electrical relays

[Gregster613]

I've got a question about relays; I searched but couldn't seem to find my answer. I'm not the sharpest tack in the box with electrical stuff so thought I'd ask. I bought a supposed relay tester to simply check if a relay was bad or not but it didn't seem to work so I threw it away. It would spark when hooking to the battery posts. Yes I hooked red to pos and black to neg.

Thinking about it later, I wondered if it was just that I had the wrong type of relay I was testing. My suspect relay has 3 pins on the end - my tester was supposed to be able to check 4 or 5 pin relays. Does a normal relay have 4 or 5 pins? Would a 3 pin relay be the same as a 4 pin? That's what I had my tester set for but because of the sparking issue I didn't want to trust it or even continue messing with hooking it to any battery. Could have simply been faulty out of the box. Bought from Amazon vendor and was pretty cheap.

Should I search for a replacement tester? Does it have to specify 3 pin ability? I like the idea of testing a relay prior to just buying one and you-tube videos show it as being a simple hook up and hearing the click as relay opens or closes. There were no sparks on the videos though. I'd think most relays would be close to the same but I'm just not sure. A dummy asking for advice.
Thanks, Greg

 

[k0ua]

I have never seen nor heard of a three pin relay. I am trying hard to envision such a thing, but I cannot. But I do learn new things every day. But I cannot envision how a 3 pin relay would work.

Imagine this: a relay normally has a coil, this coil can be set up for AC or DC. DC coils sometimes have a diode across the coil. The DC relays need to maintain polarity if the diode is present. The diode acts as a "snubber" to short out the reverse pulse coming out of the coil when the power is removed. Now on to the other terminals. When the coil is energized, you have a movable "armature" or contact that moves. The armature contact moves to make contact with one of the other terminals. This other contact is NO or "Normally open" This is a 4 terminal relay. A 5 terminal relay has the armature contact already making contact with the NC or "Normally Closed" contact by spring pressure. This is in the NON energized state that it is making this contact. When energized it moves over to make contact with the NO "Normally Open" contact just like the 4 pin relay and of course its contact with the NC contact then opens up.

I have never needed a relay tester. I just use an Ohm meter, which I have many of anyway for a thousand other tests. I can go into that if you like on another post.

The 30,000 foot picture I think you need to understand is what does a relay do? What is the purpose of these things?
A relay us usually used for one of two reasons, or both of these reasons.

Reason one is to have the relay contacts switch a load that is high current and allow it to be controlled by a tiny low current switch.

Reason two is similar but slightly different in that you are controlling a high current load at a distance. Example to avoid voltage drop in having a high current switch switching a high current load but the switch is located some distance from the load, you suffer the losses in the voltage drop even though the switch is capable of switching the load.

Here is a real world example. You have a high current load of a light bar on your auto out front on the bumper.
But you have to control those lights on the dash of your auto. You want to use a tiny switch and tiny wire run to your dash to control the relay coil. The relay coils requires very low current to energies the coil. The contacts to turn on those lights are made to handle high currents and the wire feeding the armature contact and going out to the lights on the NO contact are heavy gauged wire up front with the wiring being short in length coming from the battery and going out to the lights.

This concept minimizes voltage drop, and allows a small switch in the dash to control a much larger current out front. Also the wire going out front could likely be just a single small guage wire as you can pick up a voltage up under the dash from some other circuit and send that to the relay coil. Ground can be picked up locally at the relay.

Hmmmmm. 3 pin relay. MAYBE, there could be a "3 pin relay", that is NOT really a 3 pin relay but is in actuality a 4 pin relay, because the mounting tab of the relay is the negative or ground side of the relay coil, then one of the other pins could be the positive of the coil. Then the remaining two pins could be the armature (movable contact to battery) and the other pin could go to the load.

How about that for an idea?

 

[Richard001]

Gregster,
You don't specify, but I assume that you are talking about typical automotive 12V DC relay.

If you could post a photo of the relay in question and also explain what you intend to use it for, that would clear up a lot of questions.

 

[K5lwq]

Timer relay may only need 3 wires. One wire is the signal to the relay while the other two carry the load. Other than that I can not think of a 3 prong relay.

 

[i7win7]

All relays have a power terminal and a load terminal. if the 3rd terminal has power (hot) then it has to be grounded to work. Personally I'd use a 4 or 5 terminal relay

 

[WranglerX]

Never heard of a 3 pin relay .... Only 3 terminal device I can think of is a turn signal flasher (possible referred to as a "relay") .... All relays I have ever been associates were (minimum) 4 pin, two pins for coil to operate relay, 2 pins for contacts in relay.... The there 5 pin relays with have a normally open and normally closed contacts or normally open relay with two common out put contacts contacts.

Enlightenment is just below....

Understanding Relays & Wiring Diagrams | Swe-Check

A relay is an electrically operated switch. Learn how to wire a 4 or 5 pin relay with our wiring diagrams and understand how relays work.

www.swe-check.com.au

How Relays Work

FREE COURSE!! Learn the basics of relays to understand the main parts, the different types as well as how they work along with worked examples.

theengineeringmindset.com

 

[hosspuller]

OP's "relay" may not be a conventional solenoid coil relay. It could be a transistor, SCR, Triac, or other semiconductor device.

Gregster... Post a photo of the "relay". And where it's used.

 

[Richard001]

Hey here is a three terminal relay:

 

[DonRybak]

This seems silly to me. You close the switch to energize the coil and closes the contact which then supplies voltage to the load. Why not just have the switch in place the the relay contact? Hmmmmm, I'm sure there must be a reason but it escapes me at this time.

 

[jaxs]

Having tested thousands of relays spanning several decades I can tell you with confidence there is no such thing as a "relay tester"and anyone marketing one is a con artist. Forgive me for saying so but your question(s) sound like bait for another endless thread.