Meddings S68 motor

[SLM]

Hello,

I’ve a Meddings S68 floor standing, geared pillar drill, that an electrical engineer who previously owned it, converted to a single phase motor; in order to achieve smoother running, better torque and finer speed control, I’m thinking of reverting it to three phase.

I’ve posted elsewhere about the possibility of going for DC; that discussion can remain separate.

Those familiar with this drill will know that the original motor was housed within the drill head; mine was converted such that the new motor is on top of the drill head, above the original position.

My preference would be to restore the motor to that position. But there are a few issues with that:

1. The easiest way to achieve this would be to order the parts from meddings… £££, I suspect…
2. The original spec states voltage of 400v, ie not a simple matter of adding a VFD to run from my 240v single phase supply.

So, I wonder how likely it would be that I can find a suitable motor which could be cannibalised and fitted internally?

NB: I say canibalised because as far as I can tell from the manual, the body of the drill forms the body of the motor too.

Of course, the easy thing to do would be to swap the 1ph motor with the dual voltage 3ph motor from another drill that I’ll soon sell, add a VFD and start drilling holes… but where’s the fun in that??

 

[sawtooth-9]

I have a similar drill ( Strands ) which has the motor inside the casing.
Have you looked inside the machine, because it may be that the original motor is still inside ? They may simply have extended the rotor shaft and attached a pulley externally.
The original motor windings ( cage ) is held in place by 4 grub screws ( two each side ) through the side of the machine.
It's easy to open the top section of the gearbox and look inside.

 

[SLM]

I have a similar drill ( Strands ) which has the motor inside the casing.
Have you looked inside the machine, because it may be that the original motor is still inside ? They may simply have extended the rotor shaft and attached a pulley externally.
The original motor windings ( cage ) is held in place by 4 grub screws ( two each side ) through the side of the machine.
It's easy to open the top section of the gearbox and look inside.

If the old motor were left in place, would it not be turned by the new motor, and so be a generator, and thus a load on the new motor? Unless of course the old motor were mechanically decoupled from the gearbox.

 

[Spectric]

Even if it was a generator it would not be electricaly connected so no load.

 

[sawtooth-9]

If the old motor were left in place, would it not be turned by the new motor, and so be a generator, and thus a load on the new motor? Unless of course the old motor were mechanically decoupled from the gearbox.

The original motor would have been an induction motor, and would not act as a generator. And as Spectric points out, even if it did act as a generator, there would be no load.
So I think it would be worth looking to see if the old motor is still there.
The motor shaft was gear driven to the gearbox, so if the old motor was removed, they would have had to make a new drive shaft to link with the gearbox and mount a pulley.
Suspect they would just use the original motor shaft - in which case, the windings are probably still in place. So if you have the windings and rotor - you have the motor.

 

[SLM]

Sawtooth-9, I’ve found your thread and it is indeed the same machine!

Of course, the thing to do will be to open the machine up! However, having looked at the schematic, the simplest way I can see to have attached the new motor to the gear box is to have removed the old armature; the picture attached (from the manual)shows how the shaft is topped by a cap (with lubrication point) and a bearing. So if it wer me, I’d have used a motor shaft extension to bring a new chart in from above (the new motor position). But of course, there are many ways to skin a cat.

Scrutinising the parts list and manual does through up a few possible ways that the conversion may have been achieved, such as removing the shaft (original) from the armature, and mating that to the new motor (upside down). So it would be fingers crossed that the armature were left in place…

So I’m hopeful that that can be returned to factory spec pretty simply. But there remains the question of voltage, the machine being listed as 415v (3ph), so I presume some reworking of the winding will be necessary to run it with 240v (3ph)?

 

[Andsor]

I also have a Strands machine, and have fiddled about with it to make it work with single phase.
The previous owner disassembled everything and broke the main forward/backward switch. Because mine was a dual speed motor (dahlander motor) he fried some windings and so for full speed it just hums and draws current like a motherf***.
Anyhow, what I was concidering for a while was fitting a pulley on the underside of the motor. I'm guessing you have a fan mounter on the bottom under a cover. Then you could mount a motor on the side of the gearbox. Might not need to extend the axel.

 

[sawtooth-9]

Sawtooth-9, I’ve found your thread and it is indeed the same machine!

