Hi
In my project I need to use relays to turn off certain items when needed but most of the time they would be running 24 hours a day 7 days a week continually.
Is it safe to have a mechanical relay energised constantly or will its coil burn out?
Would a solid state relay be better?
Any help would be great!
Thanks
Review the datasheet for the relay in question, see if it has any limits on how long the coil can be energized. There is often a lifetime limit on how many actuations the contacts are rated for.
Yes, you can power a relay indefinitely.
If you use solid state relays, make sure it's "properly rated" for the voltage & current you're switching. i.e. AC & DC solid state relays are not interchangeable and some AC power-line solid state relays won't work properly with low AC voltages, or a solid state might "leak" some current so don't work well with low currents.
If you are switching the power line [u]these industrial type[/u] solid state relays are super-easy to wire up with screw terminals, super-easy to mount, and some can be driven directly from the Arduino.
Can you describe what these relays will be switching?
If the relay is to be in one state most of the time and the other "some" of the time, you might consider going with a relay that has NO and NC contacts and configure your setup so the action required less of the time is the one that requires energizing the coil.
FWIW, properly sized and operated in an environment that respects the thermal and power ratings of the relay I doubt you would ever have reliability problems with the coil. The main contacts are more likely to the be the problem in the long run.
You might also look at the ratings for the relay coil: With a 12V coil, for example, you might find that the relay will be guaranteed to "pull in" at, say, 9V but will release as low as 2V. If you find you need to have the relay energized a long time, maybe think about a way to "peak and hold" the coil (large initial voltage to pull it in and then reduce voltage & current to hold it there...)
Of course, an all-important aspect not mentioned so far in this completely inadequate description, is the "fail-safe" condition. 