern higher end motors with specifications for VFD use tend to give around 90 hz as the maximum drive frequency for constant torque operation. Higher speeds are quite practical but the torque falls off for complicated electrical reasons. The ultimate limitation on safe RPM will be the mechanical strength of the rotating parts of the motor. Considering the spinning bits are largely of the same design whatever nominal speed the motor has I guess things are probably theoretically mechanically safe to at 5,000 or so rpm assuming a quality 2,800 rpm motor running at 90 hz. How happy the bearings will be is a whole n’other matter. Especially for an economy range motor.

To a first order approximation the most basic form of VFD operates as a voltage / frequency device. Below the motors nominal speed the motor voltage is reduced so torque and hence power falls off as it runs slower. Above its nominal speed the motor voltage remains constant so torque remains constant and power rises. Internal electrical losses, which vary with frequency, and the magic of modern vector drive VFD boxes make things much more complex in the real world. But for folk like us who rarely get anywhere near needing the rated power of a motor the crude approximation will do. Compressors are about the only things we need to think properly about.

Clive

[Mark SlatterParticipant @markslatter13251]

Hello Clive, thank you for your reply. I am tending towards your suggestion of using what I have and potentially saving some money too. If the need arises in the future I can always swap the motor out. I agree torque becomes less important at the higher rpm’s and more useful in this application at lower rpm’s…just where a 4 pole motor would be happier with a VFD.

It looks as though I have a fun project ahead!

[Clive FosterParticipant @clivefoster55965]

Mark

Jumping in with a motor change strikes me as potentially borrowing trouble. A habit thats taken me best part of half a century to get under control.

The aforementioned VFD driven Chester mill had a Bridgeport R8 taper. I now run a Varispeed Bridgeport and, so far as I can recall, don’t take cuts any heavier that the Chester mill could have managed so keeping the standard motor should work fine. The Bridgeport advantage being space and working room.

As I’ve gotten older I’ve come to the conclusion that absolute speed per se is not a great issue for folk like us. With the exception of too fast which burns up cutters (and money). Not having the pressure to get jobs out of the door profitably we can adjust around slower than book speeds without great detriment. Business needs maximum economical rate of metal removal but for us that much swarf coming off that fast is an unpleasant PIA to deal with. Certainly swarf is a major limitation in how fast I work. I also suspect most home users of milling machines don’t run the cutters deep enough taking more passes than needed so slowing the job down more than any speed shortfall.

Clive

[old martParticipant @oldmart]

If you are considering doing the installation yourself and also having remote controls as the actual controls on the VFD are only intended for setting it up and not for continual use, then getting one which also has some instructions which are easy to understand will save you much anguish. As I and others recommended, the Inverter Drive Supermarket is the best place to buy from. The one in the link will suit your motor and has the pdf of the Quick Start Guide, plus has interference filters which reduce the danger of messing up your television signal, or anybody else in the neighborhood. It even has a proper remote available and the cost would be lower than a ready made system. I put the VFD for the Tom Senior mill in a steel lockable box with ventilation top and bottom and used screened cables for everything except the mainslead. Maybe overkill, but this is in a museum workshop and not a private house. It passes PAT testing regularly as it connects toi a normal wall socket.

 

 

 

 

https://inverterdrive.com/group/AC-Inverter-Drives-230V/Invertek-Optidrive-E3-1-5W-1ph-3ph-IP20/

[Martin ConnellyParticipant @martinconnelly55370]

Clive, the advantage of a higher power motor is that when running at lower than standard frequency you regain some of the torque lost by not changing belts/gears.

Martin C

[b2Participant @b2]

Hello,

 

I’ve used the AT1 on my lathe. The Newton-Tesla solution is also very nice, but I couldn’t just justify the extra cost-up. My motor was a 1HP 230V (also 400V possible, as is yours). The VFD I’ve used is the AT1-2200X and I’ve added a separate box with safety switches, speed control and an Arduino based optical tachometer (which still needs further fine-tuning) to avoid swirls getting into the VFD. All works very well, but I’ve also kept the belt for torque reasons (in my case, I’ll keep the motor speed running at at least 800 rpm for cooling reasons, nominal speed = 1450 rpm). If you’ll need more information, feel free to ask.

 

br.

 

Wim

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