Difference between 4 pin and 5 pin relays?

[Jon K]

I have a bunch of "30A Automotive Relays" I bought a long time ago to do some wiring for my stereo - by a bunch I mean like 30 of them. While messing around with my ECU install and what not I notice the Main relay on my 1992 525i is a 4 pin I believe, while the oxygen sensor relay is 5 pin... whats the difference?

[winfred]

not all 4 and or 5 pin relays are the same, the pin positions change and theres a few options on what they do, the standard 4 pin is 86/85 to energize the coil 30 power in and 87 power out, on 5 pins the center can do many things like a secondary 87, a alternitive 87, a alternitive 86 and a few other combos

[joshua43214]

The 5th pin is often a signal wire. It will have an "a" suffix on the pin that is a signal, such as an 87a pin that will turn on an indicator light to let you know that something is turned on. If it follows the din "norm", it will be the center pin, but as Winfred stated, even 4 pin relays are not all the same, and 5 pin relays tend to have even more variation.

[PaulJ]

Depending on the pin nomenclature of course, usually a 4 pin relay has 2 pins for the coil and 2 pins for a single contact either normally open (NO & C)or normally closed (NC & C). The 5 pin relay will also have 2 pins for the coil and could have both a normally closed (NC) and a normally open (NO) contact with a (C) common pin switched between them. If the pins aren't identified, use an ohmmeter to identify the coil terminals and apply the appropriate voltage to operate the relay. Use the ohmmeter to identify the contact arrangement.

Paul

[zygoteer]

this picture may help ....

[Jon K]

Can you explain the key? Colors and symbols?

[zygoteer]

this picture may help ....

A relay is an electrically operated switch, and its the operating circuit (the coil - usually depicted by a rectangle with a diagonal) has ID '86' for positive (12volt nom. - input); and ID '85' for negative (vehicle ground - output).
Most relays are not polarity sensitive, but a few diode protected or latching types are, so always use '86' as the positive side to be safe.
The circuit the relay is to switch has ID '30' for the positive input contact of the circuit, and either ID '87' or '87a' or '87b' for the negative output contact of the circuit.
Note : the input is not necessarily 12volt and the output is not necessarily vehicle ground, as some schematic designs switch the 'high side' or positive side of a device, and some switch the 'low-side' or negative side of a device, so check your circuit schematic.


Relay contact layouts come in various forms and the picture shows the commonly used automotive ones, which are mostly single pole types (there are theoretically hundreds of different layouts, but don't worry about them as they are rare and are essentially just variations in number of poles and active contacts).
The common contact layout types are referred to in much the same way as mechanical switches, and are :
NO = 'normally open' circuit, when no voltage is applied to the coil., sometimes described as 'single pole/single throw/make' or 'SPST-make' or 'SPST-NO'
NC = 'normally closed' circuit, when no voltage is applied to the coil, sometimes described as 'single pole/single throw/break' or 'SPST-break' or 'SPST-NC'
... single pole here means a single switched circuit.
... single throw here means a single contact is 'made' or 'broken'.
These are the '4-blade' relay types.


Sometimes a relay will have a 2nd switched output contact - this is the '5-blade' relay type.
The three common ones are shown in the picture.

On the left we have a output contact that has both 'NC' and 'NO' output contacts, so the relay action is to change the circuit from :
'30' connected to '87A' when no voltage is applied to the coil, to :
'30' connected to '87' when voltage is applied to the coil.
This is often called a 'change-over' switching action or 'CO' or specifically 'SPCO'.

In the middle we have two 'NO' output contacts, so the relay action is :
'30' NOT connected anything when no voltage is applied to the coil, to :
'30' connected to both '87' and '87B' when no voltage is applied to the coil.
This is called a 'single pole/double throw/make' or 'SPDT-make' or 'SPDT-NO'.
(it has to be said that some people call this a 'SP3T', as 3 independant contacts are connected when energized)
The advantage of this is that until the relay is energized, the '87' and '87B' circuits are NOT connected to each other.

On the right we have a '5-blade' version of the '4-Blade' version described above as 'SPST-NO' ... it is simply a convenient way to provide an extra physical blade connection on the output, so both blades have the '87' ID.


Very occasionally you may find some double pole relay types, but they follow the same principles as above and of course will have more blade connections, so the physical package will be very different and probably specific to a manufacturer = probably expensive!

... ok looking back at this, it seems I have made it look complicated - sorry.

[JMI]

this picture may help ....

What is the source of the picture. Looks like a book/manual worth purchasing.

Thanks

Jim

[Jon K]

Thanks Zygoteer - let me ask a cheater question. I did read your post... but...

Why would the main relay have a 5 pin relay?

More importantly, I want to make a relay that supplies 12v to an object when the ignition is switched on. I know where to find the ignition wire, I know where to find ground points, and I have a couple +12v constant sources in there, so how would I set up a relay and would it be a 4 pin or 5?

[winfred]

the main on most bmws has 2 87s to power more then one circuit. to wire a 4 pin simple relay hook the 30 to the battery, through a fuse if you want the circuit protected, 87 goes to what you want to power up and how you switch it depends on how you want to wire the system, to turn on the relay you need to get ground and power to 85 and 86 (doesn't really matter which gets - or +) you can jumper power from 30 to 86 and actuate the circuit with a ground to 85 or run 86 directly to ground and run a power to 85 to actuate the circuit. 4 or 5 pin depends on if you want any options, like a 2nd 87, a 87a that's powered up with the relay open (powers off when you turn on the relay) a indicator light or whatever

Thanks Zygoteer - let me ask a cheater question. I did read your post... but...

Why would the main relay have a 5 pin relay?

More importantly, I want to make a relay that supplies 12v to an object when the ignition is switched on. I know where to find the ignition wire, I know where to find ground points, and I have a couple +12v constant sources in there, so how would I set up a relay and would it be a 4 pin or 5?