Myford 3 phase motor upgrade

[Ray LyonsParticipant @raylyons29267]

Brian, yes you can buy cheap and get away with it. The motor on my Myford began to rumble so I looked at replacement by conversion to 3Phase. At first I bought a 1HP inverter from Drives Direct and then managed to pick up a 3/4 HP motor at an auction for £1. This combination worked well and I was so pleased that the decision was taken to fit a 1 HP motor obtained as a bargain package from Drives Direct. While preparing to set this modification up, I found an inverter on EBay for £7 so I installed this with the 1 HP motor and it has worked for many years now. The new inverter I used on my shaper which also works well.

Perhaps the best of all is the conversion of the mill/drill. This was fitted with a 1 HP single phase motor which has been replaced with a 11/2 HP 3ph given to me by a neighbour as he was about to send it to the local dump. I bought an inverter from Gavin Oseman, second hand, which has been trouble free for at least 10 years. Present project is to fit a 2 HP 3ph motor to my Warco BH600 lathe. The controller was bought from Gavin Oseman and the motor,brand new, was bought from a bottled water company which was closing at a cost of £25. The controller cost about £100. This is now rigged up on the bench for testing and hopefully will be fitted this winter.

In case you are wondering what happened to the 3/4 hp motor, well, this is being lined up to replace the 1/2hp 1ph on my pedestal drill.

I hope this gives you encouragement to look around and see what is available. After all, if a £7 inverter goes wrong, you can just write it off to experience and buy another, not as cheap perhaps buy less than the expensive packages on offer.

One thing I forgot to mention is the remote controller. This needs wiring (all low voltage) and fitting in a box near to the lathe controls. These consist of small switches and a 10ohm pot, which can be found at Maplin or CPC.

[john fletcher 1Participant @johnfletcher1]

For the control circuit you can use multi cored screened cable from ex computers leads. As the above states all the switches can be obtained from Maplin or any other electronic shop/ The pot needs to be a linear type NOT volume control there log. Some inverter controls are 5 K ohm, I notice the above says 10 Ohm I'm sure that is a mistake it will be 10 K ohm. 3 phase motors are around and it not difficult to alter the connection and the worst thing you will do is blow a fuse. We read that inverters need a special motor design for them, well that might be so in industry but for us hobby type we won't notice the difference. I have 3 inverters all 2nd hand, three 3 phase motors and they were pre owned. I think all the technical details of all the makes of inverters are on the net. Give it a go, but please ensure that all the metal work included the motor are adequately earthed.Ted

[Ray LyonsParticipant @raylyons29267]

Sorry for the finger trouble. Should have read 10K ohm.

Ray

[Brian AbbottParticipant @brianabbott67793]

Big ask i know..but would anyone have a wiring diagram for a pendant i can use on a Jaguar Cub Inverter ?

I have looked at the one Neil used, but am a little confused. Both the start and stop switch are shown as open but the description says the stop switch should be normally closed.

thanks in advance..

[Michael BriggsParticipant @michaelbriggs82422]

All,

At the risk of starting a post that may go on for a considerable amount of time I would like to share the following with you.

I feel duty bound to explain a significant point in the safety of inverter installations, as has been previously described, the control inputs are normally low voltage, 12 or 24 volts, sometimes even 5. The start stop arrangements of inverter inputs are not as safe as you may assume. Consider the start input, 24 vdc or less is required from a momentary contact for a few milliseconds. With enough electrical noise on that input the drive could start while you are tightening the chuck or something else.

In industry we have to provide a more robust method of protection either disconnecting power from the inverter, disconnecting motor from inverter which has to be carefully controlled to a standstill before disconnection or the inverter can end up in smoke or there are new generations of inverters that have safety terminals to isolate the control electronics.

It is unlikely that an inverter would start up when your fan heater kicks in but there is a risk, I just have to make you aware of it. You can adopt a safe method of working of course, disengage your lathe clutch when making adjustments or isolation of power for other machines.

I am not trying to put anyone off, most of my machines are inverter controlled and better for it.

Reading what I have typed makes me sigh a little, I am an engineer not a safety officer, my post makes me sound like the latter, oh dear ……

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Michael Briggs on 08/10/2014 18:48:34:

All,

… Reading what I have typed makes me sigh a little, I am an engineer not a safety officer, my post makes me sound like the latter, oh dear ……

.

