3-phase inverter

rock22

Hi, not sure if this is the right place to post this.
I recently purchase a garage machine with a 3-phase, 2-speed motor of 0.8/1.1 kW. I only have single phase at my home and want to adopt it to run here. The machine is belt driven from the motor. Separately, there is also a small 3-phase motor which pumps coolant through the machine and is also needed.

I am thinking of either getting a 3-phase inverter or replacing the motors with single phase motors.

I have been told that 3-phase inverter will only operate one motor and that therefore I will need 2 inverters. I have also been told that the motor often will not work as smooth as it did on 3-phase.

On the other hand , I have been told that a single phase motor will not be as smooth. It will also be only single speed.

Just wondering which is the best option
A, use inverter(s) and retain current motors
B, fit single phase motors.

Thanks for your help and advice.

PS I would also appreciate links to suppliers if that is permitted on Boards.

ShamFeen

Have you considered getting a generator? I know a lot of people who run whole plants from them. I'm sure you could get one cheap second hand or even in the short term hire one.

seaniefr

An inverter taking 220vac and outputting to a three phase motor would be fine for what you need you would probably need 2 though as you can use it to vary speed of the belt drive. It would be easier to retro fit an inverter than change motors and all the messing that would go with that. Anyone that supplies Control techniques (Emerson electric I believe they are called now) would probably be fine. There was a bunch on eBay based in nottingham I think can't remember what they were called but the key to all this is sizing the inverter to the job at hand in other words go a little bigger on the inverter side if you can. I have used the Emerson ones on disabled access passenger lifts where it was moved from one site to another and the second site did not have 3 phase. Also some of those inverters will actually run 2 motors together if full output is required in both it really depends what you are using them for. The supplier could tell you more.

SpaceTime

It's a shame ESB Networks charge so much for 3 phase connections. They're pretty common on the continent.

rock22

seaniefr wrote: »

An inverter taking 220vac and outputting to a three phase motor would be fine for what you need you would probably need 2 though as you can use it to vary speed of the belt drive. It would be easier to retro fit an inverter than change motors and all the messing that would go with that. Anyone that supplies Control techniques (Emerson electric I believe they are called now) would probably be fine. There was a bunch on eBay based in nottingham I think can't remember what they were called but the key to all this is sizing the inverter to the job at hand in other words go a little bigger on the inverter side if you can. I have used the Emerson ones on disabled access passenger lifts where it was moved from one site to another and the second site did not have 3 phase. Also some of those inverters will actually run 2 motors together if full output is required in both it really depends what you are using them for. The supplier could tell you more.

Thanks Seaniefr,
I will look them up. Two quick questions if you can answer
1, Does the motor work as "well" on the inverter? (i had that motors are often not as smooth running with inverters - I don't know of this is true.)
2, Can a single inverter manage two motors? - assuming it matches or exceeds power levels. This machine also has a small pump which is also 3-phase but no more than 1/4 hp.

thanks for your time

seaniefr

rock22 wrote: »

Thanks Seaniefr,
I will look them up. Two quick questions if you can answer
1, Does the motor work as "well" on the inverter? (i had that motors are often not as smooth running with inverters - I don't know of this is true.)
2, Can a single inverter manage two motors? - assuming it matches or exceeds power levels. This machine also has a small pump which is also 3-phase but no more than 1/4 hp.

thanks for your time

Hi
1) I have never had that issue - I can only guess that it came about through some mechanical problem with the motor, maybe the age of it or the insulation class or just down the the ability of the person to either not size it right or not set it up right or possibly an inferior inverter manufacturer.
2) it can be done - some manufacturers will facilitate this but for issues like motor protection where you might have an issue with one motor and it might blow the inverter - you would be better off with 2. As far as I can remember it is really only for light duty operations. Again it would be down to the person setting this up for you but for the motor sizing you quoted the inverter size would be small. One point- when going to a supplier you will have to give them all the figures off the motor data plate and the work the motor actually does - the only mitigating factors when sizing are to know when the motor comes under pressure - or on load to size adequately for this.

rock22

Thanks Seaniefr. Appreciate all your help and advice.

2011

seaniefr wrote: »

1) I have never had that issue

+1
Neither have I.
My situation is a little different though in terms of I always have a 3 phase supply.
I generally use ABB ACS550 VSDs.
They are not cheap by any stretch, but I can confirm that the motors run "silky smooth".
Lots of other advantages too such as soft starting. .

you would be better off with 2.

