Solenoid

Discussion in 'General Electronics Chat' started by phuzionz, Dec 22, 2008.

  1. phuzionz

    Thread Starter Active Member

    Dec 5, 2008
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    Do somebody know more about solenoids?
    I have a pressure regulator solenoid, and the manufacturar suggest to drive this with a lower PWM frequency. This can improve the hysteresis problem.
    Have somebody from you already deal with that problem.

    How can a lower PWM frequency solve that problem.

    Jef
     
  2. PRS

    Well-Known Member

    Aug 24, 2008
    989
    35
    I'm not familiar with your particular problem. But PWM is a means of varying the power available to the load. Instead of just raising or lowering a voltage -- the usual method of varying DC voltage, hence current and power -- you accomplish the same thing by sending DC voltage in spurts that last a certain amount of time as determined by the PWM circuit. The longer the spurt the more the power, the shorter spurt the less power. This varies the power applied to the solenoid.

    I'm not sure what the hysteresis problem is, but this is how PWM works.
     
  3. DrNick

    Active Member

    Dec 13, 2006
    110
    2
    They are referring to hysteresis losses in the core of the solenoid. As the frequency of the excitation in any magnetic system increases, more eddy currents are induced in the core. Heating and loss come with eddy currents. Therefore, to avoid excessive heating and unnecessary losses, a lower frequency PWM is suggested.

    One other advantage of PWM control of the solenoid is, you can drive high duty cycle when actuating the solenoid, and then reduce the duty cycle to provide the minimum current required to keep the switch/plunger at its desired position. This will allow you to consume less power under steady state operation.
     
  4. PRS

    Well-Known Member

    Aug 24, 2008
    989
    35
    On the money (nt)
     
  5. phuzionz

    Thread Starter Active Member

    Dec 5, 2008
    47
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    Thank you for the anwers.

    @DrNick
    I try to understand the relationship between the PWM frequency and the eddy currents induced in the plunger of the solenoid.
    Can you help to understand it better?

    Jef
     
  6. phuzionz

    Thread Starter Active Member

    Dec 5, 2008
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  7. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,348
    Hello,

    Perhaps this link in the wiki will say someting more :
    http://en.wikipedia.org/wiki/Eddy_current

    Strength of eddy currents

    Some things usually increase the size and effects of eddy currents:

    • stronger magnetic fields
    • faster changing fields (due to faster relative speeds or otherwise)
    • thicker materials
    • lower resistivity materials (aluminium, copper, silver etc.)
    Some things reduce the effects

    • weaker magnets
    • slower changing fields (slower relative speeds)
    • thinner materials
    • slotted materials so that currents cannot circulate
    • laminated materials so that currents cannot circulate
    • higher resistance materials (silicon rich iron etc.)
    Greetings,
    Bertus
     
  8. phuzionz

    Thread Starter Active Member

    Dec 5, 2008
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    So when you use a PWM frequency you get normally an average current, but the solenoid sees that really as an ON/OFF operation. Due to rapidly changing the flux, more eddy currents are induced.

    So normally i use a frequency of 1Khz, but when i use 400Hz, does that mean that my OFF period is longer?
    And i can also make my lower frrequncy with a longer and shorter ON period, but it stays 400Hz, can that also affect the eddy current?

    Jef
     
  9. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,176
    397
    If the ratoi of on to off stays constant average power should stay the same neglecting losses.Can you feel any difference in plunger temperature at different frequencies?
     
  10. phuzionz

    Thread Starter Active Member

    Dec 5, 2008
    47
    0
    Sorry, I am not be able to test that because i'am now in a syage to select a solenoid according some requirements.

    One of these is a lower PWM frequency.

    Jef
     
  11. phuzionz

    Thread Starter Active Member

    Dec 5, 2008
    47
    0
    Hello,

    I'am struggling a quite long time with this, without any result.
    Can somebody tell me the relation between eddy currents and PWM frequnecy.
    I know what eddy currents are, it is already posted in this topic, but the explenation behind it, i can't find it.

    With faster magnetic fields, you get more losses due to the eddy currents. This statement isn't clear for me.

    Thank you,
    Jef
     
  12. phuzionz

    Thread Starter Active Member

    Dec 5, 2008
    47
    0
    Can nobody help me with this issues? pushing me in some direction is also good

    Jef
     
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