Newman 3ph motor help

Hi all.

Newbie here so please be gentle! I recently picked up a raglan mill from a lovely chap in Yorkshire. The mill is 3 phase and he had been running it on a phase converter.

I assumed (I know!!) That I could just buy a vfd and run it off that, but it hasn't proven to be the case.

The motor itself is a Newman 3 phase. It is connected to the supply via a switch which provides 2 speeds, and an isolation type switch.

I initially connected the VFd to the 3 phase plug, however apart from some humming, no dice.

I've removed the motor, and noted it has 6 wires coming into it's connection box. Every wire has continuity with every other wire, showing either 50 ohms or 90 (ish).

I have now wired the vfd to the speed selection switch, which, when the VFd is powered, spins the motor at different speed depending on the switch position. Great! Problem is that the motor has no torque at all. When the mills belt drive is connected it cannot even overcome that friction and spin the spindle.

I have done some research on 3 phase motors, especially the very helpful guide just below this one, where the author converted his Newman motor from star to delta. Difference is that his Motor has three wires to my six.

Extensive googling has yielded nothing which gives me confidence!! Can anyone point me in the right direction to get this machine running?

I’d just buy a new(sh) motor 4 pole of at least 375watt (1/2 hp) or bigger if you can squeeze a bigger one in

make sure its dual voltage

i bought 2 last week on eBay for £40 each both new and unused

It would be more useful to see the motor's terminals please.

The 6 wires will be the ends of the 3 coils. You need to ensure that you have the motor correctly wired in delta or star as appropriate. What do the VFD's instructions say?

Edited By Chris Pearson 1 on 15/02/2023 18:42:22

Thanks for the message. I did consider that, but The motor lives inside the mill body, and the information I found on the raglan says it's extremely difficult to find an alternative motor which would fit.

Please excuse the crudeness of the drawings!!

The numbers in the grid indicate the resistance between those points in ohms

3hp or 1/2hp as the motor plate indicates? With the lower power motor, you would be best advised to get a new motor. The mounting and spindle would probably be different so it would not be a straight swap with the old one.

**LINK**

It is a 400 volt (phase to phase) motor but it is likely your VFD puts out 230 volts (phase to phase). You can get one that puts out 400 volts but they cost more than the usual cheap options.

Based on wiring diagrams I have seen for 2 speed 3 phase motors the coils require 230 volts across them. However there are six coils with 12 tails and separating them then linking some to give six tails to enable the correct wiring for a 230 volt VFD looks daunting.

Normally the VFD should be connected directly to a motor and it is recommended to not disconnect a powered up VFD from its motor by passing it through any form of switch.

Martin C

It's a two speed constant torque motor, almost certainly of the Dahlander pole changing variety, so sorting out the windings and connections is likely to be challenging. Especially if you've not done that sot of thing before.

Objectively the simple way is to feed it proper three phase, whether from property set up rotary converter or a 440 volt output VFD run at a fixed 50 Hz, which will be a close facsimile of what it was designed to run on. It's possible the the relatively inexpensive import 380 volt output VFD boxes will be capable of running this motor on both speeds if set to 50 Hz but by their very nature such devices have performance limitations. Primarily due to the love DC bus voltage.

If you are determined to disentangle things it's advisable to have a reference diagram for how the motor wiring and switch gear is connected. Presumably you don't have a diagram for the Raglan. The two speed motors used on 2 1/2  hp Bridgeport J heads do bring out all the wires which can be re-assembled by the electrician if the factory connection is disturbed so the necessary information is on the Bridgeport wiring diagram. In rather less than crystal clear fashion! Maybe someone knows of a better source for the machine - motor connections.

About 5 years ago I answered a similar question, relating to running a two speed  Bridgeport motor off an ordinary 220 volt VFD, so I have cut and pasted the relevant text.

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The common Dahlander connection two speed motors cannot be run off an ordinary 220 V output VFD because they don't have alternative low voltage (220 V) Delta and high voltage (440 V) Y connection capability. They require 440 V input for both speeds with the coils laid out Delta style for low and Y style for high.

There are six windings in the motor. For low speeds the windings are connected in a series loop with power applied to every other connection. So 440 volts is applied across each pair and the individual windings see 220 volts each. For high speed the windings are connected in parallel pairs. One end of each pair goes to a common point the other end receives power. So each winding sees 220 volts.

You can run a Dahlander motor in high speed setting off a 220 V VFD by connecting the windings in parallel pairs and running them in a series loop with power applied to each corner. Effectively each parallel pair is equivalent to the single windings on a normal three phase motor in Delta connection. Not something for the novice to try. Its very, very easy to get things muddled up with paired windings out of phase or not correctly paired. Not something I'd try. I could do it but wouldn't if you see what I mean.

Wikipedia has an adequate, albeit small, diagram of the coil layouts :- **LINK** . Google search will show up plenty more pictures but most aren't linkable. This is quite a good one showing the switching involved :- **LINK** for speed changing.

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its not something I'd care to fiddle with.

