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I need some help undersatanding 3 phase motors

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april

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I am looking for a brief primer on these. I don't want to have to spend a week reading in depth but rather just a brief summary .
Anyone have a favorite site ?

My problem is a 3 phase brick saw with a 4 HP motor but thats about all I can read from the placard on the motor . It mentions two voltages too a high one and a low one I suppose . Don't understand that . I thought all 3 phase was all 450 Volts?

So I go into the connection box and again it says high and low voltage,see pic attached

I'm connecting another single phase motor instead for a try and I would like to use the existing wiring and switchbox and leave one wire disconnected .
 

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April,

Applying single phase to 3 phase motor will not work. If you look at how a 3 phase motor works it does it by a rotating magnetic field. That being said.

This is a high voltage device. If you do not understand do not experiment. This can cause personal injury. At this level of energy, arc flash is an issue. Do not mess with it.

Contact a qualified electrician for assistance.
 
April,

Applying single phase to 3 phase motor will not work. If you look at how a 3 phase motor works it does it by a rotating magnetic field. That being said.

This is a high voltage device. If you do not understand do not experiment. This can cause personal injury. At this level of energy, arc flash is an issue. Do not mess with it.

Contact a qualified electrician for assistance.

Totally agree. I would highly advise getting someone to assist you.

That said, star wound 3 phase motors can be run on single phase. https://dcacmotors.blogspot.co.uk/2009/04/running-3-phase-motors-with-1-phase.html

Not sure about delta wound motors...
 
OK, lets try some simple bullet points:
A three phase motor has three stator windings.
There are two ways to connect those three windings, "star" and "delta".
In the Star (sometimes referred to as a Y (wye)) configuration, one end of each winding is connected to a common point (the Star Point).
In the Delta configuration, the windings are connected end to end in a closed loop.
For both star and delta connections, the phasing of the connections is important.

If the individual windings are rated for 240volts, then a delta connection will run from a 240v three phase supply.
Reconnecting into a delta configuration will enable the motor to run from a 415volt three phase supply. (240 x √3 = 415).

So, Delta is the "low voltage" connection and Star is the "high voltage" connection.

When a three phase motor is is connected to a three phase supply, it will start to turn.
If the motor turns in the wrong direction, swap over any two of the three connections and the motor will turn in the other direction.

When a three phase motor is connected to a single phase supply, it will just sit there humming to itself.
If the rotor is turned (by hand? Mind your fingers!) the rotor may spin up to normal speed, but the power available from the motor will be limited.
This fudge is sometimes used to make a single phase to three phase converter.

Does this help?

JimB
 
deleted due to errors in my under standing and experience
 
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see previous post
 
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"I thought all 3 phase was all 450 Volts?"



It depends where you live......
Some areas, like Japan, it is 100 volt phase to neutral, North America is 120 volt phase to neutral, while most of the world is240 volt phase to neutral, although there are some areas in South America and the Middle East where it is still 220 volt phase to neutral.

In all cases, to obtain the phase to phase voltage, multiply those voltages by √3
 
"I thought all 3 phase was all 450 Volts?"



It depends where you live......
Some areas, like Japan, it is 100 volt phase to neutral, North America is 120 volt phase to neutral, while most of the world is240 volt phase to neutral, although there are some areas in South America and the Middle East where it is still 220 volt phase to neutral.

In all cases, to obtain the phase to phase voltage, multiply those voltages by √3


common 3 phase voltages are (USA) are 120/208, this is used where most of the power is residential and some businesses need 3 phase, so it's 120 phase to ground and 208 phase to phase,
240 volt, 480/277, this is industrial and large offices with lots of 277 volt lighting and 480 volt for motors and equipment, (very vicious when you get shocked)
 
There is a safety video on youtube, which shows a dummy subjected to a 480V industrial switchgear explosion.

The "burns" that the dummy suffers are simply amazing. After watching the video, one develops additional respect towards electricity.
 
JimB said:
If the individual windings are rated for 240volts, then a delta connection will run from a 240v three phase supply.
Reconnecting into a delta configuration will enable the motor to run from a 415volt three phase supply. (240 x √3 = 415).

So, Delta is the "low voltage" connection and Star is the "high voltage" connection.

