Is it possible to force a relay to toggle without changing the input to the coil? i.e. if the relay (a sealed SPDT, say) has 0V on the coil such that NC is connected, it is theoretically possible that a REALLY HUGE magnetic field could force the contact to the NO position.

How likely is this is a typical environment? Are there any relays which quote this theoretical value?

Are there any other ways this condition could be forced (or reversed)?

  • 1
    \$\begingroup\$ Vibration potentially can momentarily change the output state, and there may be vibration specs on some relays. \$\endgroup\$ – Brian Drummond Nov 18 '15 at 21:42
  • 1
    \$\begingroup\$ "REALLY HUGE magnetic field" can cause many funny things happen. \$\endgroup\$ – Eugene Sh. Nov 18 '15 at 22:04
  • \$\begingroup\$ @BrianDrummond, fair point, but I was thinking more 'permanently' \$\endgroup\$ – agentroadkill Nov 18 '15 at 22:08
  • \$\begingroup\$ Is this an "I was just wondering" question or have you an application? If so, can we have the details? Since most relays' armature forms a loop I suspect that nearly any magnetic field would cancel out in the two halves of the loop unless it was right beside one side of the core. \$\endgroup\$ – Transistor Nov 18 '15 at 23:43
  • \$\begingroup\$ @transistor, this is more of a "I was playing with a relay and had a thought" question. Rather than putting on some rubber gloves and getting a neyodium magnet, I thought I'd ask here C= \$\endgroup\$ – agentroadkill Nov 18 '15 at 23:46

A reed relay will do this -- you'll commonly see these on home security systems to detect window or door openings.

| improve this answer | |
  • \$\begingroup\$ Right, but wouldn't those be triggered by a change in voltage on the coil? \$\endgroup\$ – agentroadkill Nov 19 '15 at 15:34
  • \$\begingroup\$ Sufficient current flowing in the coil, or an external magnetic field will move the contacts. If you don't want the coil to activate the relay, then what's the purpose of the coil ? \$\endgroup\$ – jp314 Nov 20 '15 at 5:57
  • \$\begingroup\$ I do want the relay triggered by the coil, I'm looking for other things that could do that \$\endgroup\$ – agentroadkill Nov 20 '15 at 6:37
  • \$\begingroup\$ I bet a spark from a high voltage could blow apart the NC contacts, making momentary contact with the NO contacts. I saw an automobile mechanical clock that worked this way... every time the spring reached the unwound position, a contactor on the end touched an energized contactor. The resulting spark was sufficient to reset the spring and keep the clock running. Really weird design... \$\endgroup\$ – Ryan Griggs Dec 19 '15 at 4:10

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.