I want to operate a DC brake for crane hoist - KBPC3510 rectifier

Discussion in 'General Electronics Chat' started by PRAVEEN SHARMA, Jan 9, 2016.

  1. PRAVEEN SHARMA

    Thread Starter New Member

    Jan 1, 2016
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    Mods edit:
    This thread was split form -- Full bridge rectifier.
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    Hi everyone,

    I want to operate a DC brake for crane hoist. Brake rating is 24V DC, 80W rating max. Can i use [​IMG] KBPC3510 rectifier. What AC voltage transformer to be used. how much VA rating to be used. Please help KBPC3510-3510-35A-1000V-Bridge-Rectifier.jpg
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Measure the resistance of the brake coil and this can then calculate the VA required.
    A transformer va from your numbers is around 100Va.
    24vac secondary, no Cap required.
    Max.
     
  3. Papabravo

    Expert

    Feb 24, 2006
    10,138
    1,787
    Transformers are labeled for AC voltages which are RMS (Root Mean Square). Given an RMS voltage, you multiply that by the SQRT(2) ≈ 1.414 to get the peak voltage. You need a little bit of headroom for the diodes in the bridge rectifier and a bit more if you want to use a voltage regulator.

    So:
    24= \sqrt{2}V_{ac} - 1.4
    \left(\frac{24 + 1.4}{\sqrt{2}}\right)=V_{ac}
    V_{ac} \approx 18 \text VAC_{rms}

    If you want to use a voltage regulator then bump the AC voltage up a bit to say 20 VAC.
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    For a brake you do not need smoothed DC, place a reverse diode across the brake help retain it.
    Max.
     
  5. chuckey

    Well-Known Member

    Jun 4, 2007
    75
    10
    Depending on how the DC is being switched to the brake, it would be worth while to incorporate a back EMF diode or some sort of snubber across the switch.
    Frank
     
  6. panic mode

    Senior Member

    Oct 10, 2011
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    you definitely need a diode across brake and this needs to be placed as close as possible to the brake coil (not 30m away or where PSU is). note, this diode need to be reverse biased (cathode to +ve side).

    24VDC is industrial standard and you don't need to make own PSU, you can get cheap industrial PSU which will have approvals and other features that may be useful (like short circuit protection etc).

    if you are making your own PSU, yes you can use that bridge rectifier, with up to 1000V and 35A it is more than big enough (an overkill actually - something rated for 60V and 5A would also be fine).
     
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
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    He already has the bridge, and 24vac control transformers are common.
    Max.
     
  8. ian field

    Distinguished Member

    Oct 27, 2012
    4,413
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    Crane hoists usually use DC braking.

    2 push buttons for up and down. each button is single pole changeover. both buttons pressed or both buttons released shorts the motor winding.

    Just to get started - say both NC contacts go to battery negative, and both NO contacts go to battery positive. the motor is strung between the to moving contacts. Any time both switches are in the same state; both ends of the motor winding are connected to the same battery terminal.
     
    Last edited: Jan 10, 2016
  9. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Doesn't help the OP, he evidently has a 24VDC 80w brake to operate. Could be a 1ph or 3ph motor.
    Max.
     
  10. crutschow

    Expert

    Mar 14, 2008
    13,000
    3,229
    Actually, you do want the diode at the PSU switch so it suppresses the spike from the wire inductance as well as the brake inductance.
    Remember that the purpose of the diode is to provide a path for the inductive current when the switch opens, and that path includes the wire inductance.

    But if you switch the AC voltage to control the brake then you don't need any added suppression diode since the bridge diodes will serve that purpose.
     
  11. panic mode

    Senior Member

    Oct 10, 2011
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    you can have both but if one must choose, imho it is better to have diode at the load. otherwise you are burning contacts and stressing insulation of the wires and load.
     
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