Motor query.

kadman

Can I buy a 3 hp single phase motor dual speed 1400/2800 to replace the 3 phase one in a woodturning lathe I have . The existing one is a dual speed, and I need that facility.

I,ve been told a rotary convertor is an option, but thats 750 sterling + vat.

Any advice would be welcome

kadman

2011

kadman wrote: »

Can I buy a 3 hp single phase motor dual speed 1400/2800 to replace the 3 phase one in a woodturning lathe I have . The existing one is a dual speed, and I need that facility.

I,ve been told a rotary convertor is an option, but thats 750 sterling + vat.

Any advice would be welcome

kadman

3hp is about 2.2kW

3 phase is always best for a number of reasons. Is 3 phase definitley not an option for you?

I would think that rotary convertors have gone out with the Indians. Perhaps the advice was to go for a VSD (variable speed drive). This could take a single phase supply and output 3 phase to your motor. A VSD would give very percise speed control from almost stopped to the maximum speed that the motor is capable of. But needless to say they are not cheap.

kadman

2011 wrote: »

3hp is about 2.2kW

3 phase is always best for a number of reasons. Is 3 phase definitley not an option for you?

I would think that rotary convertors have gone out with the Indians. Perhaps the advice was to go for a VSD (variable speed drive). This could take a single phase supply and output 3 phase to your motor. A VSD would give very percise speed control from almost stopped to the maximum speed that the motor is capable of. But needless to say they are not cheap.

I am quite happy to use the 3 phase motor in the machine, if I can run it off single phase supply.I,ve been told by a UK company that as my motor is a pole change 2 speed, the only retrofit option is a rotory convertor.

Thats why I was wondering is there a compatible 3hp single phase option.

kadman

2011

kadman wrote: »

I am quite happy to use the 3 phase motor in the machine, if I can run it off single phase supply.

Like I say you can with a VSD, but I won't be cheap.

I,ve been told by a UK company that as my motor is a pole change 2 speed, the only retrofit option is a rotory convertor.

Interesting, I have never seen a rotary convertor. I just heard about them being used in the distant past.

The synchronous speed of a motor can be altered if the number of poles can be changed. The synchronous speed is the speed that the rotating magnetic field in the stator windings rotates at. The rotor on induction motors will rotate at a slightly slower speed.


synchronous speed (rpm) = (120 x Frequency)/Number of pole pairs

In Ireland the frequency is 50Hz

kadman

2011 wrote: »

Like I say you can with a VSD, but I won't be cheap.



Interesting, I have never seen a rotary convertor. I just heard about them being used in the distant past.

The synchronous speed of a motor can be altered if the number of poles can be changed. The synchronous speed is the speed that the rotating magnetic field in the stator windings rotates at. The rotor on induction motors will rotate at a slightly slower speed.


synchronous speed (rpm) = (120 x Frequency)/Number of pole pairs

In Ireland the frequency is 50Hz

The company in England say that the only option for my particular motor is a rotory convertor. I dont know why, I,m not a sparks.

If I want a VSD package, I will have to ditch the motor I have , and buy a new one as supplied with the package. I dont know whether this is a sales pitch or not.

Here,s the spec of my 3 phase motor,



kadman

Bruthal

Its probably an idler motor converter they are talking about, rather than the rectifier rotary converter device from decades ago. The idler converter generates a third phase from one of the 3 phase connections of a 3 phase motor which is run from L and N connected to the other 2.

A VSD is a better job for your application.

A 3 hp (2.2kw) induction motor would be very inefficient as a single phase one, so probably would`t be too common.

kadman

robbie7730 wrote: »

Its probably an idler motor converter they are talking about, rather than the rectifier rotary converter device from decades ago. The idler converter generates a third phase from one of the 3 phase connections of a 3 phase motor which is run from L and N connected to the other 2.

A VSD is a better job for your application.

A 3 hp (2.2kw) induction motor would be very inefficient as a single phase one, so probably would`t be too common.

1. Will my existing motor work with VSD switching, and if not, why not.

2. Are dual speed 3hp single phase 1425/2850 motors , available. to buy.
thanks

kadman

Bruthal

kadman wrote: »

1. Will my existing motor work with VSD switching, and if not, why not.

There is no reason i can think of as to why it wont work with a VSD.

The idler motor converter which i assume the UK company were talking about, does partly the same thing as a single phase to 3 phase VSD (single to 3 phase conversion), but much more crudely. The VSD can vary the frequency as well, so you could have much more speed control than just the 2 speeds.

2. Are dual speed 3hp single phase 1425/2850 motors , available. to buy.
thanks

I wouldnt say it would be easy to get a single phase induction motor of that size with dual speed (4 pole). Single phase induction motors just dont have much torque as the magnetic field just swaps from opposite sides rather than in a 3 point triangular fashion like a 3 phase one does, so single phase ones are only usually used in small applications.

