Speed control of single phase induction motor

[dennishoy]

Folks,

I have a lathe and a milling machine, each with a single phase induction motor. To change motor speed, I have to move 2 x Vee belts on the lathe and mess around with levers on a gearbox for the milling machine. The speeds are fixed and I would like to make them variable up to the full speed of the machine.

I would like a speed controller for the motors of each machine. I was considering trying one of the single phase to three phase inverters, but connecting the single phase motor across only one of the three phase outputs and setting the internal controller parameters to ignore the requirement for a 'balanced load'. I would set the belts for maximum lathe chuck speed and then set the maximum inverter frequency to 50Hz. The lathe should run no faster then normal maximum speed on this setting, but I should be able to reduce the speed to near zero using either a potentiometer or the digital control panel. I have no requirement to run the motor faster than normal (50Hz).

I do not want to change the motors for 3-phase types.
I do not mean one of those cheap Chinese inverters with no starting torque that seem to be sold only on ebay. I was thinking of the high quality Vacon NXL types (made in Finland) which are currently available quite cheaply as NOS.

Any thoughts would be much appreciated.
Thanks.

[Refugee]

I would swap the motor out for a DC type and use a simple analogue servo.
AC motors have to be manufactured to operate at variable speed from new otherwise they are likely to produce poor torque or overheat. The AC machines that many of us pick up for home use were built from new for production use and the fiddly speed changing was only ever carried out between production batches.
It is not going to be easy.

[ppppenguin]

I was at Brian Cuff's house (BrianC on VRAT) recently. He has a Bridgeport mill in his garage which he uses with a 3 phase motor and an inverter. I think it's the original 3 -phase motor though I can't be 100% sure. He says it's superb with smooth and easy control. He's thinking of changing his Myford lathe to a similar system. Didn't see either in operation but I'd be inclined to believe him. Single phase induction motors will always be less smooth, powerful (esp at startup) and controllable than their 3 phase cousins.

[Eddystonepete]

Hi All, I,m using an ABB ACS150 single to 3 phase controller to a 3 phase Marelli 0.5 hp motor on a ML7. Good points, ability to slow start and fast stop, controls easily remoted to push buttons in my favourite die cast box!. Been in use since 2009. at todays prices about £100 for controller, £50 for motor. Trying to use a single phase motor with a 3 phase controller would be fraught with problems, think about the starting capacitor and centrifugal switch. Peter

[Yorkie]

Looks a good option Peter.

Some links to the ABB ACS150 controller and Marelli 0.5HP motor:

http://www.inverterdrive.com/group/AC-In...fault.aspx

http://www.ebay.co.uk/bhp/3ph-inverter

http://www.inverterdrive.com/group/Motor...fault.aspx

My Nova woodturning lathe is eight-speed belt change and uses a 1.5HP motor. It's no big deal for me to change speed by moving the belt from one pulley to another - it only a minute's job and if ever the 1.5HP motor fails, I'll change it to 3-phase and an invertor, though that would cost upwards of £350.

Nova (A company that originated in NZ and still has its head office there), also do a variable speed lathe with the motor built into the headstock and the inverter underneath it. I obtained lottery funding to buy one for our woodturning club along with other equipment about 5 years ago, but wouldn't entertain one myself. The invertor and motor are enclosed and get quite hot, not helped by dust that gets into headstock via ventilation slots and settles on the heat sink. With the motor being integral to the headstock, if it fails, the lathe is virtually a write off. The equipment is now made in Nova's factory in China - not in NZ.

I've attached a pic of Nova chuck jaws that I mentioned some while ago which shows that despite Nova's assurance of tight quality control at its own factory in China, from my experience, this is not borne out in practice. The jaws are made is sets of four and marked 1,2,3,4 to match up with the chuck. If you look at the pic of the jaws carefully you'll see that they look like they've been made on different days in different factories and even at a causal glance are not well matched. So, if that's what a simple thing like chuck jaws are like, imagine what a 3-phase motor and invertor built into a headstock is like.

Although the jaws are offensive to the eye, it's not such a big deal on a woodturning lathe. I've also attached a pic of the lathe bed, which is two sections bolted together. Though when ground, the beds match up, it will be evident that the two castings are offset. I've little doubt that these casting also came from the orient rather than from 'down under'.

Lathe speed controllers seem often to not be up to the task and I think Colin ('Retired') will endorse that from his own experiences. He abandoned the one that had failed on his small Clarke lathe and fitted an industrial sewing machine and controller which I've seen in action - it works a treat.

I think more and more companies are coming to realise that if they cheapen their production costs by shifting production to the far east, they cheapen their name, lose their reputation for quality, and lose out to the competition. Basically, they forget what made them successful in the first place - quality products. I feel safer in a plane with Rolls Royce engines made in Derby than if they were outsourced to China, India or wherever.

