ML7 Motor – what would you do?

[Matt C BeechParticipant @mattcbeech]

Hi,

I'm at the point of restoring the motor for my ML7, but I need to consider the ways forwards since they are both pretty old and in bad shape

1) 1/3 hp Vickers motor, but not in great shape. The cradle is very rusty and cannot be dismantled.

2) 1/4 hp Hoover motor, also not in great shape and needing work on the motor run capacitor.

3) Buy a new motor. Based on the assumption that modern motors are more efficient, better performance and more powerful for their size (I was thinking of a 4-pole ~q1500rpm 1/2hp)

Anyone have any recommendations for a new motor?

What would you do?

Matt

[Matt C BeechParticipant @mattcbeech]

[Oompa LumpaParticipant @oompalumpa34302]

Posted by Matt C Beech on 15/08/2014 22:31:36:

Hi,

I'm at the point of restoring the motor for my ML7, but I need to consider the ways forwards since they are both pretty old and in bad shape

What would you do?

Matt

I would buy a cheap Inverter from Drives Direct and look around for a 3/4 horse three phase motor and not look back.

graham.

(PS – If you really are that stuck for a motor (single phase) pm me and i'll send you one. Not new but better shape than the two you have)

[Enough!Participant @enough]

I'd agree with Graham. I got my ML7 in much the same shape as yours with a motor that wasn't much better (and had been taken apart as well).

I ended up buying a new 3-ph motor and a VFD and have never looked back.

[Russell EberhardtParticipant @russelleberhardt48058]

You can have the 1/2 hp motor that came off my lathe when I converted to 3-phase/VFD but you'll have to collect it – from the South of France. Seriously though as has been suggested above, get a VFD and a new motor from Drives Direct and you won't regret it.

Russell.

[Andrew Moyes 1Participant @andrewmoyes1]

I powered an ML7 with a 1/3hp MetVic motor for years without any problems. I agree a three phase motor and speed controller would be far better and especially advantageous on an ML7 as I’d fit a 2 pole 2800rpm motor to double the speed range. The standard top speed is too slow for most drilling. You’d need at least a 1/2hp motor, perhaps even 3/4hp to give enough torque at the higher speed and to prevent overheating under load when running at reduced speed. Don’t believe anyone who says the white metal bearings won’t take the higher speed. Mine were fine and Myford themselves offered a 2800/1450rpm dual speed motor for the Trileva version of the ML7 before electronic speed controllers became available.

[Peter BondParticipant @peterbond14804]

Tagging onto this one as I seem to be following in Matt's footsteps…

The ML7 I'm gradually putting back together has a 3 phase, dual voltage English Electric 1/3HP motor with it. It seems to have 4 terminals, 3 of them wired to lines. No obvious way of changing wiring between star and delta. I've ordered the Tee books on motors – my experience of 3ph motors is limited (mech eng only got taught rudimentary 3ph power theory) – but in the meantime I see the options as follows:

1. Find a way of wiring it for 1ph use and see how it goes. May not be possible and the amount of swarf I can see through the vents makes me a bit twitchy (and that's with no current flowing).

2. Replace it with a single-phase motor; either with resilient mounts or a much cheaper one from e.g. Machine Mart.

3. Buy a 3ph inverter and run it off that.

4. Buy a 3ph motor/inverter package and fit that.

3 & 4 I'm not certain make good financial sense – at this stage, the lathe is a bit of an unknown quantity. I've got about 3 thou of wear on the front shear for the 1st 1/3 of the bed, I don't know how good the spindle runout is yet and it still needs to be bolted onto a bench.

I'd already decided I didn't like the MEM contacter and sourced a more up-to-date NVR with emergency stop… The Dewhurst switch looks fine at least. What's puzzled me is that the wiring in those was 1ph, but the motor has the red/blue/yellow I'd expect of 3ph. Decommissioning was done with cutters it seems.

Any advice?

[Harry WilkesParticipant @harrywilkes58467]

Peter ref your motor one of those four terminals as 3 wires on it that's the star point you'll need a meter to check out the wires a cheap meter will do fine, the terminal that had the 3 wires on becomes redundant the other 3 terminal will have 2 winding wires and a incoming phase on each of them. Have just had to do the same thing on a motor I've just fitted ! If you need advice on how to pair the winding let us know.