Of course, the thing to do will be to open the machine up! However, having looked at the schematic, the simplest way I can see to have attached the new motor to the gear box is to have removed the old armature; the picture attached (from the manual)shows how the shaft is topped by a cap (with lubrication point) and a bearing. So if it wer me, I’d have used a motor shaft extension to bring a new chart in from above (the new motor position). But of course, there are many ways to skin a cat.

Scrutinising the parts list and manual does through up a few possible ways that the conversion may have been achieved, such as removing the shaft (original) from the armature, and mating that to the new motor (upside down). So it would be fingers crossed that the armature were left in place…

So I’m hopeful that that can be returned to factory spec pretty simply. But there remains the question of voltage, the machine being listed as 415v (3ph), so I presume some reworking of the winding will be necessary to run it with 240v (3ph)?

If the original voltage was 415 , then it has been wired to run in delta.
To run a three phase motor at 240 volt, requires that the motor is DESIGNED to do that.
Running a delta motor in star mode - a real no no. Start, yes - run, NO.
It will VERY quickly increase revs and run to destruction. Bystanders beware !

 

[SLM]

As I’ve said elsewhere, this isn’t about making the most cost effective solution, for me; I have about £400 invested in all my machine tools (Sedgwick table saw, Startrite bandsaw, SCM spindle moulder, dominion p/t, Meddings drill, extraction system), so there’s some latitude to spend a little money on this, and not feel extravagant! And I have a use for the 240v motor that will come off this.

So, assuming the parts are there, I could:

1. use some form of phase converter to run the original 2-speed 3phase motor.

2. Mount a 240/415v 3phase motor on the top, in the same manner as the existing one, with a VFD

3. Potentially cannibaliser a 240/415v motor to mount it internally, as per the original, plus a VFD…

Hmmm… obviously option 3 is the most complicated! But I’d find it the most satisfying. It’s also arguably the most financially sensible; these older machines appeal mostly to amateur users, for whom 240v is attractive.

Would it be as simple as finding a motor that fits the dimensions, pulling out the workings and fitting them into the drill? I have several motors sitting on the shelf already.

 

[sawtooth-9]

As I’ve said elsewhere, this isn’t about making the most cost effective solution, for me; I have about £400 invested in all my machine tools (Sedgwick table saw, Startrite bandsaw, SCM spindle moulder, dominion p/t, Meddings drill, extraction system), so there’s some latitude to spend a little money on this, and not feel extravagant! And I have a use for the 240v motor that will come off this.

So, assuming the parts are there, I could:

1. use some form of phase converter to run the original 2-speed 3phase motor.

2. Mount a 240/415v 3phase motor on the top, in the same manner as the existing one, with a VFD

3. Potentially cannibaliser a 240/415v motor to mount it internally, as per the original, plus a VFD…

Hmmm… obviously option 3 is the most complicated! But I’d find it the most satisfying. It’s also arguably the most financially sensible; these older machines appeal mostly to amateur users, for whom 240v is attractive.

Would it be as simple as finding a motor that fits the dimensions, pulling out the workings and fitting them into the drill? I have several motors sitting on the shelf already.\

Good luck finding a single phase ( 240 volt ) motor to fit in the casing.
If the original 415 volt motor is still there , there is a simple choice :

Get a 415 volt supply
Or see if someone can re wind the cage to a single phase - suspect this is really NOT the way to go.

You need to open up this machine and see whether the original motor is still there - put us out of our angst.

Then let us know what you are going to do.
Are you just playing, or do you really want a sensible practical result ?

 

[SLM]

I finally got the time to open up the drill… the original windings are still there. I will take a closer look and see what i can work out.

As to @sawtooth-9 ’s question… I’m playing, certainly, but I want a working machine at the end of it!

 

[ChaiLatte]

use some form of phase converter to run the original 2-speed 3phase motor.

Sorry to quote a post that is very old, but if you want to go this route have a look at or search for 'AT4 VFD'. They take single phase 230v in and output three phase 415v.

The difficulty is the two speed aspect. It is not recommmended to switch the output of a VFD otherwise than by using its own controls. This means that a simple speed change switch between VFD and motor is risky.

You can train yourself never to operate the speed change switch while the VFD is active, but humans make mistakes...

Hence, if you can add a mechanical or electrical interlock to the speed change switch such that it cannot be operated while the VFD output is active, the problem goes away.

