Help Wire 3 Phase 2 Speed Motor

[Allan DayParticipant @allanday33071]

I have a Weiler Matador lathe with a 2 speed 3 phase motor (Dahlander.) I want to run the motor on single phase 240V 50Hz.

I want a VFD to supply the power to the high speed windings in the motor. Pictures below of the motor connection box, connection box label & the motor information plate.

How do I wire the VFD into the motor connection box & configure the 6 terminals in the connection box?

 

Would I be better off buying a new 3 phase 2.5Kw motor instead of using the original motor? I would like to use the origional motor.

 

Is a 3Kw output VFD adequate for the task?

 

Thanks for your help,

 

Allan

[DC31kParticipant @dc31k]

An option with least faff but possibly more financial implications is to buy a VFD that takes 230v single phase input and gives 415v three phase output.

These are available (very expensive) from Drives Direct, from JFK Electrical in Ireland and from far East suppliers. The generic name in the past has been XSY AT4. See this past thread:

VFD. XSY AT4 220v 1phase to 380v 3phase advice sort

You would need to have some procedure such that the speed could not be changed while the output from the VFD is active*. That could be as simple as a flap over the speed change switch that cuts the VFD output when it is opened.

* perhaps  a more general version of this comment is that it is frowned upon for there to be any switching from whatsoever a source downstream of the VFD while its output is active.

[Clive Brown 1Participant @clivebrown1]

Drives Direct offer a 3hp 415v drive on eBay, but it’s just shy of £900. I think I’d consider a new motor. Do you want the variable speed of a VFD? If not, a single phase motor would be £300 at most.

https://www.ebay.co.uk/itm/383777994422

[noel shelleyParticipant @noelshelley55608]

Unless your set on having 3Ph and the original motor I would keep your eyes open for a 2.2Kw 220V single phase motor. They are bigger than a 3Ph unit and do turn up at sensible prices. Saw tables use them as do better pressure washers Etc. Over the years I got my hands on 3 for free. Your looking for a 2 pole 2800rpm motor.

PLAN B Whilst every body goes for 240v inverters it might be considering a converter to 415v (one name is Transwave )then all the control gear Etc should work as it was designed to. Where abouts are you ? Noel.

[SillyOldDufferModerator @sillyoldduffer]

Allan’s lathe is fitted with a specially wound 3-phase motor where 2-speed operation is achieved by switching the windings.  It isn’t a bog-standard 3-phase motor, and it’s not simply a star-delta / 200,400V problem.  The motor plate describes it as a delta/wye wye, not a delta/wye.

Reasonably good description of Mr Dahlander’s genius here.   In early days of electricity it proved fairly easy to speed control DC motors, but DC power is hard to distribute efficiently.   AC solves the distribution problem, but AC motors proved  very difficult, and speed controlling them was initially thought to be impossible. Tesla’s breakthrough was extended by others, notably Heimholz and Dahlander.   Unfortunately, speed control remained elusive because at the time there was no practical way of altering frequency.   So, AC machines requiring speed control jump backwards through hoops to get it – gears, belts, and more complex forms of mechanical speed converter.  Maybe a massive mercury arc rectifier so a DC motor can be used.   Dahlander alleviated the problem with his 2-speed AC motor; they’re only found in high-end kit because of cost. The control wiring is somewhat complicated too:

 

Although 380Vac can be provided by an inexpensive Far Eastern VFD (example), that’s the least of the problems.  Affordable VFDs have two significant limitations, both breached by a Dahlender 2-speed motor:

• As the inductance of the windings matters, VFD outputs are tuned to a single winding set.  Connecting the output to a different set of windings is going off-piste, results undefined, and it might damage the motor and/or the VFD.  RED ALERT: the Dahlander has a pair of 3-phase windings.
• Disconnecting a VFD output whilst delivering power is a no-no.  The problem is that the windings can behave like a car-ignition coil, generating many thousands of volts.   The spikes can easily destroy the electronics or wreck the motor by puncturing the insulation deep inside the windings.   RED ALERT: the Dahlander changes speed by switching live phases, see contactors K1, K2 and K3 above.   3P also breaks the rule.

Options:

• Pay for a 3-phase supply.  (Worth asking, don’t be surprised by a massive quote or outright refusal.)
• Buy a VFD that allows switching.   (Expensive!  Industrial supplier.  Price on Application,)
• Install a rotary converter. (More affordable, starting at about £1500.  Hard to find 400V.)
• Design an ordinary VFD solution that doesn’t break the rules.   (Hard!  Two VFDs maybe? Skilled work.)
• Change the motor.

I’d change the motor; Dahlender 2-speed was a good option before VFDs, now they’re an expensive embarrassment. I doubt anyone would specify one in a new design.  Might sell for good money on ebay too, anyone who has to replace one is likely to be desperate!

Several motor choices:

• Single-phase.  “Good enough”  rather than good!   Poor start torque, vibration, and forget speed control.  Big single-phase motors are more trouble than small ones.  I think a Weiler deserves better!
• DC motor.  Good speed control and torque but the electronics above a kW become interesting.   Good choice for small machine tools, less so for big ones.  And the brushes wear out!
• 3-phase with VFD.   Lots of problems go away.  Smooth, easy speed control, many off-the-shelf solutions including packages with instructions and support.  Plenty of advice on the forum and elsewhere.  Mass-produced and affordable.   VFD speed control of a single motor is simpler than a Dahlender.
• Brushless DC with controller.   These are gradually pushing 3-phase motors aside.  Similar to 3-phase with noticeably superior performance across the board, and they are more efficient.   Becoming mainstream.  Not checked the practicalities recently, but costs are dropping, instructions getting simpler, and packages are available.    Many report good results by adapting Chinese industrial sewing machine motor/controller combinations, which are very affordable.   Bit small for a Weiler – up to about 1.5kW,  I believe.

Though 3-phase with VFD looks good in theory, I’d have a good hard look at the lathe’s drive train.   Judging by the excellent lathes.co.uk, this is elaborate (remember jumping through hoops backwards!):

Buyers of both Matador and Condor were offered a choice of two drive systems, the Type W and Type VS. Intended for use by toolmakers, the Type W used a mechanically operated, infinitely variable-speed mechanism that, with a 7 : 1 drive ratio and fitted with a 2-speed, 1 – 2 h.p. motor, gave stepless spindle speed changes (on 50 Hz) from 28 to 350 r.p.m. in backgear and from 160 to 2000 r.p.m. in direct drive. The Type W is easily recognised by the large drum control wheel fitted to the front face of the strand immediately below the headstock. The Type VS, intended to be more efficient for general work and production processes, was equipped with an interesting oil-bath-lubricated, pre-selector gearbox that, when driven by the standard-fit single-speed 3 h.p. motor, gave spindle speeds from 30 to 620 r.p.m. in backgear and 170 to 3550 r.p.m in direct drive.

The Dahlander motor is part of a more complex system.    If the motor is replaced, the need for a complex mechanical drive train diminishes.  With luck electronic and mechanical speed control provide the best of both worlds – I believe the mechanical system is usually set to a compromise position and rarely moved. It isn’t how the lathe was designed to work.  Or the other way round, the VFD simply switches between two fixed speeds.  I doubt leaving the mechanical system in a fixed position would be a problem, but it’s uncharted territory for me.

I’d love to chat with a Myford TriLeva owner who has fitted a VFD.  Does he still move the levers, or does the VFD make them redundant?

Dave

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