Wise words all-the-same, Michael

Thanks for giving us all a sanity-check.

MichaelG.

[MuzzerParticipant @muzzer]

"Truth be known I have debated dropping the myford in favour of a new Warco or similar but cannot bring myself to do it.."

You should definitely get a bigger machine but unless you died recently, that is no reason for getting rid of the Myford. How about a good used Warco or indeed another used larger machine? Best of both worlds!

Merry

[JonParticipant @jon]

Quite agree Muz, money better spent putting towards a larger decent lathe and junking the Myford. That's the best thing I ever did and wondered why I persisted for so long, no brainer.

First thing you will notice over a heavily modded ML7 is what takes you 4hrs no pun or exaggeration more wasted time in stock config, with a slightly larger lathe can do same job in 10 mins.

[MuzzerParticipant @muzzer]

As a product development engineer who has spent the last 30 years bringing industrial and automotive power electronics products into production, many years of that spent getting those products tested and approved to various global safety standards, I would put the risk of this kind of incident being extremely low. Of course it depends to some extent how sensibly the system has been assembled and connected up but even so, the level of safety margin required to meet requirements for exposure to radiated and conducted energy is quite significant. Don't want to sound defensive, just give a different POV.

I can't argue against the suggestion that disconnecting the drive (unplugging it) is sensible when working with the machine open but it's rather like disconnecting the battery in your car – you might do this during major vehicle surgery but not every time you park your car. Automotive and industrial (and consumer) products have different test methods and limits but they are all required to meet similarly comprehensive and quite stringent standards. I leave my inverter running but stopped while I'm between operations, as it's not practical (or good for it) to keep cycling the power on the inverter. But it is always sensible to treat machines as dangerous animals!

Murray

[Michael BriggsParticipant @michaelbriggs82422]

Hello Murray,

I don't disagree with you on your automotive exploits, I just want to express to the readers of this thread of some of the risk involved, isolation of inverters has been mandatory for at least 25 years when applied to the machines we typically use in our workshops so please be assured that the risk is not extremely low.

Regards,

Michael

[Russell EberhardtParticipant @russelleberhardt48058]

Posted by Michael Briggs on 08/10/2014 22:32:00: isolation of inverters has been mandatory for at least 25 years when applied to the machines we typically use in our workshops so please be assured that the risk is not extremely low.

I'm afraid that doesn't necessarily follow. Are there any published statistics for such accidents? Usually the requirement for isolating machines fully when being worked on is to prevent others starting the machine while it is being worked on.

The probability of interference on the control lines starting the motor is extremely low. The screening recommended for those lines is to prevent the digital signals creating RFI.

Russell.

[martin perman 1Participant @martinperman1]

Gentlemen,

The industrial washing machines I repair and service have contactors between the inverters and pumps, the inverters are sitting in idle mode until the contactor is closed and allows the inverter to start, it wouldnt be that difficult or expensive to fit a contactor in line with the inverter and motor.

Martin P

[chris stephensParticipant @chrisstephens63393]

Someone is going to say it so it might as well be me, the inverter makers recommend direct connections between VFD and motor, contactors are not recommended between the two.

[martin perman 1Participant @martinperman1]

Only stating what my company does.

Martin P

[Brian AbbottParticipant @brianabbott67793]

Thanks all for the advice..

I understand there are cheaper alternatives for what i am trying to achieve,

but based my total lack of all but the most basics of electrical & electronic engineering i have decided to entrust this to others..

Spoke to Peter at Transwave who gave me all the advice i needed..

All i need to do is decide between a metric or imperial motor..

One thing i would ask..

Once setup, what would be the general belt setting..do you leave them all set for top speed?

Thanks again

 

Edited By Brian Abbott on 09/10/2014 13:14:41

[JonParticipant @jon]

Posted by chris stephens on 09/10/2014 12:15:01:

Someone is going to say it so it might as well be me, the inverter makers recommend direct connections between VFD and motor, contactors are not recommended between the two.

News to me, whys that?

