motor controller

Discussion in 'The Projects Forum' started by REHTNAP, Feb 24, 2012.

  1. REHTNAP

    Thread Starter New Member

    Feb 24, 2012
    17
    4
    hi
    as per attached circuit i know the rough idea of it being a phase splitter dimmer circuit moded slightly to drive a dc motor. what i want to know is what rolls the 2 capacitors have as a bit confused as to why 2 in the delay bit of the circuit.
    thanks
     
  2. jimkeith

    Active Member

    Oct 26, 2011
    539
    99
    R2 and C2 form a snubber network that helps the triac to latch on--also helps it to commutate (turn off) at line voltage zero crossing--typ values: 0.1uf, 150Ω.

    Vr1 and C1 form a variable phase shift network that varies conduction angle. R1 tends to 'calibrate' the active region of the pot rotation.
     
    REHTNAP likes this.
  3. REHTNAP

    Thread Starter New Member

    Feb 24, 2012
    17
    4
    thanks ive learnt something new. must read up on snubers:)
     
  4. bertus

    Administrator

    Apr 5, 2008
    15,649
    2,348
  5. jimkeith

    Active Member

    Oct 26, 2011
    539
    99
    Just noticed something--running a 24VDC motor with 115VAC or 230VAC line power using this kind of control is hard on the motor--peak current is high.

    Recommend a step-down transformer.

    A series inductor will help--the A*mH product should run in the range of roughly 100 to 200AmH
     
  6. REHTNAP

    Thread Starter New Member

    Feb 24, 2012
    17
    4
    hi
    its running from around 30v ac ish. ill put meter on it tomorrow. it runs from a tapping on a variable voltage coil that alters as the power of the coil is raised or lowered.
     
  7. REHTNAP

    Thread Starter New Member

    Feb 24, 2012
    17
    4
    hi
    the original triac is a bt138e and fails to carry current uder load is the BTA16-600B maplins sell an ok replacement?
     
  8. jimkeith

    Active Member

    Oct 26, 2011
    539
    99
    You are going from a 12A to a 16A triac--this is a step in the right direction, but I believe that you also need a better heatsink--most dimmer circuits have poor heat sinks.

    I also suspect as previously indicated that your peak current may be very high--though the average motor current may not measure high, it is the peak current that drives up the RMS current and tends to overheat power devices. You may also be close to motor demagnetization if your peak current is high--this will reduce torque and further increase the required current--not a good situation.

    Is your line voltage 115VAC or 230VAC?
     
  9. REHTNAP

    Thread Starter New Member

    Feb 24, 2012
    17
    4
    hi
    input to the circuit board is ac 27 volts. its powered from a secondary winding in one of the power coils and does raise as the power selection of the coil is increased but only up to around 33 v ac. crude but it has worked for a lot of years i think age has got to it. very temted to replace with a pwm unit powered from an individual power suply coil. the machine is uk 3 phase supplied so would have to step down to 24 v dc to drive the motor.
     
  10. REHTNAP

    Thread Starter New Member

    Feb 24, 2012
    17
    4
    another question
    the BTA16-600B is described as snubless so should i remove the snubber or will it not affect it if i leave it in place.
    there is a finned heat sink on the board the triac bolts to i may increase its size to aid the triac cooling.
     
Loading...