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What to drive a J & S with ?

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gerry madden09/09/2021 18:44:28
212 forum posts
104 photos

I nearly pressed the button on a Warco surface grinder recently but at the last minute a J&S540 came up for sale very close to me. It ran well and the main spindle was perfect so I paid up and took delivery.

In time this might become a restoration project but right now and for the foreseeable I'm just going to play with it and make some dust at minimum. The first thing I need to do is get myself some 3phase. I called a company today that specialises in drives and, based on the fact that the machine has two motors, recommended a 3HP/2.2kW rotary converter.

I'm most definitely not an expert on 3ph electrics and have only recently read up on drives. However I'd managed to convince myself that a RC wouldn't be necessary.

The machine has two motors, one for the spindle (plated 2HP/1.5kW) and another for the lube system for which there is no plate. The manual suggests 0.5HP though).

So chaps, what do you think ? Is the RC the right solution or is there a more popular and cheaper one, albeit perhaps with some technical compromises or limitations? Your thoughts would be appreciated.


John Haine09/09/2021 19:20:01
4279 forum posts
252 photos

No not a rotary converter!! I guess the company you called sells RCs and is desperate to ship them!! Just get an appropriately sized VFD, ring up Newton Tesla and explain what you have and I'm sure they will recommend something suitable.

Dave S09/09/2021 19:44:13
266 forum posts
56 photos

I thinking you have 4 options, and the fifth would be to get “real 3phase” installed

firstly re-motor to single phase. Whilst the hydraulic pump won’t care I believe the spindle motor is balanced and smooth running and single phase motors of a reasonable price are neither. There is conjecture that single phase also produces torque ripple that is visible in the finish.

secondly use the capacitor static converter trick to start the motors, which then run on 2 out of the 3 legs, with the back emf generating the third phase. You will need to either convert the motors to 240v or get a 240 to 415 step up transformer. Also not considered a great way to run a grinder. You lose some motor torque - probably not an issue, but the unbalanced leg can be an issue for surface finish.

Third option is a VFD. This will create “proper” 3 phase, but often relies on the motor inductance to smooth the chopped waveform. Older motors and VFDs may not play nicely, meaning you may need a new motor… I do not have much experience with more modern drives, so there may be a solution that works well. You probably don’t need the variable speed, so it’s possible that will simplify things. You will need an appropriate sized one and again possibly need to step up the voltage to give 415 out ( iirc the mains gets rectified to dc then chopped back to ac so it’s possible that a vfd will also step up but I don’t remember seeing one that does)

fourth is how I run my 540 - a rotary converter. This uses the capacitor trick on an idler motor to generate “proper” 3 phase. Boxed ones also usually incorporate a step up transformer. I have 3 industrial machines (TOS FNK25 mill, CVA lathe and the 540) and have been running them with a Boost Energy unit for many (10 or 15) years.

I would talk to Newton Tesla and see if they would recommend a unit and what the limitations may be - you need to run 2 motors and its possible that might be a bad thing to do from a vfd, but I would also consider a rotary. If you get more 3 phase machines you can just wire them in to you rotary.


not done it yet09/09/2021 19:51:11
6444 forum posts
20 photos

If the drives are completely separate (as in table drive/lubrication pump and the spindle. I would go with a couple of VFDs. They may be interlocked so have to be supplied from a single power source, in which case possibly a 5kW VFD - but more likely one a tad larger. They have to be well over-sized in order to work as ‘plug’n’play.

Rotary converters are noisy and use a fair excess of power, over the item they drive - and consume power all the time they are switched on. I would think running costs of a rotary converter would be several times that of a large VFD.

A basic VFD would suffice because the programmable features would not be available when used as plug’n’play.

Edited By not done it yet on 09/09/2021 19:52:25

Robert Atkinson 209/09/2021 20:37:20
1106 forum posts
20 photos

Any kind of capacitor fix or converter will cause torque ripple and will not be suitable for the spindle motor.

With modern prices there is no reason not to use a VFD. This can be st to 100% speed with a gentle rap up and down. Smaler, lighter, quieter, cheaper and uses less electricity than a rotary converter.

The pump could use single phase with a Steinmetz capacitor arrangement see:

or swap the motor to a single phase one. However fitting a separte small VFD wll allow you to control the speed of the motor and thus the coolant flow. less noise and waste.

Robert G8RPI.

Dave S09/09/2021 20:55:09
266 forum posts
56 photos

The 540 motors drive the spindle and the motion - the secon motor runs a hydraulic pump which also supplies the ways with lube as well as drive. Not sure slowing that down is a good idea.

