Mechanical Relay Not Functioning When Apply Voltage?

[Unregistered]

Hi,

Dear experts in this website. I have a doubt. I encountered a normal mechanical relay(omron MY4N) not functioning when applying the DC24V. I used multi-meter to check it and the DC24V is across that coil but it never turn on the relay. I change a new one and it works.. May I know where could it be the trick?

I last time also encountering DC24V applying to a normal valve and it is not functioning. Change a new one and it works. The suspect faulty valve send back to its own manufacturing company and verify that the valve is 'functioning properly' and they ask me how i connect my circuit. I just know I connect as per normal only. Where could it be the trick again here...

Hope you all can find out the 'tricks' for me. Thank you.

 

[elevmike]

Did you check the resistance of the coil? Likely it's an open coil. Happens all the time....

 

[Unregistered]

Hi mr Elemike,

I off duty now. Maybe I can check tomorrow. Then how to explain the valve that I encountered last time. It was sent back to the manufacturer and they mentioned the valve is in a good condition and they ask how I connect the circuit. But then, I measured the voltage across the valve and the multimeter does show DC24V. Sometime, I also run out of idea.

See maybe you or someone else can find out this trick... Thanks a lot for the reply.. Thank you...

 

[Unregistered]

Oooops,

Sorry for my wrong typing... is mr ELEVMIKE instead of elemike... sorry...

 

[Tom Jenkins]

Often relay failures are not 100% functional to 0% functional. Often perfect operation is followed by intermittent operation which eventually becomes never works.

Does the coil have an LED or mechanical indicator that shows the coil is actually pulling in? I prefer that type for trouble shooting. As Mike said, voltage at the coil may not mean the contacts pull in and change state.

I would guess that the coil was OK, but you had contacts that were going bad. The contact may "open" and "close" but if they are pitted or corroded you may not have enough conductivity to get the full voltage and current to the load. At other times the contacts hit just right and you get enough conductivity to operate the load. Bad contacts are very often the cuase of intermittent relay failures.

 

[Hydro Power Guy]

Are the contacts suited for the load they are switching? You need to check the voltage and current relay specifications against the load requirements. You may find that you are switching a very low current with a standard relay that is not rated for the low current application.

 

[JIMMY-S]

Did you check the relay base. I've had a lot of older bases with lose connections on the pins.

 

[Wilcotton]

Unregistered Guest.

Don't know any tricks, but, keep in mind that it is the current through
the coil that "turns on" the relay, not the voltage at the relay. The
current path can be disrupted by a relay pin not properly seating in the socket,for instance. I've had situations where I had one relay working
and one not working and simply swapped one with the other and presto,
they both worked. Not a permanent cure but a quick temporary fix.

Keep Kurrent,

Wilcotton

 

[Unregistered]

If you measure 24V volts across the coil that means that the coil is "open".
When the coi is good and you have 24V on one side you should measure 0V across the coil!

 

[Eric Nelson]

If you measure 24V volts across the coil that means that the coil is "open".
When the coi is good and you have 24V on one side you should measure 0V across the coil!

Say what?!?! Perhaps you're thinking of fuses?...



-Eric

 

[rsdoran]

It would be difficult to make a relay activate without voltage present on the coil.

Across the coil means to test from the positive terminal to the common (negative) terminal, you MUST have voltage there of the coil can not activate. As was mentioned its current that "holds" the relay, it takes both for it to work.

The others have mentioned most of the reasons why relays dont always work. Relays have a "life span", if you make an effort to record when its put in and an approximation of how many times its cycled per day/shift, you can easily determine if its time to replace it even if it is not the immediate problem.

 

[TConnolly]

A voltage drop always exists across both a load and an open circuit, and a relay coil is a load. As Eric pointed out, perhaps you were thinking of a fuse, as no voltage drop exists across a good fuse as it is neither a load or an open circuit.

If you want to check for an open coil, simply unplug the relay and ohm the coil. You could also disconnect the neutral side of the relay coil and see if you read a voltage on that terminal when the relay should be on, if you do the coil is good. But thats more work than just unplugging the stupid thing and ohming the coil. When I buy ice-cube relays I always get the type with both a LED indicator and a mechanical indicator. Then you can see at a glance how the relay is functioning.

 

[rsdoran]

When I buy ice-cube relays I always get the type with both a LED indicator and a mechanical indicator. Then you can see at a glance how the relay is functioning.

Thats the kind to use these days BUT never forget that the relay may function but the contacts can be bad.

 

[elevmike]

All the indicator does is tell you if there's power on the coil terminals. The indicator could light, but the relay still might not be functioning.

If you measure 24V volts across the coil that means that the coil is "open".
When the coi is good and you have 24V on one side you should measure 0V across the coil!

NO!! If you measure 0v then there's no power beign applied to the coil, and the problem is somewhere else (not the the relay). What you need to do is unplug the relay and take a reading with an ohm meter accross the coil leads. If you measure 0 ohms then you have a bad coil.

 

[Unregistered]

Forgive me for being very crass , but I believe there is a base level of "knowledge" and below this , we should study a bit more before "hands on" .
like i said , I don't want to be hard , but this is a very simple problem , and OK if this is in a classroom , then there is no harm in "playing" , but if on a real machine where real fingers can get hurt , please learn a little more about basic electric circuits before going back to the machine.