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Mill motor

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kevin large21/10/2017 10:57:27
105 forum posts
9 photos
My mill motor says on the plate 1 hp 120-240 volt
1 phase
Can I fit a vfd to this
Andrew Tinsley21/10/2017 11:03:57
578 forum posts

Look on the plate and see if it says 1 P(hase) or £3 P(hase). If it says 3 Phase then you can probably fit a VFD if 1 Phase then you can still fit a VFD, but these are rare beasts and probably expensive. Better to swop the motor for a 3 phase one and then you will have lots of VFDs to choose from.

Interesting that the motor appears to be dual voltage, not all that common in single phase motors. I presume you change the voltage by connecting to a different terminal in the connection box?

Andrew.

Tim Stevens21/10/2017 12:23:11
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698 forum posts

I wonder if it is a DC motor, and the 'dual voltage' is the range of voltage giving variable speeds?

A DC motor is likely to have brushes, in holders towards one end of the cylindrical case. Might be at right angles or opposite. In this case, there will also be a speed knob on the control box, and some electronics too.

A DC motor will not work on AC, so it also has a rectifier in the electronics, but this rules out your plan to use a Variable Frequency Device.

You don't say what reason you have for the change - so please explain. If your existing motor is playing up, there may be answers which meet your needs without a complete re-design.

Regards, Tim

kevin large21/10/2017 14:17:09
105 forum posts
9 photos
There is nothing wrong with the motor I just thought It would be easier to vary the speeds rather than moving belts
Howard Lewis21/10/2017 15:41:48
921 forum posts

My lathe was fitted with VFD before delivery, and it is very handy (Really am almost too idle to change belts) BUT

Reducing the speed this way reduces torque, and the speed of the cooling fan, so the motor could run hot on heavy low speed cuts. You never get something for nothing.

Your three phase motor will probably need to be dual voltage, and have the windings connected in the correct way (Can't remember Star or Delta)

Someone will tell us!

Occasionally, I manage to summon the energy to change belts on the single phase Mill/Drill, to change speeds, so a VFD is a nice to have rather than a necessity.

Howard

Edited By Howard Lewis on 21/10/2017 15:42:12

Ian S C22/10/2017 10:02:04
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6460 forum posts
216 photos

My lathe has a dual voltage single phase motor, 120v, 230v. Changing the wiring around to run on the 120v would not change the speed of the motor, it would only speed up the motors demise, speed on these motors is dependant on the frequency of the AC supply.

Ian S C

John Haine22/10/2017 10:28:43
1559 forum posts
90 photos

Whether it's a DC or induction motor, the key thing the plate says is "1 phase". So no, you can't use it with a VFD. = Variable Frequency Drive.  And if it is a DC motor it probably has a speed controller anyway so you wouldn't need to.

Edited By John Haine on 22/10/2017 10:29:27

Clive Foster22/10/2017 10:48:02
1135 forum posts
19 photos

120 / 240 v single phase motors are quite common on equipment intended for both US and European markets. My old Alpine 4 1/2 " bandsaw has one. Basically all the windings are split in two with a connection in the middle. For 120 volts the two halves are connected in parallel and for 240 volts they are connected in series. So each winding still sees 120 volts whatever way round it is. Start capacitor usually sits in the middle too. All quite clever. Generally less efficient than a proper single voltage unit, the one on my Alpine gas very hot over long periods of use.

Even if you could find one in the UK a single phase VFD device wouldn't work very well on such a motor. If nothing else it will be very unhappy with the start capacitor.

Clive.

Michael Gilligan22/10/2017 10:53:43
10219 forum posts
443 photos
Posted by John Haine on 22/10/2017 10:28:43:

... induction motor, the key thing the plate says is "1 phase". So no, you can't use it with a VFD. = Variable Frequency Drive.

.

Really ?

**LINK**

http://www.invertekdrives.com/variable-speed-drives/optidrive-e2-single-phase/

MichaelG.

kevin large22/10/2017 11:19:45
105 forum posts
9 photos
Ok thanks every one
So next question is
What sort of 1hp motor do I get ie 2 pole 4 pole and what speed
Clive Foster22/10/2017 11:26:07
1135 forum posts
19 photos

Interesting link Michael.

But it looks to be a somewhat limited device.

Page suggests its intended primarily to reduce wasted power consumption in pumps and similar when running below their rated load. Non-reciprocating pumps and fans tend to have a very rapid delivery / power consumption drop off when speed falls so the actual speed range variation needed in practice to match power to load probably isn't great. Also says conveyor systems. I imagine motors on such are inefficient when running lightly loaded so a VFD could well manage power consumption better than the motor does itself at low loads. There is a lot of literature on this sort of thing concerning 3 phase VFD applications.

Shaded pole motors tend to have pretty horrible power efficiency at the best of times so almost anything is going to be an improvement. Despite efficiency being even worse when running at other than the rated speed you could still end up using less energy overall.

Surprised that split phase capacitor run motors are recommended as, naively, the permanent capacitor would be expected to make it very frequency sensitive.

Clive.

Clive Foster22/10/2017 11:51:46
1135 forum posts
19 photos

Generally for machine tool use you are better off with lower basic motor speed, 4 or even 6 pole rather than 2.

Output torque of a VFD controlled motor drops off in rough proportion to how far the speed is varied from its nominal nameplate rating. Any decent VFD will have some degree of torque boosting capability to considerably counteract the inherent drop off for smaller speed variations which helps. On machine tools you almost invariably need more torque at lower speeds to cope with larger jobs or cutters so any serious drop off in torque or power will be noticeable. Higher speeds being usually reserved for small cutters and jobs which don't need so much oomph so torque and power drop off probably won't affect you.