H

[Les Jones 1Participant @lesjones1]

Hi Peter,
A picture of the terminal box on the motor would be a great help as I do not understand your description. I do not understand why you say it "seems" to have 4 terminals. Also I do not understand "3 of them wired to lines" Was lines meant to be links ? I think your first step should be to dismantle the motor to remove the swarf. Mark the endcaps and casing so the end caps go back in the same position. A 3 phase motor will have 6 wires coming from the winding. If it is single voltage then these may be linked inside insulation in the windings so only 3 come out to the terminal box. If it is dual voltage then all 6 need to come out to the terminal box. The Dewhurst switch can be used for both single and 3 phase reversing. If you use a VFD to generate 3 phase then DO NOT connect the Dewhurst switch between the VFD and motor. It could still be used to reverse the motor via the VFD control signals.

Les.

[Peter BondParticipant @peterbond14804]

As it stands, it looks like L1, L2 & L3 are connected (and an earth – I'm almost surprised). No cover plate, so I'll have to cut a new one (not a big deal, really).

I was working on the assumption that if I do go VFD, I'd use that to control reverse and the Dewhurst becomes redundant.

[Les Jones 1Participant @lesjones1]

Hi Peter,
I suspect that the top right hand terminal is the star point. This is where one end of each of the windings is connected together. If this is the case you will need to remove these 3 wires from this terminal and connect them to the 3 existing terminals with wires on. You will need to identify these wires so they can be connected to the correct terminals as Harry has pointed out. I cannot see how the terminal strip is fixed but it will need to be removed as the wires to the star point terminal must be on the back. IF your motor is the same model as Harry's then he will be able to tell you how to remove it. From your pictue it looks like the terminal strip needs a good clean before applying power.

Les.

[Harry WilkesParticipant @harrywilkes58467]

Hi Peter as Les suggested remove terminal board and give it a good clean and again as Les suggested I think you will find the other 3 winding wires on the top right terminal. I think it worth persevering with the motor so give it a good clean and get your self an inverter assuming you do not have a three phase supply, it's not hard to reconfig the winding for delta but as I said you will need a meter .

h

[Peter BondParticipant @peterbond14804]

Thanks both – I shall dismember the thing and clean it. Meters I have aplenty, so buzzing out connections is not a problem. I've found a VFD at a good price on EBay (a Bosch, so it even has a comprehensible data sheet); 2HP may have been overkill for this motor, but even this is only a short-term solution I can rig my belt grinder to use it instead.

Sounds like I might have this sorted before the books arrive…

[Brian WoodParticipant @brianwood45127]

Just a thought for the inverter drive brigade.

Put the workshop supply onto a separate earth leakage protected way to 'isolate' it from the main ELCB serving the house. All inverters need a small leakage to earth to work properly which is of the order of 10 mA and of course 1/3 the standard setting for a 30 mA. trip.

Any small leakages within the house, and especially so if a PV system is fitted [another inverter] are of course additive and without that separation annoying trips affecting the whole supply could become a real nuisance when you power up in the workshop.

We had just this sort of problem before taking that course and since then domestic peace has been restored. It became a real issue with the old tower block computer systems that didn't have battery back up and data loss from unexpected 'power failure' was close to being cited as a divorce matter.

Regards

Brian

Edited By Brian Wood on 16/01/2015 11:00:48

[JonParticipant @jon]

Best thing I ever did was mount a Brooke Compton 1hp 1ph motor on and never looked back. It transformed it in to something usable.

[Mick HenshallParticipant @mickhenshall99321]

My eyes cross whenever electrics are mentioned I am a novice in electrics and don't muck around too much with it. Over my 70 odd years on the planet I have collected motors from old twin tubs and the like and they power a Bandsaw/Disc Sander/small compressor/Lathe, an old doe mixing motor powers an Adcock & Shipley horizontal mill and a Shaper I am building is powered by a floor polisher/buffer motor giving a base rpm of 380. I give them a quick strip down & check bearings etc ok ,a check of condition of wiring and a test using my PAT tester every year. I don't understand the different types if it works I'll use it. I well understand trying to retain original equipment though but in I'm not clever enough and am in awe of those who are

Respectfully Mick H

[Phil WhitleyParticipant @philwhitley94135]

