Connect with us

Split phase induction motor

Discussion in 'Sensors and Actuators' started by davelectronic, Sep 8, 2011.

  1. davelectronic

    davelectronic

    1,079
    12
    Dec 13, 2010
    Hi all. Ive tried to find a way to control frequent start stops of a split phase induction motor, ( idea ) to use a fridge compressor for air brushing, the problem with frequent start stops is heat in the start winding, or tripping the bi metalalic thermal switch. I did not want VF control, i was looking for a more simple solution, start current is 5 amps or so, drawing air means lots of frequent stop starts in the start winding, any ideas appreciated, ive got air regulation and a reciver. Dave.
     
  2. davelectronic

    davelectronic

    1,079
    12
    Dec 13, 2010
    Split phase induction control

    what i was looking for if posable was control of the stop start actions, minus the heat gernerated in the start winding, i know the winding configerations not set up for this, but was looking for a start stop solution, that will absorbe the unwanted heat with out changing the phase angle of the winding configaration, unless its more afficiant, i now the motor charecteristics is less than perfect, but they make excelent air brush compressors, the manufacturers have it sust how do they do it ? Dave.
     
  3. davelectronic

    davelectronic

    1,079
    12
    Dec 13, 2010
    split phase induction motor control

    Hi all.
    Give it one more go, see if any one has any ideas.
    Frequent stop starts of a fridge compressor for air brushing, ( goal ) to achieve better starting torque with out over heating and staling the motor, from the thermal overload bi metallic switch.
    Any ideas appreciated.
    Dave. :)
    PS , start stops will be fairly frequently, as air receivers total is 8 liters, a pair of 4 liters diving cylinders, not wanting continuous pumping, or bleed off of air. only pressures of 25 to 30 psi needed. :)
     
  4. Resqueline

    Resqueline

    2,848
    1
    Jul 31, 2009
    There's nothing that can be done to get phase shift + improve efficiency of the start winding, but the time the motor spends in start mode could perhaps be shortened.
    But even so the run winding will take a high start current. There are two starters used for fridge motors: One is a current sensing relay, and the other employs a PTC.
    Get a relay that is meant for a little higher operating current. Alternatively remove a few windings from the present relay. With a PTC I'm not sure what to do.
    But the main path you should take is to reduce the number of starts, by means of higher max tank pressure and a bigger pressure differential (between start/stop).
    If the compressor is made for R-410a it's supposed to deal with almost 300psi, if it's made for R-12 or R134a it's not made for quite that high pressures.
    So with the regulator and pressure need you have, you could have it kick in at 50psi and out at 150 for example.
     
  5. davelectronic

    davelectronic

    1,079
    12
    Dec 13, 2010
    Split phase motor control

    Thanks for your reply Resqueline.
    I think your referring to the coolant used in fridge applications, the units ive removed have been domestic, both i could stall at less than 100 psi, G above knows what unit produces 300 psi, i am a qualified diver and have understanding of gas laws, not that i dive these days.

    The units producing over 20 bar must be industrial, ive sliced the top off one domestic unit, in hope of clues to improve start stops, removing windings would be tricky, there bound in a oil resistant nylon, if i alter the start relay turns winding, wont this maybe start it quicker, but more likely generate more heat, tripping the thermal cut off ? .

    My attempts to stall it was a finger placed over the positive pressure out put, gauge connected it stalled at about 85 psi or there abouts, i could hear it slowing, some induced pressure load and it runs, but slower, ive tried a triac dimmer type circuit, that was poor control, to slow, no pressure load, and it stalled, probably a centrifugal switch putting the start winding in circuit, yes i think your probably right, larger air receiver, and less frequent stop / starts, only charging to a max of about 60 psi, as the units max is near 80 psi, and the 25 to 30 psi i want for airbrush propellant wont give much time differential, 150 psi would be better, but the domestic units ive looked into wont get no where close to that.

    The manufacturers of these units for air brushing use the same hematically sealed units, but i guess there spec on production takes into account the duty cycle, and possibly different winding conditions for the start / stops.

    I have only pursued it for a long time as i believe there is a way round it, and a purchased airbrush pro units start at £ 350 and go up sharply.
    Thanks again for the ideas.
    Dave. :)
     
  6. Resqueline

    Resqueline

    2,848
    1
    Jul 31, 2009
    I guess R-410a is mainly used in heat pumps / air conditioners. I was unable to stall the two old R-12 (low pressure) pumps I was experimenting with in my younger days.
    The windings I were referring to is on the starter relay (in the electric connector box on the side of the compressor, that also holds the overcurrent/overtemp cutout).
     
  7. davelectronic

    davelectronic

    1,079
    12
    Dec 13, 2010
    Split phase motor control

    Yes i guessed it was them winding, to remove start or run windings would be near on impossible, would less relay start windings result in better torque start up ?, but then the start winding still has to deal with the extra heat, " bright idea moment " close circuit inter cooler, wow cracking idea, no joking, only more work and hassle, but in theory i think an idea.
    Dave. :)
     
  8. Resqueline

    Resqueline

    2,848
    1
    Jul 31, 2009
    Like I said I don't know what kind you have (PTC or relay) but the old stuff works this way:
    The start relay senses the run winding current. When the rotor is stalled this current is high and the relay pulls and engages the start winding (which draws even more).
    As the rotor picks up speed the run winding current goes down and the start relay drops out.
    If the drop-out current can be increased the start winding will be released earlier. If the motor is still able to start then all is good.
    If you'll be able to reduced this short power consumption enough to matter I can't say.
    Nothing you can do will make it better then it already is. It's all a compromise.
     
  9. davelectronic

    davelectronic

    1,079
    12
    Dec 13, 2010
    Split phase motor control

    I get what your saying, it very vague until i try it and take some current measurements, and temperatures over time, thats if i can even get the start current up a bit, but saying that i doubt as well if there will be any positive benefits, as i would be running the start winding harder, not designed for this, or the compressor, this would probably wreck the insulation and burn out, even though its only in circuit for a short time, its the way there made, for refrigeration duty cycle, not glorified compressors as i wont.

    Some times there is no fix, and i guess this is one of them times.
    Thanks again for your help.
    Dave. :)
    PS, Sorry forgot, yes relay with thermal trip.
     
    Last edited: Sep 26, 2011
  10. Resqueline

    Resqueline

    2,848
    1
    Jul 31, 2009
    The start winding is not run harder, it's the start relay being made less sensitive to the startup current.
    The start winding will be run less time, if the motor starts at all that is, it all depends on if it's run longer than neccessary as it is.
    The start relay is one item in the connector box, the thermal trip is another. Ok, so you have a relay there, that's good.
     
  11. davelectronic

    davelectronic

    1,079
    12
    Dec 13, 2010
    Split phase motor control

    Yep i will try it, its worth a go, bit like the MOT, if i don't try i cant blow it up, joke that last bit.
    Dave. :)
     
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

-