Making sense of relays.

[Mike2007]

Hi,
I need to rewire this relay as it seems to be dropping out during service. Its a Rockwell 240v relay. How do I work out what each terminal does?
Its in the flue of a Stanley Range Cooker. Connected to cooker, exhaust fan and a pressure switch.

 

[EFLImpudence]

Is there not a diagram on the relay?

 

[ebee]

There is often a diagram on the relay and even if not you can usually determine which wire goes where so know the terminals by looking closely. I would start by suspecting the pressure switch operating correctly in the first instance before checking the relay though (unless you are confident that the relay is at fault).

Looks like a two pole change over relay at first glance and I cant quite see the number on it properly but if you can then you might google it for a diagram (or might not).

Some modern relays also have a mechanical test button on but I can`t see one in the pic.

 

[Deryck Tintagel]

As the others have said there is quite often a diagram on the relay itslef. Sometimes this is on the top or sometimes underneath by the pins. Can you rmove it from the relay base and have a look - you may find numbers against each pin. This is an octal base relay but yours may be different

 

[CBW]

I’d there’s no diagram on it, maybe it’s in the instructions for the cooker? If it’s a gas appliance the make sure you’re qualified to work on it if it’s classed as gas work.

 

[SUNRAY]

As the others have said there is quite often a diagram on the relay itslef. Sometimes this is on the top or sometimes underneath by the pins. Can you rmove it from the relay base and have a look - you may find numbers against each pin. This is an octal base relay but yours may be different


View attachment 338326

I doubt thats an octal relay,
First they are usually square
Second the base is invariably laid out like this

Third they invariably have the pinout in Deryck's post -- OP's unit doesn't have: pin 2 connected so no coil connexion or pin 1 connected so only one contact in use and pin 3 terminated but of no function.
Looking at the construction of the relay I feel this it the more likely format

such as https://www.cef.co.uk/catalogue/pro...-230v-ac-12a-miniature-plug-in-relay-with-led.
IF this is correct the relay effectively links the 2 reds together and the 2 yellows together which makes sense.

However if the relay is dropping out during use, I'd suspect a blockage in the pressure switch and its associated pipework, a blockage in the flue/clogged fan impellor or motor, a failed diaphragm or microswitch. These are not in any specific order as all of those are common issues.

Of course there could also be a problem with whatever is operating the fan.

 

[jj4091]

Has it been soldered into the base, normally they just pull out. Looks like one of these https://uk.rs-online.com/web/p/powe...IbW0-o06oI5yTpVn-oQaAvjPEALw_wcB&gclsrc=aw.ds Pull yours out of the base if it will, then check the base pins are the same orientation, remove the clear plastic cover and you may just find burnt contacts that you can clean with fine emery paper. Look at the technical details on the RS description and you should be able to work out how to make connections if necessary.

 

[Harry Bloomfield]

Looking at the construction of the relay I feel this it the more likely format

such as https://www.cef.co.uk/catalogue/pro...-230v-ac-12a-miniature-plug-in-relay-with-led.
IF this is correct the relay effectively links the 2 reds together and the 2 yellows together which makes sense.

The above is what I think I am seeing in the photos.

 

[SUNRAY]

The above is what I think I am seeing in the photos.

Not aimed specifically at you Harry but there are variations of the pin size and spacings so before ordering one pull it and make comparisons with on line images.
Example, these are both 12A:

but otherwise similar spec. The relay on the right will also fit in a 14pin socket so pin numbers are likely to either follow those already shown or be 1,5,9,13 down one side and 4,8,12,14 the other on this format

.

 

[FrodoOne]

Hi,
I need to rewire this relay as it seems to be dropping out during service. Its a Rockwell 240v relay. How do I work out what each terminal does?
Its in the flue of a Stanley Range Cooker. Connected to cooker, exhaust fan and a pressure switch.

While you wrote "rewire" it maybe that you mean "replace".
Since it is transparent, it can be seen that it is a DPDT (Double Pole Double Throw) relay - so it can be replaced with any 240 V DPDT relay (and Base) of - adequate switching (current) capacity.

On the existing Base,
Terminals 7 and 8 are for the Coil
Terminals 5 and 6 are for the Normally Open Contacts.
Terminals 3 and 4 are for the Commons.
Terminals 1 and 2 are for the Normally Closed contacts (and are not used.)

Edited/Corrected

(See https://cpc.farnell.com/c/electroni.../switches-relays-solenoids/relays/240v-relays )

 

[jj4091]

While you wrote "rewire" it maybe that you mean "replace".
Since it is transparent, it can be seen that it is a DPDT (Double Pole Double Throw) relay - so it can be replaced with any 240 V DPDT relay (and Base) of - adequate switching (current) capacity.

On the existing Base,
Terminals 1 and 2 are for the Coil
Terminals 3 and 4 are for the Normally Open Contacts.
Terminals 5 and 6 are for the Commons.
Terminals 7 and 8 are for the Normally Closed contacts (and are not used.)

(See https://cpc.farnell.com/c/electroni.../switches-relays-solenoids/relays/240v-relays )

I agree although 7 & 8 do appear to be in use. Unusual way of connecting a relay base though.

 

[ebee]

As I hinted at earlier,
it might be the relay that is not functioning correctly but it might be the sensor that is not switching properly (or it could be the connections).
If you have sufficient skill and knowledge to do it safely, then replacing the sensor with a link or a known good switch might lead you to determine whether its the relay (or base) that's the problem - 100 successful switch operations should give a strong indication say.
If all Ok then it looks like the sensor itself (pressure switch or whatever) and you could put a meter across it to test its resistance.
You could (do it safely though) waggle all of the connections to check for erratic switching, that should tell you that it`s the base itself or connecting wires that are the problem.

Or you could renew the relay, base, sensor and remake all the connections.

But do it all safely if you are handling mains connections. We generally accept that anything below 50v (in normal dry conditions only) as relatively safe, better still limit it to 12v or even 9v max (Do not put a 9v battery terminals across your tongue though - apparently millions do it every year but, apparently, that is not completely safe. Much in the same way you should not inhale laughing gas and speak "Duck", it`s a good party trick but can kill you!)

 

[ebee]

PS - what you have is a DPDT relay (2 gang 2 ways in effect), there is no harm in substituting for a 3 pole or 4 pole relay and in this application only needs Single Throw (1 way switching), so long as the relay coil is the same voltage rating and the contacts are rated at least for the current the existing one is and the sensor is rated for the coil current.

That opens up the choice of relays and bases if you know what you are doing.

 

[Harry Bloomfield]

That opens up the choice of relays and bases if you know what you are doing.

So far as I have read - We don't know what the 'sensor' actually is. In the past, I have designed circuits, where a sensor's resistance varies, and is carefully matched to the resistance, and sensitivity of the relay coil. I wonder if this might be so designed?

 

[ebee]

Good thinking there Harry, it might not be a simple on/off situation.

In fact if electronics is involved then it could even be akin to a 4 to 20mA loop or somesuch