240V/1ph--440V/3ph

[catgate]

Now, after seeing this I can almost believe that Toady B liar can walk on water.
I had a call for help from a friends son. He is running his lathe (1.5h.p. motor) from a proprietary phase converter (Transwave). When I looked inside it I was gobsmacked. It does not have a transformer in it and yet, running off 240v mains, this box with a motor grafted on its back, turns out 440v 3ph.
Basically 240v is fed in, there are 3 capacitors (two that I think could be 60mfd and another about 30mfd), then the 240v plus the capacitor out puts, three wires, are fed out to a motor, affixed to the back of the box, and back from the motor are returned three wires carrying 440v 3ph.
How is it possible to get out 440v when the input is 240v with no transformer? Is there some funny business using the capacitor outputs in series? But how can you couple capacitors in series? Am I dreaming? Is there really a Father Christmas? When will those nice men in the white coats come again? Does anyone know the answer???

[chameleonrob]

You're not dreaming, you can have box with 1 ph 240v going in and 415v 3hp coming out as each of the three wires coming out of the box on the three phase side will each be 240v but at a differant part of the AC cycle Sine wave. The way it is worked out is as the peak voltage will be 240v you multiply this by the square root of three to give you 415v or normal three phase supply, by adding the voltage in each wire you can get the 440v, .

As an aside, power is generated in 3 phases by having three coils on the generator each producing one of phases and each is 120 degrees away from the other two, it can then be trasmitted along 3 wires (3 lots of 240 in phase with each other would need 6 wires). it can be split at the sub station so that street A get the fist phase, street be gets the second and street 3 gets the third. factories can get all three in the three phase form so they can get more power without the need for a different voltage

[Tel]

Now I'd really like to be able to do that - anyone got a circuit?

[catgate]

Thanks for the reply, chameleonrob, but I have not entirely understood the principle. I am aware of the normal method of generation and supply of 440/240 mains current, but this still has me foxed. Where and how do the capacitors come in, in your scheme, and how is the 240, and the capactors' output, connected to the motor which is grafted on to the box and from whence comes the 440?
Like Tel says, it would be nice to see a circuit diagram of this miracle.

[jackrae]

Without wishing to write an exhaustive e-mail to the board on how to actually build one, may I suggest the following website for details of how such a system might be put together.

www.metalwebnews.com/howto/ph-conv/ph-conv.html

It might also be that one of the capacitors mentioned is directly across the 240 mains incoming line to act as power factor correction, since the system will be a highly inductive load. PF correction helps eliminate wasted "reactive" energy by getting the line current into phase with line voltage.

regards

jack

[catgate]

Thanks Jack, but your link article refers only to turning 240v 1ph to 240V 3 ph. The only way to run a 440v motor on this system is to turn it from delta to star so that each motor winding is across 240V. The magic that I have seen converts from 240 to 440 without a transformer (apparently).

[chris vine]

I think the bit that may be missing is how the motor is connected and also the voltage of the motor windings.

It seems that the motor grafted on the back is a slave and it is probably a 240/415 volt motor. If it is wired for star configuration and the 240 volts is applied across one winding and the central star point then the voltage across any two of the three motor terminals should be 415. In other words the motor is working a bit like an auto transformer but with a phase shift so that the total voltage works out at 415 and not 480.

I am probably completely wrong but it is free!!!

Cheers
Chris.

[jackrae]

It's reported that there are only 3 wires going to the motor unit so I suspect it is delta connected.

I surmise the motor unit actually has 6 windings arranged as 3 pairs.

Let's call the A-phase pair A1--A2 and A3--A4
B and C phases are similarly numbered

If the windings ends A1,C2 and C3 are connected together and same for B1,A2,A3 and also C1,B2,B3 we have a delta grouping with the free ends A4, B4 and C4 acting as star tails.

With 240 volts on the delta winding we will get 480 volts on the star ends (assuming all windings are of equal turns ratio). With volts loss in windings due to external motor load this could end up at the quoted 440 volts.

