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Relay question

  1. Jul 27, 2011 #1
    Last edited by a moderator: Apr 26, 2017
  2. jcsd
  3. Jul 28, 2011 #2
    According to the data sheet's first page, it's the rated DC load voltage. That particular switch can operate from 16.8 V to 61.2 V DC at the load.
  4. Jul 28, 2011 #3
    actually i'm building a circuit as so, it uses a 555 timer to control the relay.
    i've done the simulation and it works out fine but when applying it in a real circuit board.
    the result are not the same as simulated.


    can anyone give me any advice regarding this?
  5. Jul 28, 2011 #4


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    Welcome to PhysicsForums!

    What sorts of results are you getting?

    My 555 is a little rusty, so on the assumption that you're doing an astable, what's your frequency and duty cycle? If it's too fast, or too low of a duty cycle, the relay won't be able to switch.

    Additionally, the power consumption with DC is 0.4 - 0.48 W--assuming that you're using 17V (B1), that's between 23 and 28 mA. I don't believe a 555 is capable of driving that much current.

    And lastly, if the LED does light up initially, but stops soon thereafter, you probably need a ballast resistor to control the current going to it (unless it's designed for 24V operation and already has one inside).

    EDIT: BAH! You're actually using an NPN to drive--no more late night circuit analysis for me...
  6. Jul 28, 2011 #5
    The result are not same? What are the differences.
    Place an Led in series with 1K resister directly at the output of 555 Timer. That way, you can quickly know whether it is the relays fault or the 555's. By the way, 555's are rated for magnificent 200ma, so you may not require any transistor at all.
  7. Jul 28, 2011 #6
    i've tested that using a LED, and it keeps on lighting forever =(
    the timer should be 40sec on , 4 sec off. but not sure why.
    might have fried my 555timer when i hook it up to a 17VDC power source.
    i'll get a new chip and try it again.

    as for the transistor, i've actually took this from a internet source, still learning my electronics , not my major thou
  8. Jul 28, 2011 #7
    Yeah, Fried 555 might be the reason. Is it hot to touch?
    I think 555 is rated only for about 15 Volts , so you should better use regulators such as common LM7812 for power supplying the 555.
    Don't take out the transistor, its necessary here because the relay needs higher voltage (24V) to operate than that 555 is getting (12V).
  9. Jul 28, 2011 #8
    its funny, if i reduce the first resistor which is R1 to a smaller value it works.
    which is from 3Mohm to around 50kohm,

    is it possible that both of the resistor must not differentiate too much ?
    or is there a limit for the timer?

    edit: i might found my error, seems like there resistor can only be from 1k to 100k omh ...
    does any timer support a much larger ohm ?
  10. Jul 29, 2011 #9
    Yeah,if you use resister larger than 1Mohm, then the reliability is reduced.
    So, you better replace that 3Mohm resister with 300 kohm and switch the 10uf Capacitor to 100uf. You will be fine.

    The two reister can be different, no problem there.
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