Agreed, but naturally this will push the cost up considerably.
Each frequency drive can be set up to match the exact characteristics of the motor that it is supplying and provide soft start for it.

Bruthal

It's the idler motor type which might not be as smooth as a 3 phase supply.

A VSD type one will be perfectly smooth.

rock22

I have now been told by my local electrical shop that the motor is too old to run on inverter and that I will need both a new motor and an inverter. the plate on the motor is below. ( note it is a 2 speed motor but I will probably only need one speed)



I am not sure if that makes sense as i was originally told I could buy an inverter for it for about €300.

I am now inclined to go for a single phase motor like this. http://www.ebay.ie/itm/200688676785?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649

Would anyone know if that motor be suitable?
Thanks

2011

Perhaps I am missing something, but I can't see how a motor could be "too old" to work with an inverter.

Once the motor gets 3 phases at 50Hz at the correct voltage in the form of smooth sine waves what difference will it make if it is from an inverter or not?

Can you ask you electrical shop to explain exactly what the issue is?

VSDs use Pulse Width Modulation (PWM) to generate a sine wave. High quality VSDs (such as the ABB units) output perfect sine waves thanks to lots of "smoothing" following PWM. Lower quality VSDs output a wave that is much more square and jagged. This can cause heating issues with the motor and can also cause premature bearing failure. These issues can be diminished by de-rating the motor. This is the only issue that I can see, but this has nothing to do with the age of the motor.

I went to the Titanic exhibition in Belfast last year and read the motor spec for the HVAC system. This impressed on me that the design of the squirrel cage 3 phase motors had not really changed since.

Bruthal

Yea can't see age making a difference either.

Voltage possibly might though. Single phase to 3 phase vsd puts out 3 phase 230v probably.

If the motor in machine is 380 in Delta I.e. 380 volt windings, then 380/400 3 phase needed.

2011

Two interesting links here:

http://www.finewoodworking.com/workshop/qa/three-phase-machines-in-shop.aspx

http://www.tortech.com.au/3-three-phase-converter-transormer/single-to-3-phase-converter

2011

Bruthal wrote: »

Voltage possibly might though. Single phase to 3 phase vsd puts out 3 phase 230v probably.

Generally yes it would be a 230V 3 phase output.

If the motor in machine is 380 in Delta I.e. 380 volt windings, then 380/400 3 phase needed.

Good point, the OP needs to check if the motor is connected in Y or D.

seaniefr

2011 wrote: »

Generally yes it would be a 230V 3 phase output.



Good point, the OP needs to check if the motor is connected in Y or D.

Open the motor terminal block on both motors and post a pic of what is inside

iopener

Have tried electro motors in glasniven industrial estate, a fella I know had a 3phase submersible pump with only a single phase supply the fella in electro wired in a couple of big capacitors to create the necessary phase shift to get the pump running. If you take the motor out to him it would be well worth your while

Bruthal

iopener wrote: »

Have tried electro motors in glasniven industrial estate, a fella I know had a 3phase submersible pump with only a single phase supply the fella in electro wired in a couple of big capacitors to create the necessary phase shift to get the pump running. If you take the motor out to him it would be well worth your while

I seen that method used years ago alright. Its probably questionable if it will work in this case though.

rock22

I will take a photo of the connections and will post here. If it helps, the motor was working in a factory connected to 3-phase power. Is the standard 3-phase power connection 220 V or 380 V ?

I will post the photo as soon as I can take it .

Thanks again for everyone taking time to reply.

Bruthal

It's 400v standard. But a motor with 230v windings can connect to 3 phase 230v or 400v depending on connecting it's windings in delta or star.

If it's 380/400 windings, then it needs the 400 volts to operate at it's rated power output.

rock22

The motor plate states that it uses 380V.
I have found that the machine switches between star and delta wiring to change speed. I assume this complicates things.
This is a photo of the motor wiring, but because of the machine switches, i don't think it will be of any help.


I am beginning to think that fitting a single phase motor, with a suitable size pulley, would be the easier route. The motor is on a milling machine and it will be only used occasionally and for small pieces of work - it will not be used with large cutters or with high speed drive.

Thanks again to everyone for all the help. I have certainly learned a lot about electrical motors!

2011

The star delta starter starts in star (Y) then switches to delta( D).
This is because when the motor is connected in Y it draws a lower starting current than D. The current is in fact reduced by a factor of root 3. The issue is that the power output (or torque) of the motor is also reduced by a factor of root 3. Once the motor has been running a timer switches the connection to D. As the motor is rotating the current does not increase as dramatically as it would if it was simply started in D.