Kinarfi said:
NOT correct!!!! low voltage, delta or wye, refers to motor with two sets of winding, low voltage refers to hooking the winding up in parallel and high voltage refers to hooking them in series. This allow the motor to have the same power at 220 volts as at 440 volts. What you said allows a 440 volt motor to be run on 600 v, but you have to have a 12 lead motor and know what your doing.

I stand by what I said above.
There may be motor with two groups of windings which may be connected in parallel or series in order to give a low/high voltage rating.
However, the motor terminal box pictured in the first post has only three windings, and the description (in several languages) shows the star connection as "high voltage, and the delta connection as "low voltage".

In three phase circuits, the relationship between star and delta voltages and currents is √3.
Multiply or divide by √3 as appropriate to convert from one to another.



JimB wrote:
When a three phase motor is connected to a single phase supply, it will just sit there humming to itself.
If the rotor is turned (by hand? Mind your fingers!) the rotor may spin up to normal speed, but the power available from the motor will be limited.
This fudge is sometimes used to make a single phase to three phase converter.

Kinarfi wrote:
And your fudge is an excellent to burn a motor up, the industry goes to great lengths to prevent single phasing 3 phase motor with "detectors" and thermal overloads.

Kinarfi also wrote:
Very interesting reference, also known as RotoPhase converter some 30 years ago, always wondered how the worked,

JimB says: Make your mind up old chap, The RotoPhase and the system advocated by tcmtech are basically what I said with the addition of a couple of capacitors.

JimB
 
April,Applying single phase to 3 phase motor will not work. If you look at how a 3 phase motor works it does it by a rotating magnetic field. That being said.

This is a high voltage device. If you do not understand do not experiment. This can cause personal injury. At this level of energy, arc flash is an issue. Do not mess with it.Contact a qualified electrician for assistance.
God protect us from the do-gooder Wowsers
A bit of contradiction to your name I think

You have misunderstood anyway
I have some knowledge of driver devices from single to 3 phase but at a cost of $900 for the device to do it I am changing the motor , physically
I have a second single phase motor I am going to run on it and rather than leave the old wiring hang I hoped to maybe use two of its wires and an earth .
Hope that is clearer and you know what you can do with your warnings.

Thanks to the other posters .

JimB , thanks again


More I want to get some knowledge of 3 phase and I will refer to the site mentioned , thanks.
Thats what I was after there and probably should have split the post .
 
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If you want to run it on single phase and get its full power rating see here.;)
https://www.electro-tech-online.com/threads/3-phase-converter-schematic-miller-system.100563/
Still amazes me how many people here don't even know what useful information in the other sections of this forum! :eek:

Thanks
I found that thread interesting and to the point. I am tempted to mess around with the original 3 phase motor just to see if your design works.

Finding this sort of stuff on the site is another matter
Your search pattern has to be well considered and formulated . If you have little knowledge of the subject, that can be impossible to do.

I tried a bit of searching on this and got hundreds of hits which did not relate to what I sought
This is a common occurrence here . The search pattern seems to be more demanding .
 
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OK, lets try some simple bullet points:
A three phase motor has three stator windings.
There are two ways to connect those three windings, "star" and "delta".
In the Star (sometimes referred to as a Y (wye)) configuration, one end of each winding is connected to a common point (the Star Point).
In the Delta configuration, the windings are connected end to end in a closed loop.
For both star and delta connections, the phasing of the connections is important.

If the individual windings are rated for 240volts, then a delta connection will run from a 240v three phase supply.
Reconnecting into a delta configuration will enable the motor to run from a 415volt three phase supply. (240 x √3 = 415).

So, Delta is the "low voltage" connection and Star is the "high voltage" connection.

When a three phase motor is is connected to a three phase supply, it will start to turn.
If the motor turns in the wrong direction, swap over any two of the three connections and the motor will turn in the other direction.

When a three phase motor is connected to a single phase supply, it will just sit there humming to itself.
If the rotor is turned (by hand? Mind your fingers!) the rotor may spin up to normal speed, but the power available from the motor will be limited.
This fudge is sometimes used to make a single phase to three phase converter.

Does this help?

JimB

Sure does Jim
Reconnecting into a delta configuration will enable the motor to run from a 415volt three phase supply. (240 x √3 = 415).

