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Discharge circuit in electric vehicle

  1. Mar 14, 2014 #1
    we are designing a electric car. in that motor controller has capacitors which get charged when supply is given.so across the contactor we are attaching a precharge resistor,which prevents the hiigh inrush of current in motor controller. now we are stuck on the ques that how to discharge the capacitors? what is a discharge circuit?
  2. jcsd
  3. Mar 14, 2014 #2
    A circuit diagram of what you have so far would be helpful.

    In general you can connect a resistor in parallel with the capacitors to discharge them. There will be engineering concerns with the value of the resistor. It will have to be high enough so that you are not wasting power by running a high current through it but also not so high that it takes too long to discharge the capacitor. It all depends on your application. Look up RC circuits to see more on that.

    It's also pretty common to use diodes to discharge capacitors in voltage regulators and motor drivers. A circuit diagram would be needed to see exactly what your application does and where a diode might be appropriate.

    When you say contactor are you talking about an electro-mechanical relay? That would not be a good choice for a variable speed motor application like you might have in a car. A solid state device would be much better. The reason is that you typically control the duty cycle of a DC motor to regulate its speed and torque. An eletro-mechanical relay doesn't switch quickly enough or reliably enough to do this properly. The contacts in a contactor also wear out over time from electrical arcs.
  4. Mar 14, 2014 #3
    The concept in vehicles is often to make a mechanism that connects a discharge resistor - before the access to the capacitors ( or batteries) is allowed.

    Usually just discharged through a resistor. For example - you can use a screw in a cover plate to press a limit switch, as the screw is removed the switch closes completing the circuit through the discharge resistor.

    Oh... in industrial systems the Resistors are sometimes left on permanently, and may have a 5 minute discharge time, and be labeled as such. IN the Vehicles they care more about efficiency and want a faster discharge - so a different solution is used.
  5. Mar 15, 2014 #4
    circuit diagram

    this the circuit diagram.please refer and help me how to discharge the capacitors in controller

    Attached Files:

  6. Mar 16, 2014 #5
    Can you add a NC contact to the key switch? ( i.e. the the key is off or removed, the contact is closed?)
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