Simple question: if a relay on a Signal Relay Shield should be closed when power is lost, will the relay open or remain closed?
it will be in normally closed position
Can you please clarify Bhaskar? In my application, I have one of the relays wired to nomally open. When a Particle Boron application instructs it to do so, the relay closes to turn on a water pump. If, while the pump is running, the NCD relay board (and, of course, the attached Boron) loses power, I would want the relay to open so the pump does not continue running. But if I understand you correctly, loss of power will not result in the relay opening. Is that correct?
Hi @blshaw45 An SPDT relay has a common contact (C) and two contact positions: normally open (NO) and normally closed (NC). When there is no power, the common contact is connected to the NC contact. When power is applied to the relay’s coil, it creates a magnetic field that pulls an internal lever, moving the common contact (C) to the NO contact. In this position, the circuit through the NO contact closes, and the NC contact opens. When the power is turned off, the magnetic field disappears, and a spring returns the lever to its original position, reconnecting the common contact (C) back to the NC contact.
Let us know if you have any questions.
Thank you,
Eduardo M.
Many thanks Eduardo, That’s what I hoped. Our water pump is connected to common and Normally Open. So when power is lost, per your comment, common will be connected to Normally Closed which we do not use. Yippee!!