Inductor

Discussion in 'General Electronics Chat' started by Dritech, Dec 6, 2012.

  1. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
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    Hi,

    Can someone please explain to me what would be the positive and negative effect on the functionality of contactor (which is formed from R3 and the inductor) if R2 is increased?
     
  2. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
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    The only thing i know is that it will only be affected during discharge since R2 is connected to switch position 2. Any help please?
     
  3. #12

    Expert

    Nov 30, 2010
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    You've got me stumped. What would be the positive and negative effects on a light bulb when you turn it off and have a resistor in parallel with it? Wouldn't that be like having 2 light bulbs operated by one switch?
     
    Last edited: Dec 6, 2012
  4. WBahn

    Moderator

    Mar 31, 2012
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    If R2 is increased the the following will result:

    The voltage across the inductor just after the switch changes from R1 to R2 will increase because you will have the same current flowing through a higher resistance.

    The time constant for discharging the inductor, which is L/(R2+R3), will decrease so the inductor will discharge quicker. Assuming this contactor uses the field from the inductor to move the contacts, that could mean quicker and cleaner disengagements.
     
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  5. #12

    Expert

    Nov 30, 2010
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    Thanks.

    I'd like to say this has no practical application. I've worked on thousands of machines with contactors in them and not one had a resistor to help it open quicker. They all rely on the spring that is inside them to open the contacts.

    Dritech: Where did you get the idea for this question?
     
  6. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Several companies I've worked for have sold hundreds of thousands of modules that go across relay coils to make then open quicker. OK, they don't use resistors but a zener and a rectifier diode (where the zener provides the large turn off voltage) but it's quite common.

    However, since relay manufacturers place these things inside the relay housing you could have used them but never ever seen one.
     
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  7. #12

    Expert

    Nov 30, 2010
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    True. I've never seen one. Most of the contactors I have seen look like their coils are a coil of copper wire connected to 2 spade terminals. Some of them have what looks like a cloth wrap on the coil. Could it be because I almost never work anything higher than 50 amps? Could it be that the relays that work below 10 amps actually have a case that I can't see into and they have the quenching circuit?
     
  8. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
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    Thanks for the help ;)
     
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