2011

robbie7730 wrote: »

Its probably an idler motor converter they are talking about, rather than the rectifier rotary converter device from decades ago.

+1

The idler converter generates a third phase from one of the 3 phase connections of a 3 phase motor which is run from L and N connected to the other 2.

I have never come across these.

Modern plants generally go for VSDs nowadays. VSDs give fantastic speed control, overload protection, effeciency and power factor. All at a price....

A VSD is a better job for your application.

A 3 hp (2.2kw) induction motor would be very inefficient as a single phase one, so probably would`t be too common.

+1

Bruthal

2011 wrote: »

I have never come across these.

Modern plants generally go for VSDs nowadays. VSDs give fantastic speed control, overload protection, effeciency and power factor. All at a price....

I have installed one just the once about 4 years ago. They do work, the motor actually generates the 3rd phase, but they are a crude way of doing it compared to a VSD.

The 3 phase from it would be 230v 3 phase, but the unit i installed had a step up transformer to give the 400v.

Capacitors are needed to balance the generated phase so its central between the L and N depending on the load, and the capacitors would need to be changed if the load changed much, within the load capacity of the converter.

A VSD is the way forward in this case id say.

kadman

Thanks for all the info, very much appreciated.

General consesus seems to suggest a VSD as a solution,

But,

The uk company says it is not an option with my existing motor, as described in their e mail to me. For obvious financial reasons, I,d like to use my existing if I can, but they say otherwise.

Hi XXX

The motor is pole-change 2-speed 1400/2800rpm

The only “retrofit” option is a rotary converter rated at 3kW/4hp. Cost from £610 + VAT ex-Birmingham

However, if you were prepared to change the motor to a single speed 2800rpm 3hp motor (subject to dimensional compatibility), you could then consider a variable speed drive package including the new motor which would cost from £410 + VAT ex-Birmingham.

This would transform the performance of the lathe by introducing electronic variable speed and would easily replicate the 1400rpm motor shaft speed and all other speeds between 1400rpm and 2800rpm.

The 2800rpm motor at 2.2kW/3hp would be housed in a 90L1 frame (specification attached) with a 24mm x 50mm shaft dimension.

I have attached some details for your consideration and welcome your further comments.

Bruthal

kadman wrote: »

Thanks for all the info, very much appreciated.

General consesus seems to suggest a VSD as a solution,

But,

The uk company says it is not an option with my existing motor, as described in their e mail to me. For obvious financial reasons, I,d like to use my existing if I can, but they say otherwise.

Well i would be interested myself to know why they say a VSD wont run your 3 phase motor.

Them pole change 3 phase 2 speed motors are just duplicating the poles so the motor only needs to turn 60 degrees instead of 120 degrees to reach the next pole, so it takes twice as long to turn. I cant see how a VSD would have a problem running it.

Can you 2011?

kadman

robbie7730 wrote: »

Well i would be interested myself to know why they say a VSD wont run your 3 phase motor.

Them pole change 3 phase 2 speed motors are just duplicating the poles so the motor only needs to turn 60 degrees instead of 120 degrees to reach the next pole, so it takes twice as long to turn. I cant see how a VSD would have a problem running it.

Can you 2011?

Just got this clarification from the uk company. Can I get a VSD for a single phase motor guys.



Hi XXX

The existing motor can only be configured for 400-415v so is incompatible with the output of a standard single-phase input VSD.

The output from a single-phase input VSD is 3-phase 220-240v not 3-phase 400-415v, hence the recommendation to change the motor to a compatible motor.

I hope this clarifies things

Bruthal

kadman wrote: »

Just got this clarification from the uk company. Can I get a VSD for a single phase motor guys.



Hi XXX

The existing motor can only be configured for 400-415v so is incompatible with the output of a standard single-phase input VSD.

The output from a single-phase input VSD is 3-phase 220-240v not 3-phase 400-415v, hence the recommendation to change the motor to a compatible motor.

I hope this clarifies things

If thats the case, i think you would be better getting a 3 phase VSD and suitable 3 phase motor with 230v windings. When connected in delta they will be getting 230v on the windings then. They can be connected in star to 400v as well, but that wont apply here.

The rotary convertor i once installed had a step up transformer for the same reason, to get the 230v 3 phase, up to 400v 3 phase.

2011

robbie7730 wrote: »

Well i would be interested myself to know why they say a VSD wont run your 3 phase motor.

Them pole change 3 phase 2 speed motors are just duplicating the poles so the motor only needs to turn 60 degrees instead of 120 degrees to reach the next pole, so it takes twice as long to turn. I cant see how a VSD would have a problem running it.

Can you 2011?

