3 Phase to Single phase

Discussion in 'General Electronics Chat' started by alxdg, Nov 29, 2010.

  1. alxdg

    Thread Starter New Member

    Oct 26, 2009
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    I would like to know how you could go from a 3 phase output to a single output, I have seen a way where all three leads are connected together and they all go to L1, is this a good way of doing it?

    Thanks for all of you that want to help me
     
  2. GetDeviceInfo

    Senior Member

    Jun 7, 2009
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    That would be a very bad way.

    Between any phase would be considered single phase.
     
  3. PRS

    Well-Known Member

    Aug 24, 2008
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    If your 3 phase is Y connected with a neutral leg then you get single phase between any leg and that neutral leg. It's a bit different for Delta connected systems. Do you know what you are using?
     
  4. PackratKing

    Well-Known Member

    Jul 13, 2008
    850
    215
    Sure is....... that is if you like lots of sparks, fire and electrocution. :D

    Three-phase, is exactly what it implies, three distinct / separate hot leads of the same voltage to a neutral, "Y" or tied for line feed to the corners of a delta / Δ / arrangement with no neutral / return.

    See: http://www.allaboutcircuits.com/vol_2/chpt_10/5.html
     
  5. retched

    AAC Fanatic!

    Dec 5, 2009
    5,201
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    3-phase is 3 phases.

    IF you need single phase, just use 1 wire.

    Meter to ground to see if you get 120v as you have to check because you may have a 600v supply.

    If 1 phase voltage is greater than what you want, use a properly rated transformer to bring down the voltage.

    If the voltage is proper, use an isolation transformer. Also known as a 1:1 transformer.

    Be careful as you can. Mind your pinkie fingers, especially in a crowded box.

    Actually, call an electrician.
     
  6. PRS

    Well-Known Member

    Aug 24, 2008
    989
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    Yes, to what retched just said. Use a voltmeter. But it seems you don't really know what is going on. I suggest you call an electrician, too.
     
  7. alxdg

    Thread Starter New Member

    Oct 26, 2009
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    Hello Everybody and thanks for all the replies.

    I think I should have added a little more information, the 3 phase output comes from an inverter then through a in line choke per line then all the 3 lines are tied together in a common node L1. This really looked odd to me and thats why I started this post. Any idea on whats going on here, who is this being done

    Thanks in advance
     
  8. retched

    AAC Fanatic!

    Dec 5, 2009
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    It was done by someone who wants to kill you.

    That, or someone who wants a new inverter.

    There is no reason to tie 3 phases together on 1 lug.

    Is anything working?

    Are you sure its 3 phase and not 3 outputs on the same phase?
     
  9. alxdg

    Thread Starter New Member

    Oct 26, 2009
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    Hello everybody

    The outputs come from a power module (Mitsubishi PM25RSK120) the system was design to run as a 3 phase then It was modified to run single phase, and that what I am trying to figure out. Everything works its an inverter that can put out up to 6KW.

    Thanks for all of you
     
  10. GetDeviceInfo

    Senior Member

    Jun 7, 2009
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  11. BillB3857

    Senior Member

    Feb 28, 2009
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    If the inverter was MODIFIED from a 3 PHASE output to a SINGLE PHASE output, it is possible that internally, the 2 of the original 3 phase driver signals were disconnected and all 3 output sections are being driven by a common drive signal. Effectively, that would parallel them. One danger with that method is that the module with the lowest internal resistance will tend to hog the load. Some means of load equalization needs to be present.
     
  12. GetDeviceInfo

    Senior Member

    Jun 7, 2009
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    It would appear that any number of igbt pairs could be driven for a single or multi phase output, but if, as indicated from the OP, that all 3 pairs are producing a paralleled output, where can the common return be found? Unless of course a second driver group is suppling that. It could even be that 3 driver groups are ganged to supply 3phase power.
     
  13. BillB3857

    Senior Member

    Feb 28, 2009
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    If a bi-polar supply bus is used, the zero point (center tap) of the supply would suffice as a return line. Sometimes brought out to an external terminal
     
  14. GetDeviceInfo

    Senior Member

    Jun 7, 2009
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    I suppose the OP could enlighten us as to this configuration.
     
  15. alxdg

    Thread Starter New Member

    Oct 26, 2009
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    Hello,
    I am not sure about what you are asking, you mentioned something that got me thinking, so if all the lines are in phase coming out of the IPM, can all the lines be tied to the same terminal?, what is the most common frequency to control the IPM for a 60Hz application?

    I have another question, What is the difference between a line reactor and an inline choke?

    Thanks for your help :)
     
  16. GetDeviceInfo

    Senior Member

    Jun 7, 2009
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    I think it's pointless to ask any further questions if the basics aren't realized for your original query.

    Schematics may be required for the utlimate answer, but it's going to be a test of your skills as well.

    In a single phase supply you have two lines, an example would be hot and neutral. In your case, you appear to have a hot made up of 3 parallel drivers. my question is, how is the neutral obtained. Is it a center tap off the DClink or another phase driver.

    We know nothing of the load characteristics at this time, but my first (next) question would be, if centre tapped off the link, is it grounded.

    It's possible that the OP miss termed the original query by using the term 3phase. What you have is a module that has 3 stacked drivers that are externally driven. In my experience, equipment designed around a 3phase driver is done so to service the load, and as such, would not have access to the DC link as a seperate source.
     
  17. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,749
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    I suggest that OP show us the device connections, before he blows it up and lit the place on fire
     
  18. BillB3857

    Senior Member

    Feb 28, 2009
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    A look at the data sheet for the driver shows that each module is configured to drive 3 phases, labled U, V, and W. These labels are typical of brushless DC motor terminals. Again, looking at the data sheet, it appears that the drivers are indeed connected to a positive and a negative bus for a 3 phase H bridge configuration. The 7th driver is for application of voltage for brake control. A configuration like this would require a center tapped supply with the center tap being used as the return in order to supply single phase. For three phase output, the center tap could be either not connected or grounded. Either Y or Delta three phase . What is unusual is that the OP's unit has three of these driver modules. with apparently all 9 outputs (3 x U, 3 X V and 3 X W) all connected together. Unless I'm reading the OP wrong.
     
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