Clive

Edited By Clive Foster on 15/02/2023 19:41:02

I agree, unless someone comes up with a clever answer. With luck a Raglan owner will have sorted this out before, but I fear the worse.

VFDs are easy peasy unless:

• The motor is star wired internally for 415V 3-phase, with no way of switching to delta apart from opening the motor up and finding and separating the connection into pairs. It's usually possible, but it looks as if the motor also features the other anti-VFD booby trap which is
• The motor provides two speeds by having two sets of windings, selected by external switches. Not an ideal method when the motor was made in times of yore and I think unlikely to be done today. The usual method now is to speed control a standard single speed motor with a VFD, which has several advantages.

Looks like this particular motor has both problems; star wound and 2 sets of windings, plus an unusual size, which is why the previous owner ran it off a phase converter. Maybe he can explain his converter, and you can copy it.

Hope I've got it all wrong and my gloom is unjustified.

Dave

Edited By SillyOldDuffer on 15/02/2023 19:40:14

I would do as the previous owner and use a converter, I would check wether static or rotary. You have a good motor designed for the job. Otherwise you will have to alter and may be ruin the motor, and possibly have to rewire the switch gear for what ? VFDs are good for some jobs, but I'm not sure this is one of them. Noel

I had a 2-speed Newman motor which had two entirely separate windings for low and high speed, so it may well be a Dahlander connected motor but eqully it may not.

Rich: Have a look on the inside of the motor terminals cover there should be a connection diagram.

Edited By Pete Rimmer on 15/02/2023 20:22:54

Thanks to all for your advice. Very helpful (if not what I wanted to hear!!). Pete Rimmer, I'll post a photo of the connection box tomorrow. I can say there is definitely no connection diagram inside. All there are are 6 posts, labelled as the diagram above.

I think I could just about manage to find a star connection inside a motor, but locating and isolating all the coils is well beyond what I think I could do. Certainly it's a foolish guy who asks for advice and ignores it!!

I'll look at motor replacement, but it's such a tight fit in the mill I think I'd be very lucky to find one which fits, and as Noel says, I have one which is designed for the job, I just need to feed it!

I'll research phase converters. Annoyingly, I can't see that I'll be buying more three phase tools (already have a lathe) so a rotary converter seems like it wouldn't get enough use to justify its considerable cost.

Looking again at your resistance figures your motor IS a Dahlander connection one. Typically you would have six wires out to the pole changer switch and the three that will form the star point and 3 that are in the middle of the straights will have approx. 2x the resistance of the other combinations.

Here is a typical 2-speed reversing pole changer arrangement. In low speed the power is sent to the three corners of the triangle, in high speed the corners are connected together and power is sent to the nodes in the middle of each straight side.

In the image above if you count the contactors 1-7 from top down:

1,2 and 7 switch in high speed (1 and 2 providing phase reversing)

3,4 and 6 switch in low speed  (3 and 4 providing phase reversing)

5 creates the star point, when high speed is selected in either direction.

Edited By Pete Rimmer on 15/02/2023 21:23:15

Edited By Pete Rimmer on 15/02/2023 21:33:27

I would expect to find 3 links in the terminal box. They could go A2-C3, B2-B3, C2-A3; or A2-B2-C2 and the supply cables would be to A2, B2, C2.

Are those resistances with all the terminals independent, or with links installed?

Hi Chris

You're exactly correct on the labelling of the wires from the motor. I don't have links, but do have a large rotary switch (which I think is the contactor which Pete is referring to). That switch I suspect will change all the connections around internally to achieve what Pete suggests.

So next question, and I'm talking myself into something unwise.

If my motor is wired delta (albeit dahlander delta). Surely what I would need to do is open it up and each wire emerging from the casing will be connected to two coils. I split those coils at that point and add wires, bringing twelve wires out and having access to all windings? Am I being over simplified? My main concern was locating the join points, but if the wires emerging from the casings lead me to them, that may be achievable

Rich,

I have done exactly that thing. It's no trivial exercise but it does work to yield a 240V delta-wound motor. How successful it will be in operation is unknown for me I do know that the motor runs on a VFD but tends to whistle a bit.

Pete

I am a little puzzled why you would want to go to the trouble of converting it to low voltage three phase when 230v single phase input to 380v three phase VFDs are now so cheap and easily available. Search for 'AT4-2200x VFD'.

Clive's point above about the output of the devices being a compromise is true but only has any real force if you are trying to drive a motor near the stated capacity of the VFD. The AT4 is a nominal 2.2kW device, so it will have no problem driving a 1/2 or 1.4 hp motor - you are derating it by a minimum factor of four.

Set the VFD parameters to suit the 1/4hp mode and try it. If you get too many overcurrent faults in the 1/2hp mode, you might have to adjust them upwards and go gently in the other mode.

Pick the equivalent 230v output VFD and work out the price difference between the two. Is the time you will spend to convert to 230v three phase worth that money?

To me, you would be better spending your time thinking about a way that you guarantee that you can only change motor speeds when the VFD output is inactive (i.e. an interlock between the VFD's control circuitry and the mechanical speed change switch).