Interseting.

Here is a link to a single phase ABB VSD:

http://www.midwestequipment.com/single-phase-200240vacvariable-frequency-drive-p-751.html

Granted, it provides a 3 phase 230VAC supply.

All the VSDs I have installed have a 3 phase supply. I always knew that they could be run on single phase. I assumed that it would be possible to get a 400VAC 3 phase output from a single phase 230VAC input.
I will find out when I have a chance.

Bruthal

2011 wrote: »

Interseting.



All the VSDs I have installed have a 3 phase supply.

Same here

I always knew that they could be run on single phase. I assumed that it would be possible to get a 400VAC 3 phase output from a single phase 230VAC input.
I will find out when I have a chance.

Again, so did i. As i was saying, the idler convertor i installed had a sinle phase step up transformer in the supply to the idler motor to get 400v 3 phase out.

A single phase to 3 phase VSD would likely need the same, but i was assuming that type of VSD was available.

2011

I talked to ABB today. They sell a VSD that takes a single phase 230VAC input and outputs a 230VAC 3 phase supply.
They do not sell a VSD that take 230VAC single phase input and gives a 400VAC 3 phase output, although they did agree that it was possible and had to check to confirm that they did not sell one.

Most of the small 3 phase motors that we use at work are designed to be star connected to a 3 phase 400VAC supply and delta connected to a 3 phase 230VAC supply.

If the budget stretches to it I would be going for a VSD and suitable 230VAC 3 phase motor.

unit 1

The key thing here is voltage. A vsd alters both frequency and voltage.
They work by converting your supply to dc and then reconverting the dc to the required output. Because of the lower single phase voltage 240 as opposed to 400 then a standard drive cannot generate a suitable dc voltage to create a three phase 400v output.
If you had to run a three phase motor (I worked on an 11kw one recently) on single phase what they do is bypass the first stage of the vsd and supply the dc bus of the vsd with a suitable dc voltage created by converting 240v single phase to 400v single phase.
From the box I looked into this seemed very messy, big and bulky, and slightly scary if something "broke".
I would imagine your best option in the long run would be a vsd and a 240v three phase motor, bearing in mind that the flexibility this would give you.

2011

unit 1 wrote: »

Because of the lower single phase voltage 240 as opposed to 400 then a standard drive cannot generate a suitable dc voltage to create a three phase 400v output.

I don't agree. Remember 400V is the voltage between phases. Each phase is at 230V WRT earth regardless of whether it is single or three phase.

As you can see here voltage is not an issue (it is possible to get 240VAC from just 12VDC using an inverter).

I would imagine your best option in the long run would be a vsd and a 240v three phase motor, bearing in mind that the flexibility this would give you.

Perhaps, I suggested this in my last post.

unit 1

2011 wrote: »

I don't agree. Remember 400V is the voltage between phases. Each phase is at 230V WRT earth regardless of whether it is single or three phase.

As you can see here voltage is not an issue (it is possible to get 240VAC from just 12VDC using an inverter).


Perhaps, I suggested this in my last post.

Just to make my point a bit clearer, you cannot get 400v three phase from a standard drive by supplying it with 240v single phase, without intervening in the middle stage.
240v single phase, to dc, to 400v three phase wont happen. What happens in the unit I used was 240v single phase, stepped up to 400 v single phase to dc (the first stage of the drive, which seemed like an off the shelf,virtually being bypassed ) , then to 400 three phase.
The unit you linked seems to work the following way 12v dc to 12v ac stepped up to 240v ac.
The motor he showed was rated for 380v so in the long run he is probably better off buying a new 240 single phase motor and drive and as others have pointed out the extra flexibility might swing it for him.
BTW vsds seem to vary greatly in price and it seems in complexity so shopping around is the key point to remember.

2011

unit 1 wrote: »

Just to make my point a bit clearer, you cannot get 400v three phase from a standard drive by supplying it with 240v single phase, without intervening in the middle stage.

So what you are saying is theoritically it is possible, but only if the DC voltage is high enough which would require additional components?

The unit you linked seems to work the following way 12v dc to 12v ac stepped up to 240v ac.

Yes, I was just trying to illustrate that it is possible to input a lower voltage and output a higher voltage without using a transformer.

BTW vsds seem to vary greatly in price and it seems in complexity so shopping around is the key point to remember.

+ 1

Bruthal

2011 wrote: »

I don't agree. Remember 400V is the voltage between phases. Each phase is at 230V WRT earth regardless of whether it is single or three phase.

That part wouldnt really have any relevance as such. 230v in needs to be stepped up along the way, with a transformer being likely the simplest, (although using a 230v windings motor is simpler again)

Its 230v between the 2 supply connections to the VSD, so what it is compared to earth or another phase is not really relevant.