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Number of turns in Electromagnet for Relay

Discussion in 'Robotics & Mechatronics' started by koolguy, Oct 26, 2015.

  1. koolguy

    koolguy Active Member

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    Hello,
    How to calculate Number of turns in Electromagnet for Relay .
     
  2. alec_t

    alec_t Well-Known Member Most Helpful Member

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    That's like asking "How long is a piece of string?" ;). We're not psychic. What are the relay specifications (closing force, spring constant, pole-to-armature spacing, core permeability, required field strength, coil resistance, coil volume, power consumption, operating speed ....)?
     
  3. koolguy

    koolguy Active Member

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    i just open a ready made relay, so no idea of specification.
    but is there any formula to know number of turn to be there in electromagnet relay.
     
  4. dave

    Dave New Member

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  5. Pommie

    Pommie Well-Known Member Most Helpful Member

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    Find the resistance (from datasheet) and diameter of wire (by measurement). Use resistance to calculate length (or weight) required. Wind required amount on relay.

    Mike.
     
  6. DerStrom8

    DerStrom8 Super Moderator Most Helpful Member

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    You don't seem to grasp that there are literally millions of different types of relays, different specs, different operating modes, different operating methods, etc. No single formula can be used to design every possible type of relay.
     
  7. MaxHeadRoom78

    MaxHeadRoom78 Active Member

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    Also required is the effort required for full attraction of the armature.
    Max.
     
  8. Pommie

    Pommie Well-Known Member Most Helpful Member

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    There is no need to redesign the relay, just to work out how to rewind the coil.

    Mike.
     
  9. koolguy

    koolguy Active Member

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    How to measure the diameter of small wires coil?
     
  10. alec_t

    alec_t Well-Known Member Most Helpful Member

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    Micrometer.
     
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  11. koolguy

    koolguy Active Member

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  12. JimB

    JimB Super Moderator Most Helpful Member

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  13. koolguy

    koolguy Active Member

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  14. Colin

    Colin Member

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    Just wind 30 turns on a rod and then get other wire and wind 30 turns and see if the length is the same.
    No dial-micrometer needed. Just intelligence.
     
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  15. DerStrom8

    DerStrom8 Super Moderator Most Helpful Member

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    And an excess of wire, as well as a wide selection in order to find the proper gauge. This is by far the least efficient option.

    Just pay $35 for a micrometer. It'll come in extremely handy down the road for a wide variety of projects.
     
  16. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi,

    Go out and purchase a new relay. That gets you there faster and without any measuring or what have you.
     
  17. Colin

    Colin Member

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    There is one underlying fact that no-one has brought up and no text book has covered.
    I wrote it up recently while covering the impedance of a speaker.
    8 ohm speakers are expensive and 50 ohm speakers are cheap because no-one thinks you can substitute the two.
    So you can pick up 50 ohm speakers for almost nothing.
    When you test them in an amplifier, the output is almost the same.
    The reason is a speaker works on the principle of AMP-TURNS.
    The magnetic flux produced by the coil interacts with the permanent magnet to move the cone.
    The multiplication of the number of turns on an 8 ohm coil and the current delivered by a circuit to drive it, it almost the same as the number of turns on a 50 ohm coil and the current.
    The same applies to a relay.
    It relies on AMP-TURNS and the space inside a relay can be filled with thick wire or thin wire to produce the same result and thus the wire-size can be anything.
    As long as you fill the bobbin, the relay will activate.
     
  18. alec_t

    alec_t Well-Known Member Most Helpful Member

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    That may be true, but is also inconvenient if you have a fixed voltage supply for other components in a circuit. If, for example, most components required 5V, then a standard 5V-rated relay drawing 40mA would be more convenient than an arbitrarily wound one whose coil needed 400mA at 0.5V to operate.
     
  19. Pommie

    Pommie Well-Known Member Most Helpful Member

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    So, simples then. One turn of very thick wire will do it. Shame my pic can't deliver the 150A required.

    Mike.
     
  20. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi,

    As others have already noted, there is one more small detail. It is true that the relay itself works more or less like that, but we also have to match the coil up with what we have to drive it with.

    Usually that extra detail is the resistance. The coil is wound with the chosen wire size and number of turns and core material so that at the chosen voltage the current is right to pull the relay arm in toward the coil, and without drawing excessive current from the power supply. Thus a 5v relay can be different than a 10v relay with the same contact size. The 10v relay can use smaller wire so that the coil does not draw too much current, and thus the power consumption of the coil stays the same.
     
  21. DerStrom8

    DerStrom8 Super Moderator Most Helpful Member

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    Hi all, I just wanted to point out that the OP is no longer a member here.
     
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