With the 240 volts mains connected to two of the delta points, say A1/C2/C3 and B1/A2/A3, and a capacitor between this latter point and C1/B2/B3 we will get sufficient phase shift to rotate the motor at near synchronous speed. This will result in a 440volt 3-phase appearing at the ends of the star points A4, B4 and C4.

I surmise there will be a switching relay or timer to switch/transfer capacitors once the unit is up to speed to maintain sufficient phase shift when the unit is under laod. The remaining capacitor is probably PF correction as previously suggested.

I trust you followed all that, if not I could post a sketch if someone can advise how

regards

jack

[catgate]

Thank for that Jack. I have pondered on the thing all day, on and off, and I was just going out into the workshop to try my own "solution". Which was to wire up the motor both star and delta, and feed in 240v using capacitors, to cause phase shift, in the "star" config., and then measure the "delta" voltage. I was going to wear a hard hat and rubber gloves, and say three hail mary's first. Then I suddenly thought, " I will look on the forum before I go to see if anything has turned up."
Now I will reread your message and digest that before going and throwing the national grid into chaos.

[catgate]

Fortunately I pondered on your messages before going out and trying my "solution". It saved a waste of time, because, as a result, I realised my idea was seriously flawed! A Jackrae diagram would be very useful. I imagine that the motor therein described must be a fairly unusual animal, and would have to match the motor on the machine for h.p.. Do these occur in the wild anywhere. The only things that spring to mind are possibly some of the modern washing machine motors, but they would be too small for "serious" use.

[jackrae]

Hi Catgate

The type of motor I referred to has 2 sets of windings for each phase.
Basically this permits the motor to be suitable for either 240 or 415 volts wired as either star or delta. Normally each pair of phase windings would be parallel connected when used at 240 volts and series connected when used at 415 volts.
As you say, not the usual run of the mill motor (but certainly not a "special").
However I'll have a look through some catalogues at work tomorrow and see who supplies what.
regards
Jack

[catgate]

Thanks Jack, that would be useful. What set out as an almost acedemic enquiry to help a friend's son has now turned into something of a personal quest. I have just bought a Colchester Triumph and this turns out to have a 5hp 440 3ph/240 1ph motor on it. I feel it might be "over motored" but if I can find a way of easily producing 440 3ph without a roaring great transformer so much the better. Although it still looks like a much stronger MCB will be needed, and some stronger "string".
regards
G

[jackrae]

www.joliet-equipment.com/terminal_markings_and_connections-3ph_motors-single_speed.htm

Go to the above for a whole host of wiring configurations of 3-phase motors

I had a look through our catalogues but dual voltage manufacture in the UK appears to be like hunting for hen's teeth. They all come back with 230 on delta and 415 on star. Not exactly what we need

In the USA they used to (might still do) distribute 3-phase at either/both 220 and 440 volts. hence dual voltage (6 winding motors are quite usual there)

I'm sure in days past I've seem motors here in the UK with more than 6 terminals but that could have been a very long time ago.

An alternative might be to get a 1-phase motor directly coupled to a 3-phase motor configured in star and when its up to speed stick the 230 between the star point and one of the star legs. (with some capacitors to the other legs) If it works this should then give you 415 across the star points. At that point you may then be able to switch off the supply to the single phase motor.
I once tried something similar driving a 3phase motor with an electric drill and even without forcing mains onto one of the legs the motor actually self excited at full system voltage. Yes both me and my collegue were somewhat surprised.

I've recently read that doing it this way is about 70% efficient so if you want 2 horse out you'll need something like a 3-horse motor to act as the generator.

Remember however that ALL of the electrical power comes from your domestic supply line so be well fused. An ammeter (clamp on type) is extremely useful when trying such things.

[catgate]

Thank you for your efforts, Jack. It looks as though it is not going to be as readily achievable as I was beginning to hope. Earlier today I was talking, on the phone, to a friend who lives many, many miles from here, in Wales, and who is a paragon of encyclopeadaic electronic knowledge, and he came up with the same explanation as yours. However he too was at a loss to identify a suitable, commonly available candidate.
So, it looks as though "convention" will have it's way again...blast.

[Deleted]

There has been a lot of very knowledgable technical discussion on this subject all of which is over my head as I get nervous joining 2 wires together.