VFD's aren't a universal panacea. As a general rule with any reasonably modern, reasonably efficient, motor the satisfactory "just fit and use" working range is about ± 1/3 rd of the nominal speed. That is around 35 to 65 Hz on 50 Hz motors, perhaps a bit more or a bit less depending on the exact installation. Outside that range torque and output power variation is generally large enough that you need to do a bit of engineering to decide how much power you need. Commercial installations often use very large motors to get sufficient torque at lower speeds. Something we should be careful of copying as the power available at normal motor speeds will be very much more than the machine was designed for and potentially dangerous.

My view is that a VFD on our sizes of machine is an excellent speed range filler in. So if you have three speeds on the belt setting to middle speed and using a VFD covers the whole range, and bit more just fine. Dropping to lower speed belt settings gives an extended low speed range. Great on lathes when screwcutting. Not much power needed so you can seriously slow down bottom direct drive speed for a nice quiet job without intrusively ringing backgears.

Clive.

Edited By Clive Foster on 22/10/2017 11:52:20

Edited By Clive Foster on 22/10/2017 12:31:00

Andrew Tinsley22/10/2017 12:08:15
578 forum posts

Single phase VDFs do exist and operate in exactly the same way as a 3 phase VDF. There is no theoretical or practical reason for them not to work!

The problem is finding one at a reasonable price, They are a rare bird, as there is little call for them. That they exist is not in doubt. In fact I have one that I use on a single phase Parvalux induction motor. It is an old device and it appears to have been made by ABB, at least that is the name on it.

It isn't the greatest of VDFs as the speed stability is a bit dodgy. I found it in the scrap bin when I was working for a large company, so that might be the reason for the poorish speed stability, i.e. it has a fault.

Andrew.

Michael Gilligan22/10/2017 12:23:39
10219 forum posts
443 photos
Posted by Clive Foster on 22/10/2017 11:26:07:

Interesting link Michael.

But it looks to be a somewhat limited device.

.

Fully accepted, Clive ... and thanks for the very useful notes that followed

It was just that I thought John's statement to be a rather sweeping generalisation, and I couldn't really see the logic; so felt obliged to check.

MichaelG.

Clive Foster22/10/2017 13:07:18
1135 forum posts
19 photos

Andrew

I think the major issue against single phase VFD devices is start up problems. Can't have anything with a centrifugal switch on the start winding as it will drop in if slowed down too far. I suppose you could bypass the switch but that makes installation more complex and driving the start winding isn't going to be trivial as driver characteristics need to be somewhat matched to the motor. Especially when starting and running at low speeds. All do-able but makes for a complex device. Especially before cheap micro-controllers.

Realistically connect and play is limited to shaded pole and permanent split capacitor motors. Which aren't the most common of devices as the inherent characteristics make them unsuitable for general purpose use. So, unlike the 3 phase VFD situation, there is no vast installed base of standard technology that could happily adopt an electronic speed control system in place of, or additional to, standard mechanical methods.

If you are going to have to change motors might just as well get a standard 3 phase and be done with it. Probably cheaper to although the low powers normally associated with shaded pole motors aren't generally available. But DC motors are common at such low powers and generally much better at the variable speed bit than any shaded pole motor can be. Primary advantage of shaded pole motors is that they are a relatively cheap, simply plug into the mains, device for low powers. Putting a VFD control box in front of it pretty much wipes out any possible cost advantage over a DC motor so a very compelling reason is needed to use a VFD.

My guess is that Andrews motor was part of a system made for use in explosive, or explosive risk, atmospheres. Commutator sparks from ordinary DC motors not being desirable in such situations and truly gas tight motors very expensive.

Clive.

Neil Wyatt22/10/2017 14:22:55
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Moderator
11669 forum posts
532 photos
63 articles
Posted by Michael Gilligan on 22/10/2017 10:53:43:
Posted by John Haine on 22/10/2017 10:28:43:

... induction motor, the key thing the plate says is "1 phase". So no, you can't use it with a VFD. = Variable Frequency Drive.

.

Really ?

**LINK**

http://www.invertekdrives.com/variable-speed-drives/optidrive-e2-single-phase/

MichaelG.

"especially fans and pumps which typically do not require high starting torque"

Andrew Tinsley22/10/2017 15:10:12
578 forum posts

Hello Clive,

I am not advocating single phase VFDs, quite the contrary! if you look at my initial response, I strongly recommended changing motors to a 3 phase unit and using an ordinary single phase to three phase inverter!

John Haine, said that you can't use an inverter on a single phase motor. I was just pointing out that there are inverters which will drive a single phase motor. My ABB inverter isn't particularly good at starting under much load and does appear to have a fault, as the set speed varies somewhat. So they do exist, but really NOT recommended!

Andrew.

John Haine22/10/2017 16:07:20
1559 forum posts
90 photos

OK, OK a bit of a generalisation. Obviously you could feed a single-phase induction motor from a variable frequency if you had a suitable drive, but actually even "single phase" motors have to have some way to generate a phase shift at least to start. Hence capacitor start or start and run motors, that have an extra winding displaced rotationally to form in effect a 2-phase motor. As pointed out these drives are really for things like fans that don't need high starting torque.

Back to Kevin's 2nd question. You need to look at what the rated speed of the present motor is, it will probably be ~2800 or ~1400 rpm on 50 Hz. This will correspond to 2 pole and 4 pole respectively. Whichever it is, get a 3-phase unit with that number of poles/rated speed.

Michael Gilligan22/10/2017 16:41:17
10219 forum posts
443 photos
Posted by Neil Wyatt on 22/10/2017 14:22:55:

"especially fans and pumps which typically do not require high starting torque"

.

Neil,

My response to Clive refers

MichaelG.

kevin large23/10/2017 14:06:21
105 forum posts
9 photos
Can I use a 1 hp motor with a 2hp vfd

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