This motor is designed so that 380V will be connected across each winding when running in D configuration.

Your problem is that any single to 3 phase VSD that you are likely to find will most likely output 3 phase at 230V, not 380 (or 400). Therefore the motor in Y and D output will be reduced by a factor root 3.

I was hoping that your motor was only connected in Y at 380V. That way if it was connected in D at 230V the output would have been equivalent.

Bruthal

I'd say the output factor is 3 rather than root 3 probably. I could be wrong though.

2011

Bruthal wrote: »

I'd say the output factor is 3 rather than root 3 probably. I could be wrong though.

Yes, you are correct.
My bad.

Bruthal

2011 wrote: »

Yes, you are correct.
My bad.

Ye had me wondering there for a few minutes. I thought I'm definitely losing it.

Hoagy

It probably makes no difference at this stage,

but that's unlikely to be a star delta starter, more likely a 380v 2 speed delta wye/wye as below.
Connecting all six terminals to a delta supply would not be recommended.

These pages are from the 'little red bible', does anyone remember it?

Bruthal

Yea a motor wont really be any slower in star than delta, except for slightly more slip in star especially when loaded.

rock22

Thanks again for all the help. I'm really learning more and more.

The motor was recently connected to 3-phase power in a workshop. However , it had previously been run from a solid state inverter. This was about 20 yrs ago. I believe that the motor and machine is about 50-60 yrs old.

It has a switch which changes speed from 1400 to 700 rpm. This seems to switch from star to delta ( or the other way round - I am not too sure). For my uses I would be quite happy to get one speed working as the machine has an internal gearbox giving another 6 speeds. Using appropriate pulley size I am sure I can find acceptable speed range.

Just wondering if this is a possibility for me - to leave in in delta configuration always?
http://www.model-engineer.co.uk/forums/postings.asp?th=65641

I understood that 3-phase supply was 380 V. Is there also a 240V 3-phase supply? Why would one need a 240V 3-phase supply?

Again , I would really like to thank everyone for all the time on this. I intend going back to the local shop who originally said they could supply an inverter but are now saying that I need a new motor as well.

Hoagy

rock22 wrote: »

It has a switch which changes speed from 1400 to 700 rpm. This seems to switch from star to delta ( or the other way round - I am not too sure)

Low speed would be in delta - but with only three terminals connected

High speed would be in star.

It can be permanently connected in either speed, with an appropriate overload protection. ( a star-delta starter is not suitable)

rock22 wrote: »

I understood that 3-phase supply was 380 V. Is there also a 240V 3-phase supply? Why would one need a 240V 3-phase supply?

Continental Europe had 220v three phase. We used to see a lot of dual voltage motors here which would be stamped 220/380volt. Yours is 380volt only.

I would think that your simplest solution to this is to fit a new single phase motor.

2011

Hoagy wrote: »

It can be permanently connected in either speed, with an appropriate overload protection. ( a star-delta starter is not suitable)

If your drawing reflects the situation (most likely it does).

Continental Europe had 220v three phase. We used to see a lot of dual voltage motors here which would be stamped 220/380volt. Yours is 380volt only.

Yes, but this has changed. For electricity supplied at Low Voltage by ESB Networks, the nominal standard is 230/400 Volts, 50Hz.

See link:
http://www.esb.ie/esbnetworks/en/about-us/faqs.jsp

I would think that your simplest solution to this is to fit a new single phase motor.

You may well be right.

However it would be no harm to see what it would cost to have a three phase supply installed. This can be a very expensive exercise, but that depends on a number of factors. You might just be lucky. This would solve all of your problem and provide you with the other advantages of having three phase - just a thought.

seaniefr

Hoagy wrote: »

Low speed would be in delta - but with only three terminals connected

High speed would be in star.

It can be permanently connected in either speed, with an appropriate overload protection. ( a star-delta starter is not suitable)



Continental Europe had 220v three phase. We used to see a lot of dual voltage motors here which would be stamped 220/380volt. Yours is 380volt only.

I would think that your simplest solution to this is to fit a new single phase motor.

Yep unfortunately in this case looking at your photo the other end of the low and high speed motor windings are joined inside the motor so any manipulation or changing etc. from delta to star or vice versa is impossible but I would still check with the shop

2011

By the way the cables are not terminated very well.
A few lugs would be an idea.