Simplest of all is a cover over the speed change switch with a microswitch wired into the VFD's control logic so that when the cover is opened, the VFD receives a stop signal (similar to a chuck guard or door switch on a lathe - open the door and the motor stops). Although simple, it is a bit ugly, but you can design a more elegant and integrated solution on the same principle.

 

[SLM]

Sorry to quote a post that is very old, but if you want to go this route have a look at or search for 'AT4 VFD'. They take single phase 230v in and output three phase 415v.

The difficulty is the two speed aspect. It is not recommmended to switch the output of a VFD otherwise than by using its own controls. This means that a simple speed change switch between VFD and motor is risky.

You can train yourself never to operate the speed change switch while the VFD is active, but humans make mistakes...

Hence, if you can add a mechanical or electrical interlock to the speed change switch such that it cannot be operated while the VFD output is active, the problem goes away.

Simplest of all is a cover over the speed change switch with a microswitch wired into the VFD's control logic so that when the cover is opened, the VFD receives a stop signal (similar to a chuck guard or door switch on a lathe - open the door and the motor stops). Although simple, it is a bit ugly, but you can design a more elegant and integrated solution on the same principle.

Thanks, that’s very useful!

 

[guineafowl21]

I’m not familiar with the drill. If it has a pole-switching, two speed (Dahlander) motor, then you’ve got a couple of options:

- Leave it in delta (high speed) and use the AT4 VFD mentioned above to change speed.
- Reconfigure the motor in parallel delta to take 240V and use a standard AT1 VFD, which will be much cheaper and more likely to be electrically compliant.

Either way, you would disable the speed switch as it’s not needed (or wanted) with a VFD.

 

[Spectric]

This means that a simple speed change switch between VFD and motor is risky.

You can destroy a VFD if it is running and disconnected from the load, the only way would be to have a system that ensures the VFD is off and then switch the motor windings but this can only work if the same set of VFD parameters can be used. The better option is to just configure the motor for 230 volts and use the VFD for speed control. Then if it is working with the external motor why not just use it, saves any expense or hassle.

 

[ChaiLatte]

You can destroy a VFD if it is running and disconnected from the load, the only way would be to have a system that ensures the VFD is off and then switch the motor windings but this can only work if the same set of VFD parameters can be used. The better option is to just configure the motor for 230 volts and use the VFD for speed control. Then if it is working with the external motor why not just use it, saves any expense or hassle.

You need to be very specific in what you are saying lest you give a misleading impression of the situation. What exactly do you mean by "running"? You can apply mains power to the _input_ of a VFD with nothing at all connected (not even wires) with no bad consequences.

It is only if you disconnect the load while the VFD _output_ is high that the magic-smoke-escaping probability will increase. No-one should be mislead into thinking that the "off" in your post means "the device is powered off".

The OP has stated that it is a _two_ speed motor. It is not practical to configure these to run off 230v three phase.

The VFD parameters are generally changed or set to protect the motor. So on a two speed motor, you would set the parameters to whichever speed requires the more conservative parameters (lower maximum current draw) and live with the VFD producing a very occasional overcurrent fault on the other speed.

 

[Spectric]

What I am saying is that if a VFD is driving it's output and there is no load then the output drives suffer. I have experienced this using ABB drives on some 100Kw motors and due to a wiring issue during early commisioning the VFD was not connected to the motor it was supposed to be, open circuit and the VFD failed when the motor startup sequence was initiated.

If I want a three phase supply then I would always look at using a digital phase convertor and not an invertor, much more flexable as it allows multiple three phase sockets and no modifications to the machine. On the other hand I have run several three phase motors on a 400 volt supply with the motor in 230 volt Delta configuration but for a 400 volt 87 Hz ratio to get constant torque and use a smaller motor frame.

 

[guineafowl21]

The OP has stated that it is a _two_ speed motor. It is not practical to configure these to run off 230v three phase.

Although slightly trickier than, say, digging out a star point, you can convert them reasonably easily. There are enough connections available to reconfigure the series delta into parallel. You can run at 50Hz (240V) for high speed, and 25Hz for low speed.

 

[SLM]

Then if it is working with the external motor why not just use it, saves any expense or hassle…

@Spectric … Overwhelmingly, because I’ve already pinched that motor for another purpose!

 

[robump]

Sorry to hijack the thread, but do you know if the digital phase converter can be used with a brake?

Thanks