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5 Pin relay

GatorGnet

New Member
I'm really showing my newb tonight. I have picked up some 5 pin relays and cant find a datasheet for them. I need to know how to hook these up on one of our pcbs. As far as I can see, pins 2 and 5 are the coil but what about 1, 3, and 4? How would this work? FYI its a SPDT relay.

 
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GatorGnet

New Member
I'll take a shot and see if I'm right. 2-GND, 5-+(in this case its 6v), 1-Source(eg 110v ac), 3- output of 1 NO and 4- output of 1 NC?
 

vne147

Member
I'm really showing my newb tonight. I have picked up some 5 pin relays and cant find a datasheet for them. I need to know how to hook these up on one of our pcbs. As far as I can see, pins 2 and 5 are the coil but what about 1, 3, and 4? How would this work? FYI its a SPDT relay.

As you've stated pins 2 and 5 seem to go to the coil. Pin 1 is the common pin. Pin 4 is the NC (normally closed) pin and pin 3 is the NO (normally open) pin.

When the relay is not energized, there should be continuity between pins 1 and 4. When the relay is energized, there should be continuity between pins 1 and 3. Apply a low voltage across pins 2 and 5. The lower the better until you are sure what voltage the relay can take. I'd say between 3V and 5V would be fine. If when you apply this voltage you get continuity between pins 1 & 3, then you have just made the relay change states. You will probably also hear an audible click. If you don't get continuity between pins 1 & 3, reverse the polarity of the voltage you are applying across pins 2 and 5 and try again.

EDIT: Sorry forgot to add, if you try both polarities and you still don't get continuity between COM and NO, up the voltage a little and start the process over again.
 
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Hero999

Banned
Here's a schematic. The switch position is shown as is with no power applied to the coil. When the coil is energised the common (the unlabled pin at the top) is linked to the NO (normally open) connection.


 

GatorGnet

New Member
Does it usually matter which way the voltage is applied to the coil? I will try it out when they arrive but I am trying to finish the pcb.
 

vne147

Member
Does it usually matter which way the voltage is applied to the coil? I will try it out when they arrive but I am trying to finish the pcb.
Yes, it matters. If you apply voltage of opposite polarity than the relay was designed for, then the wiper of the relay will be forced against the NC contact. That's why I said try it one way and if you don't get continuity between COM on NO, switch the polarity of the applied voltage and try again. I didn't realize you were still waiting for these relays to arrive. When you get them, the polarity and coil voltage might be printed on the top. Let me know how it turns out.
 
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Nigel Goodwin

Super Moderator
Most Helpful Member
Yes, it matters. If you apply voltage of opposite polarity than the relay was designed for, then the wiper of the relay will be forced against the NC contact.
Sorry, but that's completely wrong - it makes no difference which way you wire the coil - it's pulling on a piece of plain steel, so polarity doesn't matter at all.
 

GatorGnet

New Member
I forgot to ask but should I place a diode between the coil and the transistor? If so, which is better, between the positive or ground?
 

vne147

Member
Sorry, but that's completely wrong - it makes no difference which way you wire the coil - it's pulling on a piece of plain steel, so polarity doesn't matter at all.
I don't know if that is because of the specific type of relay he has pictured there but I've played with open relays before where that's exactly how they worked. If I applied voltage one way I could see the little spring arm on the contactor getting bent because it was being pushed against the NC contact. If I reversed the polarity of the voltage I was applying to the coil, the contactor moved over to the NO contact. Why did that happen?
 

Nigel Goodwin

Super Moderator
Most Helpful Member
I don't know if that is because of the specific type of relay he has pictured there but I've played with open relays before where that's exactly how they worked. If I applied voltage one way I could see the little spring arm on the contactor getting bent because it was being pushed against the NC contact. If I reversed the polarity of the voltage I was applying to the coil, the contactor moved over to the NO contact. Why did that happen?
It would happen if the arm contains a magnet, or was magnetised - however, I've never seen a relay that does (do latching relays perhaps?). If any such relay did, then the coil pins would be clearly marked with their polarity.
 

GatorGnet

New Member
The coil voltage for these are 6v and as of now, the two voltages I have on this pcb is 12 and 5. Could I just use a resistor form the 12v supply and power it with that?
 

vne147

Member
It would happen if the arm contains a magnet, or was magnetised - however, I've never seen a relay that does (do latching relays perhaps?). If any such relay did, then the coil pins would be clearly marked with their polarity.
Nigel,

I was so convinced that I was right that I ran into my workshop and grabbed one of the relays I referred to in my last post. I hooked everything up and tested it out and I can now officialy report, I'm totally wrong. The polarity of the voltage applied to the coil doesn't matter (at least in the case of a non-latching relay).

However, I'm certain I wasn't hallucinating when I saw the relay act the way I described. I'm going to just chalk it up to a faulty relay or perhaps something wonky in my test circuit. At any rate those two possibilities seem more likely than the laws of physics temporarily being suspended in the space above my work bench.

Thanks for the correction to my post and to my understanding.


Gator,

Sorry for the bad info. However, the procedure I outlined for you my first reply is still valid. You just would have taken a few extra unecessary steps. First off, when you get the relay if there is anytihng printed on the top, use that over the test procedure. If there isn't anything on top, just start by applying a low voltage to the coil and increase it gradually until you get continuity beteween COM and NO.
 

vne147

Member
The coil voltage for these are 6v and as of now, the two voltages I have on this pcb is 12 and 5. Could I just use a resistor form the 12v supply and power it with that?
Once you get the relay, measure the resistance of the coil. If you place a resistor in series with the coil that has equal resistance as the coil and apply 12V that should cause the voltage drop over the coil to be 6V. At least there is no reason I can think of why that wouldn't work but if not it wouldn't be the first time today that something I thought I knew turned out to be totally wrong. :D
 

Hero999

Banned
It depends on the relay for a simple SPDT relay it doesn't matter.

I know that there are latching relays which have a permanent magnet so if power is applied in one direction, the relay turns on, if it's applied in the other direction, it turns off.

It wouldn't surprise me if you can buy a SPDT relay which has neither contact connected when no power is applied to the coil and a different contact is connected depending on the direction of the current applied to the coil.
 

vne147

Member
It depends on the relay for a simple SPDT relay it doesn't matter.

I know that there are latching relays which have a permanent magnet so if power is applied in one direction, the relay turns on, if it's applied in the other direction, it turns off.

It wouldn't surprise me if you can buy a SPDT relay which has neither contact connected when no power is applied to the coil and a different contact is connected depending on the direction of the current applied to the coil.
Good info Hero. Thanks. There is still a shred of hope then that I'm not crazy. Just a shred though.
 

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