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How can I determine the maximum allowed time a relay coil can be energized?
I'm only assuming that it would get too hot eventually and damage the insulation or am I on the wrong track?
A example is this Phoenix Contact relay which I will be using in an upcoming project.
It would be a very poor relay which had a "maximum operate time".
Many relays in an industrial environment are energised continuously from one year to the next.
The only time they will be de-energised is during maintenance or emergency shutdown situations.
Just don't exceed the voltage rating of the coil and it will be fine.
This is why I tend to only use DC relays, contactors and solenoids.
If something deters them from moving the armature over, they do not tend to burn out or fail as can happen with the AC version!
Your concern only happens with AC.
Max.
That is not true with a lot of 24V DC industrial contactors! Many have a two-stage coil, either tapped or double wound, with a break contact that operates just as the armature closes to disconnect the high current coil or add in the low current one in series..
As the current with a DC solenoid is not naturally higher with an air gap in the magnetic circuit (as it is with AC), the pull-in force and coil power needed is far above the hold-in power with no or minimal air gap. They need a higher powered boost to get the armature near seated before the holding coil can provide enough sustaining force.
Some newer ones use electronics in the "coil" module and/or permanent magnet bias to provide pull-in power, but older design ones are still often two stage.
Where I used to work we had a large 240V AC contactor that supplied the power to the workshop, so at night you simply flicked a small switch and everything you wanted OFF went OFF. This was installed after we had a fire, caused by a TV that caught on fire during the night - the set had failed while on test, so no one turned it off as we left, as no one realised it was still on.
The new contactor automatically turned everything off, so no such worries once that was fitted. There was also a second identical contactor, that supplied powe to the night store heaters, fed from a time switch.
However, both had a tendency to buzz quite loudly, and we used to hit them with a brush handle to try and quieten them down (they were fitted quite high up).
They didn't use any 'pull in' or 'hold in' design, just a simple coil - I suspect a more modern one probably wouldn't have buzzed?.
I realize there are dual col DC contactor coils, but In my experience in the control industry, they are few and far between.
The AC contactor armatures now have a shading ring which is used to help prevent the buzz.
On the question of difference, I had alot of push back from N.A.suppliers on the question of specifying DC solenoids.
Where I came from (UK) we mainly used DC relays/solenoids where possible and seldom had failures.
So I naturally spec'd them in on new installations.
The companies that I converted assembly line control to PLC had a long history of down time due to failure of AC solenoid coil failure, as reflected in the spares dept.
Often the failure was due to mechanical maintenance personnel pushing an engaged solenoid valve over manually in order to trouble shoot.
Result, burn out of the coil.
The only time the AC solenoid/coil has the edge is pull in time, after that the DC is superior.
Max.
How can I determine the maximum allowed time a relay coil can be energized?
I'm only assuming that it would get too hot eventually and damage the insulation or am I on the wrong track?
A example is this Phoenix Contact relay which I will be using in an upcoming project.
To reiterate, as the thread has drifted somewhat - the relay is perfectly fine for continuous use, as almost all relays are (and particularly this one, as it's specifically intended for continuous professional use).
How can I determine the maximum allowed time a relay coil can be energized?
I'm only assuming that it would get too hot eventually and damage the insulation or am I on the wrong track?
A example is this Phoenix Contact relay which I will be using in an upcoming project.
If there is a version of that relay that has an additional n.o. contact, you could energize it at operate current, then latch it at reduced current through a resistor and the n.o. contact. The 24V DC type relays will last many (1000s) of hours. We used to use them this way in RR traffic control systems back in the day..
AV receivers use 12V relays that remain on all the time the unit is on... relays are designed for "100% duty cycle" applications. only mistakes like running them over rated coil voltage shortens their life. a relay would be kind of useless if it had duty cycle limitation. if absolute reliability is required, be aware that you can use slightly reduced coil voltage and the relay will still reliably pull-in..
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