I am well out of touch with VFD tech, but I have not seen any evidence of torque ripple on my machines.
The three phase is well balanced according to my measurements (taken some time ago admittedly, but back then I worked for a large generator manufacturer in Loughborough) It’s also at the correct voltage.
Do VFD drives now do step up conversion as well?


David Colwill09/09/2021 21:33:56
768 forum posts
40 photos

I run mine on a rotary phase converter with no problems.

It may help if you can answer the following question.

Are you going to be working for NASA?

If the answer is no, then a rotary phase converter will be fine.

If the answer is yes then get a brand new surface grinder , the correct supply and stop trying to be cheap!


Pete Rimmer09/09/2021 21:45:16
1096 forum posts
69 photos

I fitted a small single phase motor to drive the pump on mine. Wkred perfectly fine. I also ran the main motor from a VFD but since it was a very early model with only star winding I had to get the motor apart and split the star point so I could re-wire it for delta. This too was perfectly sucessful.

Chris Crew10/09/2021 08:15:31
153 forum posts

I have a J&S 540 with three motors, four really but only three are in use at any one time. These are for the wheel-head, the table hydraulics and the selected extractor or coolant pump. I have been running this machine for the last 25 years on a 5HP rated Transwave static converter with absolutely no problems whatsoever.

I always start the motors in a particular order, i.e. wheel-head first, then the hydraulics followed by the extractor/coolant and stop them in the reverse order. The Transwave handles all this without a 'murmer' so, although the technology is probably obsolescent or even obsolete these days, it is obviously a well-designed and reliable piece of British made kit.

Personally, I am not enamoured of fitting single-phase motors to 3-phase machines, I use several Transwave static converters in the workshop and an old shop-made rotary converter, which was built by a special-effects engineer for the defunct Ealing Studios, to power a J&S 1310 cylindrical grinder. I also run smaller 3-phase machines, i.e. a Boxford shaper and a Clarkson T & C grinder with homemade start and run circuitry cribbed from the Electric Motors book in the Workshop Practice series, a small improvement to which was published in Model Engineer in the 1990's under my own name.


Edited By Chris Crew on 10/09/2021 08:17:56

Mike Poole10/09/2021 08:44:46
3099 forum posts
72 photos

The advantage of the rotary converter is that you should be able the plug the machine in and go. The inverters will require some rewiring of the machine to try and retain the existing controls. Some people find the rotary solution to be noisy but two people on this thread have gone that way. If you go for individual VFDs then I would strongly recommend installing them in a dust and splash proof cabinet as a grinder produces plenty of electronics killing dust. VFDs are made to fit in a cabinet and have minimal protection from dust and fluids. The often seen VFD screwed to a wall and plugged straight into a 13A socket is a perfect example of how not to do it so the attractive headline price of a naked VFD will probably double or triple if you make a proper job of the installation.


Chris Crew10/09/2021 10:34:54
153 forum posts

Mike, I agree with your comments.

Edited By Chris Crew on 10/09/2021 10:37:09

Bob Rodgerson10/09/2021 13:03:43
609 forum posts
174 photos

I run a Myford MG 12 using a 4Kw rotary inverter and have not had issues with surface finish. However, I have to agree that they are noisy which can be tiresome on any long jobs. They are quite large and take up a few square feet of floor space, in order to save floor space I built a shelf for mine to get nit out of the way.

old mart10/09/2021 16:16:02
3418 forum posts
210 photos

You might consider changing the small motor for a single phase one and then buying a VFD to run the main motor from the mains. You will have to set the maximum running speed to match the wheel safe limits.

I can recommend the "inverter drive supermarket" and look for a VFD the same rating as the motor and one that also includes their own "quick start manual" which will save you many wiring up and programming headaches.

Nigel McBurney 110/09/2021 16:27:13
947 forum posts
3 photos

I had worked with J &S at work and they were fine and well respected machines,,I bought a used one at auction whena company went bust and had been in use and had an overhaul a little while before I bought it, I ran it off a rotary convertor,now this converter is still in use ,and has been used to drive a turret mill ,Meddings drill,A & S horizontal mill ,Do ALL bandsaw,S & B lathe,without problem, but I could never get a really good finish on the work. Then a friend called and advised that there was a good 540 for sale by a company he had sold the 540 very cheap,so I bought it and had similar problems with finish, also a Colchester 2000 did have finish problems on a separate static conveter,I jury rigged a temporary single phase motor to the 2000 and the finish improved.Health and down sizing saw the 2000,and the J & S sold, so I never solved the problem,just by chance I met someone last week end who has a good workshop including a 540 and he runs it with two vfds,bought from far east and programmed by him , the 540 runs well on the vfds, sp I think the VFD is the way to go. I now run a Elliott 00 and have fitted a Newton Tesla motor/vfd package and it has been a success,some of the problems may have been due to living in the sticks with supply by overhead lines. If a rotary converter is chosen,then I would recomend a Transwave unit,I have used ther makes of converter but consider the Transwave to be the best,

