Connect with us

Convert 1ph to 3phase for motor

Discussion in 'Sensors and Actuators' started by BlinkingLeds, May 4, 2013.

  1. BlinkingLeds

    BlinkingLeds

    180
    0
    Feb 23, 2013
    Hello to everyone , I have a 3phase pump for water which is 150 feet underground and i want to be able to power it from my little 1phase generator in an event of a fire and a blackout (this has happened before). I've got a PS21243-AB DATASHEET and i wonder if i can do that with this. I don't know if i can supply 3phase square wave AC to a motor that normally has 3phase sine wave AC. Is there a problem with that?.
    although i think i can make it work (but not so sure about it :) ), any suggestions on how to wire up this chip correctly will be greatly appriciated.
    Thanks in advance.
     
    Last edited: May 4, 2013
  2. DuctDuck

    DuctDuck

    52
    0
    Jan 26, 2013
    Sorry to dissappoint you, your IC selection is wrong for the application. From the datasheet link, fig. 2, the AC input has to be 3 phase (but its rectified). That is not a neutral-grn-live input connection.

    http://en.wikipedia.org/wiki/Scott-T_transformer
     
  3. BlinkingLeds

    BlinkingLeds

    180
    0
    Feb 23, 2013
    Doesn't this mean that it needs DC?
     
  4. DuctDuck

    DuctDuck

    52
    0
    Jan 26, 2013
    Your problem is very old! Desire for a powerful and versatile AC source to drive mechanical systems. Whew, better let off some steam during a bike ride.

    Waste some bandwidth and read about 3phase transformers and 3 phase loading, etc.

    There is no magical IC to interleave power for your motor.
     
  5. BlinkingLeds

    BlinkingLeds

    180
    0
    Feb 23, 2013
    This IC has 3 IGBT half bridges It means that if i supply DC to it it will make 3phase square wave AC doesn't it?

    IT states at the beginning "INTEGRATED POWER FUNCTIONS
    600V/30A low-loss CSTBTTM inverter bridge for three
    phase DC-to-AC power conversion
    "

    Isn't that exactly what i need?
     
    Last edited: May 4, 2013
  6. DuctDuck

    DuctDuck

    52
    0
    Jan 26, 2013
    Yup, 3 phase DC is what you need! Please refer to page 5/10 of your pdf link.

    Demanding those power levels from DC rectified single phase doesn't seem realistic.
     
  7. BlinkingLeds

    BlinkingLeds

    180
    0
    Feb 23, 2013
    what power levels? i only need 2kw max so i get one phase and get it through a rectifier bridge so now i have dc and i give it to the IC. The IC can now supply 3phase square ac
     
    Last edited: May 4, 2013
  8. BlinkingLeds

    BlinkingLeds

    180
    0
    Feb 23, 2013
    This is a DATASHEET of another IC i have
     
  9. DuctDuck

    DuctDuck

    52
    0
    Jan 26, 2013
    okay, fine...you have square wave 3 phase and you can point and laugh; not the rest of the population.

    A sqaure wave voltage pulse equates to a current pulse as well, implying larger than normal current draw and heat. Is this good for the motor's windings? It should be easy enough to calculate the differences in sine wave from square wave current waveforms. Motor failure is an eventuallity but predicted when?
     
    Last edited: May 4, 2013
  10. BlinkingLeds

    BlinkingLeds

    180
    0
    Feb 23, 2013
    Now that's exactly what i asked in my first post "Is square wave ac instead of sine wave good for the motor?" I really don't have an idea and i don't have a small 3phase motor to try it.
    Actually the second IC is from my air conditioner. I've seen the circuit it takes on phase runs it trough a rectifier bridge and gives DC to the IC. The IC produces 3phase AC (not 50hz but whatever frequency the uC gives to it , and that's how the compressor run at different speeds)
     
  11. BlinkingLeds

    BlinkingLeds

    180
    0
    Feb 23, 2013
    If the difference in the current draw is not very big i think the motor can withstand that because it's under 150 feet of 70 Fahrenheit water.
    If the current difference is big i can always reduce the voltage so it will not draw as many amps right?
     
  12. DuctDuck

    DuctDuck

    52
    0
    Jan 26, 2013
    hmm, fascinating.
     
  13. duke37

    duke37

    5,211
    718
    Jan 9, 2011
    You should not reduce the voltage on an AC motor, if you do, and the torque generated is not sufficient then there will be more slip and more current taken. Motor goes pop?
     
  14. BlinkingLeds

    BlinkingLeds

    180
    0
    Feb 23, 2013
    is there any other way to reduce it's current?
    and what do you mean "Motor goes pop"?
    Thanks.
     
  15. BlinkingLeds

    BlinkingLeds

    180
    0
    Feb 23, 2013
    This ic is going to work right?
     
  16. duke37

    duke37

    5,211
    718
    Jan 9, 2011
    I bought a book, "Alternating current machines" by Say for a few pence and found it interesting reading. This is the extent of my knowledge.

    As I understand it, the current is determined by the required torque and variable speed drives vary frequency and voltage. I would stick with the proper voltage and frequency.

    By pop I meant the sound made when the wires fuse.

    There are others on the forum who have more knowledge than me in electrical engineering, perhaps they will chime in.
     
  17. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,174
    2,689
    Jan 21, 2010
    Often changes in frequency need to be accompanied by changes in voltage to maintain the same torque (for induction motors??).

    But like duke37, this is not an area of expertise. I am just parroting what I have heard/read.
     
  18. BlinkingLeds

    BlinkingLeds

    180
    0
    Feb 23, 2013
    But if it's pumping water do i need that much torque?
     
  19. duke37

    duke37

    5,211
    718
    Jan 9, 2011
    Have you tried pumping water by hand? You need a lot of power.

    The torque may be low if the head is low but impeller type pumps seem to be designed to give a reasonable efficiency with high pressure, low flow and low pressure high flow output so the torque will not vary much.

    If you wish to alter the frequency, you can get drives which are fitted to lathes, also my brother has a vacuum pump for milking which has a variable drive so that it only pumps what is necessary so saves power. This will be a vane constant displacement pump.

    An impeller works by flinging the water to the outside, if the speed is too low, the pressure will be too low and there will be no flow.
     
  20. BlinkingLeds

    BlinkingLeds

    180
    0
    Feb 23, 2013
    Can't i alter the frequency with the IC i already have?

    Those variable frequency drives are costly :)

    The present setup has a pressostat so that the pump works for 1minute then it stops for 2minutes utill the pressure drops and it turns on again
    i read someweare that turning on and off repeatedly is not the best thing that could happen to a motor so i was counting on that ic to provide variable frequency as the output frequency of that IC depeands on the iput frequency which i can easily regulate
     
    Last edited: May 7, 2013
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-