Thread: 2hp phase converter up and running!

Here is a direct link to the diagram Bill.

http://aycu16.webshots.com/image/242...0233120_rs.jpg

As you have 16mm2 supply, you probably won't need a pony start system. In this case, you will simply replace the pony motor shown in the diagram with start caps.

Take the run cap sizing shown with a grain of salt. A lot is dependant on the type of motor you have for the idler, as I have just learned from the Practical Machinist site.

Good luck, and please let us know how you get on with it.

Thanks Fossil very much appreciated.

I assume you have delta wound 5HP motor in your circuit. I have been doing quite a bit of reading and can't quite get my head around why you can run a delta strapped 415V motor on 240 for the idler and all the other motors. My 3 phase motors do not have any extra terminals for a second set of 240 windings - just the usual 9 for delta or wye strapping and 415 volt written on the label. 3 phase 415 volt is 415 volt between the three phase terminals and from memory 240 volt from any of these phases to neutral. Please explain?

Thanks

Bill

Originally Posted by Billy Bignutz

Hi guys
I have a big metal lathe running 3HP single phase but would prefer 3 phase for the torque.

Any help greatly appreciated.

Bill

Hi BB,

Correct me if I am wrong but I get the impression from what you said that one can take deeper cuts (on the same feed rate) without stalling?

Cheers
MH

Hi again Bill,

I run all my motors delta 240v.
That is... 240v phase to phase, which is 138v from phase to neutral.

415v is a theoretical voltage, and in essence, all of your 415v 3~ motors will run on 240v at full power. Of course they will draw more current from the 1~ supply, which is why we need good single~ power.

The 4 wires coming from the street to any premises are: Neutral, and three hot wires which are 240v from ~ to ~ but are actually 138v from ~ to N.
To understand this better, draw up a delta.... (an equalateral triangle, where each side represents 240v to scale). Say you make each side of the triangle 240mm (representing 240v). Now mark the exact centre point of the triangle which represents neutral. Scribe a line from the triangle corners to the centre. Now measure from any of the triangles points to the centre N. You will find that it is 138mm (representing 138v).
Now..... Add up the 3 phases..... 3x 138v and tell us what you get.
Of course there is a trig equation that represents this as well, but I prefer to explain with drawing and measuring rather than trig.

If you have an older star wound motor, you will have to do some brain surgery on it to get it to run 240v delta.... ie, remove the rotor from strator, locate the windings star point, cut and extend the wires to the terminal box. When connecting them up to power, you will have to ensure that the windings connections are sequenced so that motor will start.

I would do some more reading up before starting on the project.
Practical machinist, Home shop machinist, lathes.co.uk or many others have the info that needs to be ingested.

Also.... I am not an electrician, and am in no way an expert on this subject. I have just researched the subject material for a couple of years now, and want to share some of the info that I have learnt. I am open to corrections from anyone who would like to chime in here.

Have fun.

Thanks Fossil.
I had a similar understanding, at least of the outcome of 3 phase 415 volt, until I started looking into RPCs. The american delivery system certainly confuses things. My understanding for Oz was 3 phases were generated with each 415 volt to centrepoint of a star and each 120 degrees phase shifted. If you plot the instantaneous voltage between any two of the phase shifted sign waves you get a 240 volt sine wave ie 240 volts between the phase legs which are wired to a house. What threw me in particular was the following thread addressing a UK 3 phase need written by someone who appeared to be pretty well across RPCs.
http://http://www.practicalmachinist...42.html#000001
In this set up they stepped up 240 to 415 single phase then put it across a delta wired idler. I would have thought if you had 415 volts you would have put it across a star wired idler. Anyway thanks for confirming my old beliefs and getting me back on track.

In your diagram the start and run caps for the 5HP idler are a lot smaller than most of the rules of thumb I have come across. Certainly a saving on the recommended 70mfd/HP run caps split roughly 60:40. Also your note about trimming the run caps to get 1.05VAC seems odd - I would have thought trim them to achieve close to 240VAC?.

Thanks again

Bill

Originally Posted by Metal Head

Hi BB,

Correct me if I am wrong but I get the impression from what you said that one can take deeper cuts (on the same feed rate) without stalling?

Cheers
MH

MH
Someone can correct me if I am wrong also but my understanding is greater torque from 3 phase due to the 120 degree phase shift between phases giving you a much greater torque than in effect the 180 degrees between active and neutral of single phase - like a 3 cylinder car vs 1 cylinder (or is that 2) cylinder car - anyway I think that explains it.

In my case I have a very heavy weight old lathe and thicknesser - both will work OK on 3 phase due to the higher starting torque. In both cases a 3HP single phase motor just stalls on startup under load (boy can that dim the lights). My metal lathe has a clutch fortunately which overcomes the problem - start the motor then engage the clutch. My thicknesser runs at present on a honda 9HP motor - boy can that rip up a lot of chips.

Logic would say that if start up torque is greater then certainly if you put a lathe under load then you should get more torque for the HP with 3 phase.

Hope this helps

BB

Hi again Bill.