Robert Atkinson 210/09/2021 18:51:40
1106 forum posts
20 photos

To be clear, a PROPER rotary converter is fine in terms of torque ripple (smoothness) etc but they tend to be large, noisey and power hungry. Modern VFD are now cost effective even without the reduced power consumpton. The "static" converers based on capaitors and possibly step-up transformers do not provide proper 120 degree phase shift so cause torque ripple.This can have adverse affects on surface finish and possibly machine reliability.
There is really no reason for not using a VFD or fixed speed solidstate single to 3 phase converter these days.

Robert G8RPI.

Dave S10/09/2021 19:07:47
266 forum posts
56 photos

Robert - you seem to know about the subject- can modern drives take 240v single phase and output 415 three phase, or do they still require a 240v three phase motor?


Mark Rand10/09/2021 21:06:18
1086 forum posts
12 photos

The one I run my shed with (3ph J&S1400, Hardinge HLV, Beaver mill, BCA Mk111, and Wolf grinder) is 240 in 415 out sourced from drives direct. it's a normal VFD modified by them to have a voltage doubler instead of the normal rectifier inside.

My previous setup was a superannuated Danfoss VLT 5000 series drive that i was given for a tenner.

Both ran/run any of the machines without modification. I can't really run more than two or three machines at a time without help from her indoors, but that many aren't a problem...

Andrew Johnston11/09/2021 10:25:39
6323 forum posts
679 photos

I can't help with the original query as I run my surface and cylindrical grinders from a true 3-phase supply.

A VFD that inputs single phase 240VAC and outputs 3-phase 415VAC is conceptually simple from an electronics point of view. However, I've never seen one for sale commercially. One issue would be that the maximum power rating would be fairly low due to the limited power that can be drawn from a single phase outlet. I also suspect that there is little, or no, industrial demand for such a device, so they're not produced.


gerry madden19/09/2021 12:46:20
212 forum posts
104 photos

Right chaps, I've had some time to consider all the good points made and really appreciate your guidance. I'm probably 80% convinced that a 'non-mechanical' device is the type I should go for.

My 20% of doubt centre around the fact that :-

1) I don't want any compromise in machining quality (This was the very reason to get a J&S instead of f a Warco)

2) I don't want any loss of torque

3) want essentially plug and play, no motor modifications, splitting circuitry etc. I have enough to do without adding the the 'to do' list

Im sure if I keep researching I will eventually find what I need but its a jungle out there, at least for the electrically uninitiated. In the meantime I have a few questions that I hope someone can answer for me:-

A) Power rating - My motors name plates give mech output power (kW) and input power (from VxA). Should the drive be sized on the input or output ?

B) Cost aside, is it best to match the drive power closely to that of the motors or significantly exceed it ?

C) There are a very limited number of drives that say "1ph240V input and 3ph400V output". What is the reason for this? If I were to get a 240 > 240 converter, this WOULD be a torque compomise wouldn't it ? Or am I missing something ?

D) Some say one should switch the largest motor on first (the wheel head) followed by the smaller. In my case the name-plate rating of the two motors are 1.5kW and 0.55kW respectively. What I'm thinking here is that the wheel isn't under any load until its cutting metal so its current consumption might actually be lower than that of the pump motor that will be operating under full load immediately. So does it really matter which goes on first ?


Dave S19/09/2021 13:15:12
266 forum posts
56 photos

Drive sizing should be based on the VA rating of the motor - how much it will consume. Output power is less than this because of various inefficiencies.

3 phase motors can be wound for different voltages, and in different ways. In general the difference between a 240v 3 phase and a 415v phase is that the star point of the windings is connected on one of them (can never remember which way round) - known as star or delta winding.. The star point may be available in the motor connection box, or it may be buried in the windings. You can often get to it, but with some amount of faff.

If the star point is not available (depending on age quite likely for an industrial machine spec’d for 415) you need to put 415v into the machine. If it’s available then reconfiguration will mean it can run on 240v 3 phase.

I think tthe lack of VFD in 240 in to 415 out is that there is not much demand for them. Modern motors can be configured to 240, and not having the increase the voltage in the drive makes it cheaper.

When I examined this originally (15 ish years ago) my Mill has a Dhalander wound 415v motor, and a number of other 415v motors, so it was simplest to go Rotary converter. Since then I have added more ex industrial machines and I just plug them in. Might not be the most economical way to run them, but the only time I notice larger electric bills is if I’ve been doing a lot of welding - the machine shop doesn’t seem to use that much (although I haven’t actually quantified how much)


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