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Field Failure

Discussion in 'General Electronics Discussion' started by Bremme, Nov 1, 2016.

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  1. Bremme

    Bremme

    10
    0
    Oct 6, 2016
    I have a seperately excited electric motor (D&D 14 hp continuous) and I wish to avoid feeding the armature if there is no current at the field. So, what would be the best way to cut off the armature current if the current at the field ever stops. The range of the field amps goes from a minimum of 5 A to a maximum of 50 A. I use field weakening as a limited speed variation. Since the motor starts with no load, the amperage at the field could go down to 2 or 3 amps but it should never be absent because the armature would then be shorted.
    I have a Current Sensor (DFRobot 0098) which gives me 40mV/A. At 5A this results in 200 mV (and 2V at 50A).
    Thank you for your advices.
     
  2. Minder

    Minder

    3,013
    640
    Apr 24, 2015
    The main problem with the field going open circuit when running is it will take off, rpm wise and a chance of flying apart.
    This is why wound field shunt motors have some kind of current detection in order to avoid this.
    If you want to make use of the current sensor you could use a level detection in the form of a Mosfet and then a LM311 comparitor to shut down for any current below 5a.
    M..
     
  3. Bremme

    Bremme

    10
    0
    Oct 6, 2016
    Thank you for your help. I appreciate.
     
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