I just uploaded a rough sketch of the two motor wiring systems, which is to scale. I hope this goes some way to explaining the direct relationship between 415v wye wound motors, and 240v delta wound. It is the same power we are using, just in a different way, and drawing more current out of 1~ than we would from 1 of the 3 phases in a traditional setup.
http://aycu12.webshots.com/image/227...9234205_rs.jpg

Yes you can step up the voltage on the incoming side to 415v. I saw no need for the massive expense of a transformer when it is very easy to wire up any 3~ motor delta, and use 240v for the supply. There are advantages of course in having a 415v system, but not in my case, as I just want to get my motors running which is the case for most of us woodies.

EDIT.....

In your diagram the start and run caps for the 5HP idler are a lot smaller than most of the rules of thumb I have come across. Certainly a saving on the recommended 70mfd/HP run caps split roughly 60:40. Also your note about trimming the run caps to get 1.05VAC seems odd - I would have thought trim them to achieve close to 240VAC

As previously mentioned.... take any quoted cap sizes with a grain of salt. the ROT is very dependant on you setup. 1.05VAC is meant to read 1.05x vac, which equates to 252v max, which is the high point for balancing the other voltages. I haven't seen a phase converter that had 240v accross all three phases.

My camera has been repaired at last, so here are a few piccies of the new phase converter setup. I have used a 5hp motor for the idler, which gives me what I need for the moment. All of the gear that I used will cope with current from a 15hp setup, which is what the system will end up being when I move bush again in the future.

I ended up with getting it tuned to within 1.5% phase to phase, and it runs well within within 5% phase to phase with my biggest load, being 5hp on my table saw. Considering that utility supplied power is meant to be within 5% of quoted, I am very happy with the setup.

Anyway.... here are the piccies.

http://www.woodworkforums.ubeaut.com...1&d=1191288705

http://www.woodworkforums.ubeaut.com...1&d=1191288819

http://www.woodworkforums.ubeaut.com...1&d=1191288819

http://www.woodworkforums.ubeaut.com...1&d=1191288819

Hi Fossil

Nicely done - very tidy. Congratulations.

I have been a bit slack on this I am afraid. Also unfortunately I haven't come accross an appropriate 3 phase motor at the right price up here yet and also distracted by the purchase of a 2nd hand Lucas mill to which I added a home built slabbing bar. Now building yet another shed for storing my recently cut timber in. Dam the projects keep backing up!!!

BB

Originally Posted by Fossil

Hi again Bill,

I run all my motors delta 240v.
That is... 240v phase to phase, which is 138v from phase to neutral.

415v is a theoretical voltage, and in essence, all of your 415v 3~ motors will run on 240v at full power. Of course they will draw more current from the 1~ supply, which is why we need good single~ power.

The 4 wires coming from the street to any premises are: Neutral, and three hot wires which are 240v from ~ to ~ but are actually 138v from ~ to N.
To understand this better, draw up a delta.... (an equalateral triangle, where each side represents 240v to scale). Say you make each side of the triangle 240mm (representing 240v). Now mark the exact centre point of the triangle which represents neutral. Scribe a line from the triangle corners to the centre. Now measure from any of the triangles points to the centre N. You will find that it is 138mm (representing 138v).
Now..... Add up the 3 phases..... 3x 138v and tell us what you get.
Of course there is a trig equation that represents this as well, but I prefer to explain with drawing and measuring rather than trig.

If you have an older star wound motor, you will have to do some brain surgery on it to get it to run 240v delta.... ie, remove the rotor from strator, locate the windings star point, cut and extend the wires to the terminal box. When connecting them up to power, you will have to ensure that the windings connections are sequenced so that motor will start.

I would do some more reading up before starting on the project.
Practical machinist, Home shop machinist, lathes.co.uk or many others have the info that needs to be ingested.

Also.... I am not an electrician, and am in no way an expert on this subject. I have just researched the subject material for a couple of years now, and want to share some of the info that I have learnt. I am open to corrections from anyone who would like to chime in here.

Have fun.

Fossil I have enjoyed reading your postings but feel the need to correct some of your numbers.

The 4 wires coming from the street to any premises are: Neutral, and three hot wires which are 415V from ~ to ~ but are actually 240V from ~ to N. Draw your scaled delta with 415V (or 415mm) length of sides and then draw your star inside that delta with lines going from the apex points to the centre and measure the length of the star lines you should be measuring the ~ to Neutral being 240V or 240mm.

When power engineers quote a 3 phase voltage the standard definition means the voltage measured across phases.


When single phase supply comes into you house it is a ~ and neutral conductor. This provides 240V.

The industry standard 3~ motor is wound delta with 415V ~to~. If you redraw the same delta to become a star then you need 690V ~ to ~.


You need to check your motors carefully the nameplate I saw said the motor was connected delta for use with 415V 3 phase power. I vaguely remember from my time in the steel mill having 240V 3 phase motors on equipment we brought in from Italy. If both ends of each winding had been brought out we would have changed them to be 415V star connected but instead had to use a drop down transformer to operate the equipment.

Your understanding of the delta to star transformation is excellent and an area many just don't grasp. If I can better explain please let me know. I only offer the advice to help you avoid applying too low a voltage to you motors and suffering them run underspeed and potentially buring out.