Just that have been running an inverter for 4 years in an industrial environment through original machine contactors in the way the machine was made.

[Harry WilkesParticipant @harrywilkes58467]

Posted by Jon on 09/10/2014 13:26:14:

Posted by chris stephens on 09/10/2014 12:15:01:

Someone is going to say it so it might as well be me, the inverter makers recommend direct connections between VFD and motor, contactors are not recommended between the two.

News to me, whys that?

Just that have been running an inverter for 4 years in an industrial environment through original machine contactors in the way the machine was made.

Chris is quite right in what he states this is taken from the Jag instruction manual see screen shot

[JonParticipant @jon]

Thats just a cheap inverter, granted.

There are plenty of 'Plug and Play' inverters around designed to supply a workshop or individual machine exactly the way it would be sent by your electric supplier. I use one.

[Neil WyattModerator @neilwyatt]

The reason is that the inverter is a much less 'stiff' supply than the mains. Drop the load of one puny 25kW motor in or out and the national grid doesn't notice.

Suddenly cut the load from an inverter and the output could potentially be damaged. Even more likely is damage if the inverter is running and the motor is suddenly switched in.

That's why they advise that switching is before not after it.

neil

[Ray LyonsParticipant @raylyons29267]

Perhaps working on small machines, I did not take into account the possibility of an accident by the motor starting unannounced although when using the mill I always switch off because the main switch is alongside the controller. On the Myford, not had a problem yet but you never know, when I go into the shed tonight, will ensure that the supply is switched off.

For many years I had a big old Southbend lathe. It was about 9" centre height and 5ft between centres, driven by a 11/2 hp motor using flat belts. I look back and now believe that this was the best lathe I have owned. That was a great metal cutter but a house move meant that because of space restrictions it had to go and was eventually replaced by a Warco BG600. What a contrast, there were no safety features on the Southbend where as the Warco has micro switches which cut the power to prevent accidents.

Going back to the inverters, I plan to fit one to the Warco and wish to retain the safety features and plan to wire in the inverter to the motor terminals on the existing loom. I will then be able to power up using the existing starting lever, making adjustments for speed etc., on the inverter remote. This will mean that when ever the lever is put into the stop position or any of the guards opened, power will be cut to the inverter. Hopefully, this will not be frequent since I would normally use the inverter control to stop for measuring but can anyone tell me if cutting the power to the inverter will do any harm.

[Michael BriggsParticipant @michaelbriggs82422]

Neil is spot on with his comment, if you break the load form a running inverter or connect a motor to a running inverter output you can damage it.

If you cut the power to a running inverter it should not damage it though you will lose the useful feature of the inverter ramping the motor down to a standstill, there is a recommended limit to the number of power ups that should be applied per hour normally stated in the manual.

I am a bit short of time just now, I will post a reply a little later on what might be the best way to modify your Warco.

Regards,

Michael

[JonParticipant @jon]

Ray I wouldn't keep cutting power to the inverter, I scrapped a £650 one in 1hr 25mins.

If its wired in right any stop, start and control functions will work so if levers off the inverter cuts power so would any useless guards and other controls on trips. A 1ph to 3ph 220v inverter to run the BH600 would run off domestic mains so use that to switch off and isolate when working inside or on the electrics but not for repetitive measuring where stop start levers good.

[chris stephensParticipant @chrisstephens63393]

Hi Ray, if you haven't watched it yet a YT video from Shadon HKW called "2 speed motor VFD application" might help you to show how to safely keep your safety interlocks, just ignore to part where discusses two speed. and drum switches.

chriStephens

[Michael BriggsParticipant @michaelbriggs82422]

I have to give a direct reply to Russells post, I have not persued any statistical reports for accidents by the unsafe installation of inverters because I am frankly aware that if any of the operators at my place of work were injured by any inadequecy of the installation, I would probably end up in court with the possibility of a sentence.

[Neil WyattModerator @neilwyatt]

If you check out my article here:

3-phase-conversion-and-other-alternative-methods-of-powering-a-mini-lathe

You can see my approach to having soft stop and start as well as 'emergency stop' all done through the inverter.

If I decide to fit auto stops, then they will only need to be normally closed (low voltage) microswitches in line with the e-stop button.

Neil

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