An led across a relay coil

How do i put in an led across a relay coil to show that the coil is functioning, without the relay be triggered? I dont want to use a relay with a built-in led because that would show that the relay is function when triggered only. Please help.

erm, maybe i miss-understood the question but couldnt you just disconnect the poles on the relay? just leave the coil connected?

sparkysliderz said:

erm, maybe i miss-understood the question but couldnt you just disconnect the poles on the relay? just leave the coil connected?

Click to expand...

= I have five relays, want to show that all coils are functioning using an led for each coil, and use these signals to control a master relay. The leds should be on when you power up(assuming that the coils are working), but must not trigger the relay. It must then send all these signal to an AND gate.

There is no way to do what you describe. What you can do is have all 5 relays come on when powered and turn them off to perform the necessary actions.

I am not aware of a method, besides triggering the relay, to know it will function as needed. Even if the coil is functioning the contacts may not. Trying to verify coils are functioning prior to their use in a circuit is unncessary redundacy in most cases.

Think about it, you are basically asking how to know a switch will function before you turn it on.

IF the system requires knowing that a relay is NOT functioning then a SAFETY circuit is developed USING redundancy with devices designed for this purpose.

This site can offer information on the use of safety relays and safety interlocks. http://www.sti.com

The coil is not in fact functioning if it is not energized.

OUtputs

What are the outputs used for??

If the equipment that you have has feedback you can generate fail to start/fail to open ect you can generate these faults, and the maintenance crew can start the Fault finding procedure.

I have learnt that when it comes to a loop with a relay, that would be the first thing to check.

If you have a controller most alarming can be done using your software and minimal amount of wiring changes will be necessary.

Regards

Rheinhardt

As I understand it you want to detect if you have an open relay coil, whether the coil is energized or not.

Ok so presuming one side of the coil is grounded to a neg. or netrual side fo the main circuit power supply simply place a dropping resistor in series with an led. One the other end of the led would be connected to the signal (hot side) of the relay coil, and the other end of the resistor would be connected to the "hot" side of the main power supply. This would allow just enough curret through the relay coil to light the LED, but not enough to actuate the relay. Once you've applied power to actuate the relay coil, the led would go off.

 

* <------------power supply------------>  *

|                                         |

| n/o button                              |  

|-----*^*-------------+--(relay coil)-----+

|   resistor   led    |

+---/\/\/\/\--->]-----+

 

Exactly what size resistor to use (wattage & ohms) depends on the power supply & resistance of the relay coil (which are unknowen to me).

What about a shorted coil? Will the relay still function even though you have an led showing a path? Coils are just as likely to short as open. The contacts in the relay can weld or burn off, even if the coil will function that does not mean the relay will function?

What kind of application would use this?

rsdoran said:

What about a shorted coil? Will the relay still function even though you have an led showing a path? Coils are just as likely to short as open. The contacts in the relay can weld or burn off, even if the coil will function that does not mean the relay will function?

What kind of application would use this?

Click to expand...

None that I know of... I just answered the question I thought was being asked, but I probably should'nt have, as the only way to tell if the relay is going to function would be to inspect and test it in it's entirety at regualar intervals.

If your concerned about relay failure, try to make an educated guess as to how many operations per hour/week/month, and replace it before it reaches it's rated life cycle.

BTW, contact failure is far more comon then coil failure.

This might work for you if the relays are 24vdc. An output on the OR gate indicates that one or more relay coils are open or the relay is unplugged from the base. The 250 ohm pull up resistor should keep current low enough to not trigger the relay. This only works when all coils are off however, if any single coil is already energized, you will have an output on the OR gate, so you will not know the status of the other three coils.

This function already built in to the AB diagnostic module like 1756-OB16D. Module can detect load and short circuit.