Cheers,
Blackout

Thanks very much for pointing that out Blackout.

The phase converter project turned out to be a 5hp unit as the 10hp idler that I have, is wound for 415v delta, as you point out. I have been learning as I go, and as I re-read some of my posts, I realise that I have been handing out advice, as a consequence of my enthusiasm at my new found knowledge. This has been a mistake, as I have not given correct info in some cases, as you point out. Thank you very much for clarifying the issues.

I am presently on the lookout for a suitably sized transformer, which will allow me to run larger motors, which all seem to be 415v delta, above 5hp. The smaller motors, (5hp or below) are readily available in 415 wye 240 delta, which is what I have used for the converter shown above. All of my present tool motors are also wired 240 delta, so all is fine there. The only motors that I have had a little problem with, have been two small (1hp) 3 wire star wound old motors. One was for my drill press, and the other is on a grinder. I stripped them down and cut the windings at the star point. I then extened the wires to the terminal box, so that I could wire them up in delta configeration. This worked out very well.

Anyway, back to my mistakes in info above...... Moderator, I am feeling a bit silly at leaving incorrect info in the public domain. I would like to modify or delete some wording on the previous posts in the interests of accuracy and safety. Can yuo let me know your thoughts on this?

Thanks again Blackout.

Fossil

Hi Fossil,
I am a newly registered member as of today but have been reading this thread for the last couple of months as a guest with great interest.

Your final unit looks terrific... a job well done.

I too have been making my own converter, inspired by your project, also with 240v ~to~. Happy to send you some pics if of interest.

My current configuration however needs a beef up though. I am wanting to run a 5.5hp (22cfm) air compressor which is not he easiest load to start with. Like you, I opted for the 240v setup to avoid the step-up transformer costs, which meant I needed to change the 415 delta motor which was standard on the compressor unit. This is where I fell down. Being the one to try and do everything for no cost, I scrounged two 4 hp dual voltage motors from work but they are not sufficiently sized and the compressor motor draws too much current at full pressure resulting strobing of my shed and house lighting.

Like you I have had difficulty finding larger dual voltage motors above 4-5hp at work. Luckily I have a contact at my scrap yard, so on Monday I am off to sift through 28T of electric motors to see if my luck changes.

I also want to alter my setup to have the phase converter switch off on on with the compressor cycles, but haven't designed the circuit yet. Currently the converter runs full time and has a timed idler start circuit. I also want to introduce a second timer and contactor so that the output voltage isn't available until the idler has started running.

Have you created a wiring diagram of your final unit? I notice you now have 5 run capacitors rather than the original 3. What capacitance did you end up running to achieve the 1.5%?

Where did you end up getting your capacitors from? Was it the US as earlier suggested?

Thanks very much for sharing your experiences as you went along. Not being an electrician, the discussions gave me additional areas to investigate as I went along. In fact it has become more an obsession than just a learning experience.. just ask my wife..

Well done again.

Fossil,

I enjoyed your post and engineering skills and understanding. I interested in how easy it is to access the star point of small motors and bring them out into the terminal box.

Just for your interests sake industry has been reconfiguring 3P 400V motors to run 690V (~ to ~) by converting delta configuration motors to start configuration. We do this to allow us to run longer distances with the same cable or reducing the size of cable for the same distance.

I think I heard that under a certain size they coudn't be reconfigured and would cost more to buy them at 690V so we run the smaller motors at 400V, now I think I undertsand this there is a crossover point around 5.5kW. It means another votlage of transformation in the system. Exisiting 400V equipment has been tested for the 690V operation and with test certificates are used for 690V (I don't know if manufacturers have had to make changes to achieve the air gap clearances for insulation or improve insulation materials).

We use standard 3 phase power cable which is typically rated 0.6/1kV meaning insulated 600V above earth and 1000V between phases.

Does anyone use a method of ganging up single phase motors through a single shaft to drive the bigger motor? On mining conveyors we do transfer power into the conveyor belt by connecting multiple motors through gearboxes to the conveyor belt pulleys. I have even done it on 11kW motors.

Cheers,

Blackout

dear fossil.
i hope you can help. iam new to this forum i have recently bought a phoenix 5-8hp static converter from the u.s. i bought it to run my car hoist (screw type) 5hp. the diagram they sent was crap. http://www.appliedindustrialmotors.c...cSC%5B1%5D.gif iv tried endlessly to contact the but with no luck . i was reading that the u.s have 2 hots both at 120v is this the case? iv ask a few lecos and no one wants to help.. i have included pics of the converter and the hoist . i hope you can help as iam just about to turf it. thanks alot
djay.

Hi djay, welcome to the forum. In case Fossil doesn't see this, can you please provide a full size picture of your motor's data plate. All of the information on it must be visible to provide a useful answer.

Static converters are widely regarded as crap on the U.S. forums that i read. And yes, North American mains is 120 volts. They run two actives at 120 each to provide 240, unlike our 240 active + neutral. In many applications it doesn't matter, such as some VFD (VSD) units. If your motor is 415 V you will require a step-up transformer in any event.

Greg