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I'm just confused about relays. For example, say for something like this https://uk.rs-online.com/web/p/latching-relays/0515571/ It says coil voltage is rated for 12VDC and switching current of 5A. Does that mean that to close the relay (turn power on), I have to apply 12VDC across two of it's terminals and as soon as that 12VDC is gone, it turns off? Or does that mean, I have to apply 12VDC to turn it off?
Also, what does the switching current mean?
That particular relay is a dual coil latching relay. You would apply a short pulse of 12 V to one coil to set the contacts in one position, and a similar pulse to the second coil to set the contacts to the other position.
Under "contact rating", the datasheet states that the contacts are rated to carry 2 amps - I don't know where the 5 Amp rating in the feature list comes from...
For normal (non-latching) relays, you apply power to move the contacts to the "normally open" position, and remove power to allow the contacts to return to the "normally closed" position.