Ooops - drifting again!

[ed731pdh]

The only company I've known of in the past that does this sort of thing is a company called Transwave, who incidentally appear to have a store on ebay these days: http://stores.ebay.co.uk/TRANSWAVE-Converters

[pwdrive]

The only company I've known of in the past that does this sort of thing is a company called Transwave, who incidentally appear to have a store on ebay these days: http://stores.ebay.co.uk/TRANSWAVE-Converters

I had a Transwave down at the sawmill, it worked no problem.

Lawrence.

[John M0GLN]

I converted both my Myford Super 7 and Meddings Pillar drill to 3 phase with invertors, both have 0.5 HP motors and the Myford has a Jaguar invertor and the Meddings a Hitachi, both are brilliant, to be able to drill a hole at say 1000rpm and then countersink at 25rpm without belt changes is just so much easier and also screw cutting on the Myford, I can screw at quite high speed and then quickly slow right down and stop at a shoulder. I know that the motor fan cooling won't be much good at slow speeds but depending on your needs it might not matter, I've never had any problems over the last 10 years.

Regards

John

[ex 2 Base]

As Jeffrey says its not YET possible to have speed control via an inverter using a single phase motor. Single phase multi speed, pole changing motors are rare and expensive. I suggest you get an inverter and a 3 phase motor,the change over is not difficultI have an inverters on my mill,drill and lathe all pre owned as the car sales man says, bought from David's and Colin's monthly meeting place, Rufforth several years ago. Secondhand three phase motors are available, no need to buy new ones as so many dealers says. Three phase motors are smoother running, cheaper the single phase and are more reliable. No burnt out start windings or faulty switches with them. Ted

[Retired]

Hi,

Good luck Dennis; whatever you decide it's going to hurt your pocket.

Many thanks David for the mention; yes I've recently converted my Clarke lathe it now being fitted with a countershaft and variable speed Servo motor costing around £200 in total.

http://golbornevintageradio.org/forum/sh...p?tid=2861&page=14

I've also bought a VFD (variable frequency drive) through eBay at around £75 for my woodturning Jubilee lathe and converted to 3 phase motor; I've had the lathe running but I want to fit a clutch because I don't like to stress any motor with constant start/stop cycles this is very important with a cap start single phase motor; I had a 1.5hp single phase motor expire in a cloud of smoke whilst cutting cast iron gears but I was cutting a tooth each minute.

Lawrence liked his Transwave converter and I can appreciate this because the Transwave worked well in Lawrence's situation. I disliked my 7.5hp Transwave so much I sold both my Colchester and huge Dominion lathes as the transwave wound up the key in my back. I found my Transwave converter to be very poor at starting under load so much so that I returned mine to Transwave to have it checked and serviced but it was declared in good order?

My Transwave was for 3 phase motors but you say your motors are single phase Dennis. A Transwave converter is expensive and you would still need to change the motors to 3 phase?

On Practical Machinist forum most members are simply going the VFD route with 3 phase motors which is straightforward enough; swap the motor and hook up the VFD and the machine is running. The problem with a VFD is it needs to be kept clean away from dust so it's possible to remotely mount the VFD and run a couple of controls to the machine; start/stop and pot for speed control. I haven't reached this stage yet because I hope to also fit a clutch to the Jubilee.

Regarding the Clarke I burnt out the control board and DC motor by expecting the lathe to cut metal not scratch metal; a new control board would have cost around £130 then a new motor would have also been required; I had no intention of bringing the lathe back to original spec knowing I would be constantly blowing it up so I decided to upgrade to a larger motor and found an industrial sewing machine Servo motor suited my needs perfectly.

As David kindly states it works a treat but once I start to use the lathe in anger I won't be soft with it and if I find the motor overheats (thermal protected) I can now change the pulley sizes to allow the motor to run at a higher speed providing better cooling alternatively I could also mount a fan to provide additional cooling. When I worked at Brook Motors we sold many FVU's (forced vent units) these were fans mounted into an extend fan cover and the cover was a direct replacement only needing the fan wiring up; we also supplied many motors already fitted with the FVU and these ensured the motor ran cool at low revs when coupled to a speed controller.

Trying to modify an existing drive can be interesting but time consuming with costs involved.

It all depends how far you want to go Dennis and how much money and time you want to put in.

My first choice would be to install 3 phase with a second choice being the VFD. I installed my own 3 phase for at the time under £120 and it will easily cope with 10HP.

http://unique3phase.com/

Had I been aware Doug's unique3phase instructions were available I would still have my big lathes. Doug's Unique3phase transformer method is just brilliant; once the transformer is wound and each machines motor phase balanced to the transformer it is then just like having normal 3 phase laid in. My 3 phase has now been in use a few years and gets regular use; it provides full power full time unlike a Transwave converter.

Kind regards, Col.