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I have built the above circuit. The relay switches once, but then stops. Why does this not oscillate, as the current is broken every time it connects?

  • 1
    \$\begingroup\$ It should - assuming reasonable actual values. The LED will never light. How about some more information? \$\endgroup\$ May 1, 2015 at 19:34
  • \$\begingroup\$ Probably oscillating so fast that you can't hear/see it. The contacts will barely open. It might whistle is you listen closely. By the time the contact start to open ever so slightly, the relay immediately de-energizes. \$\endgroup\$
    – jippie
    May 1, 2015 at 19:39
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    \$\begingroup\$ In which position does it stop? \$\endgroup\$
    – Eugene Sh.
    May 1, 2015 at 20:22
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    \$\begingroup\$ 1V won't drive a relay or a LED. Given this part of the circuit is wrong how can anyone have confidence that you have wired it up correctly? Detail is darn important!! \$\endgroup\$
    – Andy aka
    May 1, 2015 at 20:55
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    \$\begingroup\$ @efox29 Sure, if the contacts are not in series with an inductor, there's no need for a flyback diode to protect them. There may still be a need for a flyback diode across the coil if there's something switching the coil current on and off that can be damaged by a large voltage spike, and there may be a need for a flyback diode across an inductive load to protect the contacts, but otherwise the contacts are safe from arcing. \$\endgroup\$
    – John D
    May 2, 2015 at 1:52

1 Answer 1


There are several possibilities as to why the relay does not oscillate: 1) If the LED lit once, then the battery gets discharged after the first actuation and therefore can't repeat the activation. 2) The relay contact IS oscillating, but you can't detect it (too high). 3) The battery does not have sufficient voltage to "completely" break the circuit, but you "hear"the relay click once.

To give you a more precise answer, I need to know the relay specs, the battery's power capability, and what is the LED doing (full brightness, dull, off)?


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