Hi
I am working on project which switches ON or OFF 220V devices for more than 2 continuous hours.
I am just confused what setup I should use.
a) RELAY & TRANSISTOR: I wonder if the current in relay coil would remain in safe limits if the coil is energized for more than 3-5 hours.
b) Or should I use TRIAC?
c) Another option is using a Solid State Relay but it is bit expensive.
What kind of devices, how much current?
Another option is using a Solid State Relay but it is bit expensive.
Not really, but beware of counterfeits and fakes. Use Google to check.
outsider:
What kind of devices, how much current?
Actually, I need to switch off a refrigerator and a deep freezer for 3-5 hours thru relay. The contact points will be disconnected when the relay coil is energized. I am concerned about the continuous current flowing thru the coil to keep them disconnected.
They will keep on running when the relay coil is not energized.
Two things to consider...
Relays will run at their rated coil voltage forever. It is no stress to the relay to stand open for hours. The only reason why you may not want to do this is power consumption: it will flatten most portable batteries very quickly.
Fridges and freezers use relatively powerful motors to run the compressors. The inductive spikes caused by these motors are quite damaging to relay contacts. Probably not a problem for you with very infrequent switching but don't buy a relay that's "only just" big enough.
Thanks for the input.
I got my answer that the relay coils can run stress-free for hours but of course will drain batteries. In my case, no batteries.
The starting amperes for the fridge and freezer are about 2A at 220AC. I intend to use relay shown in the attached picture.
abuhafss:
Thanks for the input.
I got my answer that the relay coils can run stress-free for hours but of course will drain batteries. In my case, no batteries.
The starting amperes for the fridge and freezer are about 2A at 220AC. I intend to use relay shown in the attached picture.
Buy several.
Paul
abuhafss:
Thanks for the input.
I got my answer that the relay coils can run stress-free for hours but of course will drain batteries. In my case, no batteries.
The starting amperes for the fridge and freezer are about 2A at 220AC. I intend to use relay shown in the attached picture.
The problem is the inductive nature of the load and the arcing this can cause. If the load is well snubbed
you'll probably get away with 8A relay (this is a standard rating IIRC). The surge current isn't the reason to
derate the relay, the arcing damage on switching off is.
IMO the only reason not to use a generously rated relay is size constraints, they are bigger.
Note that a relay for mains use should be wired like anything else for mains use, if you are not
confident about this get a pre-built reputable unit.
I wonder if the current in relay coil would remain in safe limits if the coil is energized for more than 3-5 hours.
And yes relays are rated for continuous duty, otherwise they'd be pretty useless. Solenoids are a whole
different game, perhaps you were thinking of them?
As a winding gets hotter the current drops, since the resistivity of copper increases with temperature,
like most/all metals.