So, Delta is the "low voltage" connection and Star is the "high voltage" connection.
Sort of answers it all
In my Picture then it is set for low voltage so requires a 240V 3 phase supply. and connecting it as shown for high voltage will enable it to run on a 415V 3phase supply.

I did think that thats all we had in Australia for 3 phase ..415V but as this has been running somewhere here as configured that must not be the case.
 
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star wound 3 phase motors can be run on single phase. https://dcacmotors.blogspot.co.uk/2009/04/running-3-phase-motors-with-1-phase.html

Not sure about delta wound motors...
More difficult to understand
Is this saying you run a 1HP motor with no load and then tap off the 3 phase power to the motor you want to run?
If so can you get enough out to power a 4 HP 3phase motor or must you be running say a 6HP single phase first and tap it?

Seems like a horrible waste of energy running two motors
 
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Well it amazes me that you would post on my thread with so much red!
I suppose the chance to show your expertise got the better of you .

Seriously though, thanks anyway.
I found that thread interesting and to the point. I am tempted to mess around with the original 3 phase motor just to see if your design works.

I could care less about how much red someone has by their name let alone how they got it! :p

If I see a question relevant to my knowledge base I try and help.:D

Personally I find the whole rating system here rather pointless but then I never was a team player any way. :p

As far as my design goes I have built and sold too many to count and I have several in my shop that have put in daily service for nearly a decade now with little to no maintenance.

Also given my threads view count and the thank you PM's I have had over the last few years the odds are there are several hundred more out in the world doing just fine.

If you build one and get the numbers for the parts even remotely close the odds are your 4 HP motor will do just fine.;)
 
I need to pointout to everyone that there is a 3 phase system called High Leg Delta: https://en.wikipedia.org/wiki/High-leg_delta
Does that affect my situation at all KISS?

I have been giving tcmtech a grilling on his posted schematic to try to get the probable values to run my 3 Phase direct. I'll come back here to leave his thread with less clutter.

I burned out my 2 1/2 hp single phase after cutting about 100 bricks . The 5 amp current cutout went first , then the start capacitor started to smoke , then the motor started to smoke and the power dropped away finally. ( all on separate days) .It still runs with no load but won't run the saw . It was throw away anyway .Rusted and past it. I cannot tell if this has a starter contact inside as to dismantle it would have been to destroy it anyway but I can get it off and have a look now . I suspected there might be and it might have been sticking on from time to time.

When running properly it seemed to cut well.

The 3 phase motor is not throwaway however and I am trying to make sure I don't burn it out. Using tcmtech's Miller system you don't get a lot of time to take measurements of voltage and I hate working on 240 V anyway. Just risky.

If you are there tcmtech , do you have any suggestions as to how to box up your device with safety in mind . You did not answer my question on the a/c potential relay.. I was looking to find one on Ebay and get a couple.

I'm going to build and try this so any help from someone who has done it would be appreciated or any good pics of the containment box and physical layout would be helpful

Do-gooders who want to post warnings need not apply !

Thanks
 
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That was a grilling? :confused:

For your motor I would start with a pair of 30 - 40 uf run capacitors and any starting capacitor between 250 and 400 uf. Relating to a starting relay I would suggest this one. **broken link removed**
It's in the same number range of the ones I use plus they are rather easy to take apart and fine tune if needed.

I am not sure how you figure you only get a short time to measure things being that if the motor is up to speed it should be able to run that way for whatever time rating it has. :confused:

Relating to the voltage sensing relay for automatic starting as with my posts in the converter thread say most any voltage sensing relay will work being that internally they usually have some type of adjustments to raise or lower their pullin voltage point.

If you don't have a VSR you can just use a heavy duty normally open push button switch and use that as a manual starter. Turn the power on while holding the start button down then release the start button once the motor is up to speed.

As far as protecting your motor from future burnout from overloading I would suggest not using any power circuit over 20 amps. If you are still unsure then drop back to a 15 amp circuit until you have gained confidence in your setup.

My old backup air compressor is a 5 HP commercial unit with a stock 3 ph motor and that has been in service for over 10 years and has yet to ever cook a motor simply due to it having a 20 amp circuit. The breaker trips log before the motor ever has a chance to get too hot if it ever has problems getting up to speed in time.
 
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