Hi Matt, The motors you have, rewired and cleaned, will be better than anything you will buy from machine mart. The assumtion that everything made today is better, more efficient, or more relaible that stuff made in the 1940/50's is generally erroneous, especially when you are buying stuff which came from China and carries a fake CE stamp. The italian made stuff is better, but not much. The three phase inverter route is a good way to go, but expensive unless you can get a s/h motor. Respect your whitemetal bearings, but also the maximum revs that your chuck/faceplate is rated for!! I would rebuild what you have, get the machine going, and look out for a 1hp single, and a 3ph motor/inverter in the future. If you are not happy with replacing the wiring, which looks to be TRS (tough rubber sheathed) which has been attacked by oil, and has gone sticky, I can help you with that, as can many others on here! just replace one wire at a time, after you have made a diagram of how the motor is connected. I have many motors on old equipment from that era, and also quite a lot of much newer equipment, that has had the original motor replaced by motors from this era because the newer motors have quit!

Phil!

[Peter BondParticipant @peterbond14804]

Well, I've had mine partially dismantled now and found:

Most of the swarf is plastic and brushes out. A blast with compressed air might shift the remainder.

The terminal plate is a case of WYSIYG – there are no other wires, it's supply to coils as seen. Still need to buzz out to work out if it is star or delta. The 4th terminal is just a post.

Oh, and the books have arrived.

[Les Jones 1Participant @lesjones1]

Hi Peter,
I do not believe it is possible to identify is it is star or delta connected just from resistance readings. If you call the three connections A, B, & C if you measure the resistance between A and B then short A to C the ratio of the readings will be 0.75 no matter if it is star or delta connected. You will have to find the ends of the three windings and see how they are connected.

Les.

[Harry WilkesParticipant @harrywilkes58467]

Hi Peter glad your progressing with the motor, just out of interest if the fourth terminal is just a 'post' have you found where the other 3 ends of the winding are ?

H

[Peter BondParticipant @peterbond14804]

If it's star connected, I should be measuring twice the coil resistance between terminals. If it is delta, it should be 2/3 the coil resistance. So, is twice an unknown variable or merely 66% of it?

All well and good, but it does rather depend on whether a trivial fag packet calculation based on the current reqs of the motor is valid for 3 phases and AC (DC is far simpler to work with!). More reading required.

The 3 wires lead into the motor; I need to unbolt them to take the end cap off completely. Best guess is they go direct to the coils.

[Phil WhitleyParticipant @philwhitley94135]

Hi Peter, Your motor is almost definitely star connected, the box on the label under the frequency should have a symbol, or S or D in it, but as far as I can see it is not marked. the star point will be on the winding itself where the other three ends of the coils will be soldered together and insulated. If you want to run this motor in delta, you will have to find this connection, unsolder the ends, solder a tail wire onto each one and bring them into the terminal box.Test with a multimeter to find the three coils. designate the three connections you already have as A1, B1 and C1, designate the other ends of the respective coils A2, B2 and C2. Connect A1 to B2, B1 to C2 and C1 to A2. put one phase of the supply to each junction. If the motor runs smoothly and quietly, but the wrong way, reverse any two of the incoming supply phases. If it runs slowly and growls, swap over the A1 and A2 connections. if it is still the same, put the A connections back where they were and swap the B connections.if no better,swap the B connections back, and continue with the C connections , and you will be sorted!

Phil

[Peter BondParticipant @peterbond14804]

Hi Phil –

I suspect you're right on the connections, particularly given the age of it. Reading the books, I'm intrigued as to how it is dual voltage without any obvious wiring links. I note that some of the VFD manuals advocate delta connection only, whereas others don't mention it at all.

The rewiring sounds worse in description than it is likely to be in practice!

[Phil WhitleyParticipant @philwhitley94135]

Hi Peter,

The motor has been rewound at sometime in its life, the varnish on the rating plate is a dead giveaway. the motor would have been star connected for high voltage, and delta connected for low voltage. Obviously this cannot be done with only three connections available, so it looks like it has been rewound in star only configuration. strip it down and see if you can find the other connections.

Phil.

[Peter BondParticipant @peterbond14804]

Interesting – why is it a dead giveaway? The thing has been resprayed at some point too – assuming it wasn't standard practice to paint the motors after assembly.

There's a nice load of resin over the insulation, so it's going to be entertaining trying to find the termination…

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