I have a 3 phase power supply which I pay a standing charge for but never use since the machinery it worked was changed a few years ago (graindryer).

I could extend the 3 phase supply into my workshop at a modest cost as I only have the standard 240 volt supply in there at present.

Is it likely to be worthwhile ? ie I need to buy a bigger milling machine and would 3 phase be much better?
Like I said I am a complete electrical novice.

Regards

Jim

[jackrae]

Without doubt, if you have 3-phase available to you this is by far the best motive power for any size of machine - bar very small "domestic" type motors.

The torsional vibration (pulsation) from 3-phase motors is virtually nil compared to single phase. You will have no troubles with starting and the power limitations of the standard 13A socket will be eliminated.

As a legacy of a previous owner, I have 3-phase available to my house (he decided he needed an infinite number of storage heaters so the local board run a supply cable to suit) The price of electricity soon put paid to them. Although I have to admit, the only machine I have rigged to operate is my milling machine.

Note that you WILL need to get a proper installation done by a competent electrician. And you must be aware that 415 volts exists beteen phases. Under new granny state rules you are prohibited from doing such types of electrical installations if not suitably qualified.

Note that I use the term competent rather than certified or qualified. My opinions of such pieces of paper in the hands of incompetent but certified individuals are better left unsaid.

There are bold electricains and there are old electricians, but there are few old and bold electricians

happy milling
jack

[Deleted]

Thanks Jack. I do have a very good local electrician who has done work for me in the past. I would never attempt any serious wiring myself - its just not worth it.

Regards

JIm

[ChrisCrosskey]

jackrae said:

Without doubt, if you have 3-phase available to you this is by far the best motive power for any size of machine - bar very small "domestic" type motors.

The torsional vibration (pulsation) from 3-phase motors is virtually nil compared to single phase. You will have no troubles with starting and the power limitations of the standard 13A socket will be eliminated.

Got to add my one fiftieth of a dollar here....
I replaced the original (single phase anti-vibe mount) motor on my 1948 Myford about a year ago with a three phase motor running from a small modern inverter.... both items were picked up for peanuts on ebay, total cost was less than I would have paid for a new cheapo motor...... they've transformed the machine, it's way quieter, and far far smoother than it was before..... three-phase really is the way to go, and if you've got it coming in for almost free (or very cheap) then really it is a good idea to use it.... also if you can find a three-phase to three-phase inverter (ebay would be a good place to start) then you can have speed control thrown in too..... I don't have to do much belt changing any more and I can't remember the last time I bothered with backgear......

chrisc

[David Thompson]

Are you quite sure you get 415V output?

I have an Invertek drive attached to my Boxford, but I had to re-wire the motor inside the switch box to change it from star to delta ( or do I mean the other way ?). So it used to work originally on 415V phase to phase, but now it works on 220V phase to phase or thereabouts. It is still a 3 phase motor with all the advantages of torque and smoothness, but it is at the 3 phase supply level which corresponds to 120V phase to neutral rather than the 240V phase to neutral we are used to in domestic supplies. The motor is a "dual voltage" type so that it can be easily adapted to 415 or 220 V 3 -phase supplies. The lower 3-phase voltage might be needed because the motor could be used in America, or in an industrial system in the UK.

The motor now draws more current than it used to, but at a lower voltage, so the power and torque are not affected. It just runs now as it might have done if exported to the USA, except for the matter of 50 to 60 Hz frequency change which would have altered the speeds. I think a different speed plate would have been fitted for export.

My Invertek drive has a lot of solid state electronics as well as capacitors, so the 3 phases are regenerated at a variable frequency which allows motor speed control, but it does not need a transformer because there is no actual increase in voltage. I have never actually shifted the belt across the pulleys since I installed this system, although I do use back gear for hard work.

[chris vine]

On the same note, I fitted my super 7 with a three phase motor and single to three phase inverter with speed control and it is excellent. No vibration and I hardly ever shift the belts from the top speed. Mine was supplied by Newton Tesla who advertise in ME, more expensive than ebay but very good.

Only downside is a high pitch whine, from the motor, but as I get older the ears will filter it out!!
Chris.