Relay isn't NC nor NO

Discussion in 'General Electronics Chat' started by nikolasj5, Jul 4, 2013.

  1. nikolasj5

    Thread Starter New Member

    Jul 2, 2013
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    Hi everyone,

    I have two relays controlling two independent parts of the circuit. And both coils are in parallel with a 5V generator (sufficient for this relay).

    But what i can't understand is that one relay switch from NC to NO and works fine while the other isn't neither in NC nor in NO! I've tested them and they are ok, the problem happens when they connected together.

    Is it something common to happen? Where should i start looking for a solution?

    Thank you :) !
     
  2. LDC3

    Active Member

    Apr 27, 2013
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    Are they connected in series or parallel? Does the second relay oscillate between positions?
     
  3. nikolasj5

    Thread Starter New Member

    Jul 2, 2013
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    They are in parallel, and the second doesn't oscillate. And i just have to turn the 5V on and keep it on forever.
     
  4. LDC3

    Active Member

    Apr 27, 2013
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    What are the current requirements for the relays and what is the available current from your supply? Are there limiting resistors in series with the relays?
    If you post a diagram of your circuit, it might help.
     
  5. nikolasj5

    Thread Starter New Member

    Jul 2, 2013
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    I've bought it in a local store and the only datasheet i've found was this one(horrible!):
    http://pdf1.alldatasheet.com/datasheet-pdf/view/114955/ETC1/JQC-3F.html

    My supply is a Arduino Mega 2560 wich has a limitation of 200 mA in VCC pin.

    I'll do a schematic here (don't have one yet, sorry...) but the VCC is connected only with the relays. the GND have connections with other IC but their supplies aren't the same VCC.
     
  6. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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  7. nikolasj5

    Thread Starter New Member

    Jul 2, 2013
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    Hum! Thanks!

    Made a test here with some resistor in parallel so they consume current. When it got in a current lower than the specs both relays just didn't change status. Both stayed in NC. Does it make any sense?
     
  8. SSR

    New Member

    Aug 6, 2011
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    Seems like the current falls short to drive both the relays.
     
  9. WBahn

    Moderator

    Mar 31, 2012
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    That's the maximum amount that the Arduino as a whole can/will/should draw. It is NOT the maximum current that cen be supplied by an output pin. Based on some of the other Arduino threads, that seems to be something in the 50mA range.

    I suspect that what is happening is that your two relay coils have sufficiently different resistance such that one of them gets enough current to pull-in but the other doesn't when the Arduino ouptut voltage falls to a point that the current draw equilibrates. At 70Ω each coil is nominally wanting 70mA to operate. It will actually pull-in at something less than that. Similarly, the Arduino will probably actually supply something more than 50mA. But it would not be surprising at all for the output not to be able to drive two coils.


    Try using a transistor to buffer the Arduino from the coils. And be sure to put in anti-kickback diodes across the coils.
     
    nikolasj5 likes this.
  10. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    I wouldn't begin to guess at the problem until I saw a schematic.

    While I suspect a language translation issue in this thread a schematic works in any and all languages.
     
  11. nikolasj5

    Thread Starter New Member

    Jul 2, 2013
    6
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    Guys, my relay was broken... Because of this one was working properly while the other not.

    Thanks a lot for all the replies, i will use a transistor for buffering and a anti-kickback diode as suggested. Thank you very much!
     
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