magic electromagnet problem

Discussion in 'The Projects Forum' started by dougalere, May 4, 2015.

  1. dougalere

    Thread Starter Member

    Mar 4, 2015
    128
    5
    hi.
    finally got round to 'finishing' this pick up /drop project, works well apart from the fact that the electromagnet does not release when the power is turned off due to residual magnetism.
    i have got it to release by desensitising the poles with a bit of insulting tape but this is not entirely ideal.
    i am thinking of reversing the coil polarity at release somehow?
    any suggestions appreciated.
    thank you
    dougal
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,766
    1,099
    Post the schematic of the coil driver.
     
  3. dougalere

    Thread Starter Member

    Mar 4, 2015
    128
    5
    hi
    i have revised slightly, the coil is now at the collector,the base resistor has been replaced with a 1ok pot.
    IC2 is an op amp.
    thnk you
    doug
     
  4. dougalere

    Thread Starter Member

    Mar 4, 2015
    128
    5
    supply voltage is 4.5 volts, 9volt was found to be too high causing overheating
    L1 THE ELECTROMAGNET IS LABELLED as 1 henry, this is a typo.
    the transistor is a TIP 31
    current around 500 ma
     
    Last edited: May 4, 2015
  5. Ramussons

    Active Member

    May 3, 2013
    557
    92
    Try a 100 uF capacitor across the electromagnet. When the transistor cuts off, the resultant oscillation of the capacitor-inductance will demagnetise the electromagnet.
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,498
    2,364
    This is how it is done in most commercial lift magnets, a short reverse shot releases any load that remains attached after a lift.
    Max.
     
  7. dougalere

    Thread Starter Member

    Mar 4, 2015
    128
    5
    thank you
    i think this is solved in a roundabout way, i am using this to pick up a small nut and bolt -the holding force was fairly close to the residual force, by turning up the holding force and using a heavier nut and bolt it works perfectly, so i guess im swamping the residual force.
     
  8. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,498
    2,364
    You are probably swamping the residual force by using a reverse polarity, but you may reach the point where the residual is now reversed which then returns to the same problem?
    Max.
     
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