How Does A Relay Work - SPDT DPDT SPST Automotive Relay

  • Published on Aug 16, 2015
  • You can buy various relays here:
    This video will explain how a relay works. I will show you different examples of various relays.
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Comments • 306

  • Aldiyar Kenes
    Aldiyar Kenes 7 days ago

    Love this video!

  • Sujith Dharmarajan
    Sujith Dharmarajan 10 days ago


  • lordoftheflings
    lordoftheflings 22 days ago

    wow fantastic explanation thanks!

  • Justin Gibson
    Justin Gibson 23 days ago

    Easy to understand with visual cues.

    SIMPLYBEAST1231 Month ago

    does SPTT exist?

  • Tony chatwin
    Tony chatwin Month ago

    Very helpful. Thank you

  • jeremy henderson
    jeremy henderson Month ago

    Hi, and thank you for your detailed explanation. (With a SPDT auto relay, JD2912-1Z-12VDC.) Does the coil and switch have to share the same power source (battery), or can they have different power sources?

    • jeremy henderson
      jeremy henderson Month ago

      That's what I believed when I bought them, but testing didn't reflect that. I must have had bad connection or something. :) That you.

    • dial2fast
      dial2fast  Month ago +1

      The coil and switch can use the same power source, or use different power source. The two are independent.

  • Iconic
    Iconic Month ago


  • Marcos Gomes
    Marcos Gomes Month ago

    This is a great explanation video, hard to imagine how it could be improved, maybe a couple of examples of basic circuits that use relays, but as for how they work this nails it.

  • Pimrawan Saikao
    Pimrawan Saikao Month ago

    You explain very good. I already subscribe your channel.

  • Derrick Desrochers
    Derrick Desrochers Month ago

    Dose it matter how 85 and 86 positive and negative is plug in

    • dial2fast
      dial2fast  Month ago

      It does not matter. It's just a coil inside.

  • 1 Author
    1 Author Month ago

    great explanation man! i understood in one go

  • Mthobisi Sibisi
    Mthobisi Sibisi Month ago

    Thank you so much you really helped me

  • Kabul Magak
    Kabul Magak Month ago

    Very good video

  • amiru asyraf
    amiru asyraf 2 months ago

    thank you

  • Matt R
    Matt R 2 months ago

    Great explanation... thank you!

  • Andrew Burn
    Andrew Burn 2 months ago

    Best relay video on TheXvid.

  • miharbi laucsap
    miharbi laucsap 2 months ago

    Hoping you make also for motor control pump combining with a diesel,jokey and induction motor pumps using this relays for connections.

  • elena olivares
    elena olivares 2 months ago

    You failed to mention the correct operation for each relay. Understand each relay has a specific job for a specific device. Also, you failed to mention how relays act when the points get carbon on them; if the points keep opening and closing if it is a head light relay the lights would continue to come on and go off even though the park lights would not come on unless the hazard switch on the dash is suppressed.
    So the point is the instruction is basic and not very professional/ complete. . . leaves the investigation in the dark.

    • dial2fast
      dial2fast  2 months ago

      Hence the title of this video is "How Does A Relay Work", and NOT How Does A Relay Fail. BTW park lights have nothing to do with hazard lights. Those are two different sets of lights on a vehicle with different circuits.

  • Allan Thomson
    Allan Thomson 3 months ago

    thank you - very
    understandable for novices

  • robert mccully
    robert mccully 3 months ago

    Automotive relays are typically rated at 30 or 40 amp? How do you know which one you have?

    • robert mccully
      robert mccully 3 months ago

      @dial2fast The values are not marked and its has a Ford Logo, made in canada. I have search the web and a lot of people are asking this same question. There are part numbers marked on them, but if i look them up there are no values.
      I guess the way to find out is to put a load on until it fries... You can buy millions of these at junk yards.

    • dial2fast
      dial2fast  3 months ago

      If it's made by a reputable company, it should be labeled with the rating.

  • Super Lit
    Super Lit 3 months ago

    you know what?
    This is fxxin' helpful at all.

  • kem mario Toredes
    kem mario Toredes 3 months ago

    Hi ser.. i want to know what is the difference then of using single throw and double throw..i mean what is their specific function and uses. And which is more efficient to chose between the two. Many Thanks

    • dial2fast
      dial2fast  3 months ago

      A SPST (single pole single throw), is just a single switch with two contact points that is on or off. A SPDT (single pole double throw), is single switch but with three contact points. One point will be normally open (n.o.), while the other will be normally closed (n.c.), and when you switch this relay, those two points will switch from n.c. to n.o, and n.o. to n.c. One is not more efficient than another. It just depends on what type of switching you need in your circuit.

  • Dylan Jones
    Dylan Jones 3 months ago

    So automotive relay coil is 2 powers or power and ground?

    • dial2fast
      dial2fast  3 months ago

      The coil has 2 connections. 1 is 12v, and the other is chassis ground.

  • Space Modafokka X
    Space Modafokka X 4 months ago +20

    I never like this thing when at school 2000, and 19yrs later this is what im looking for on TheXvid just for fun diy.

  • edbro Aotearoa
    edbro Aotearoa 4 months ago

    Very professional instruction. Thankyou

  • Ted Lahm
    Ted Lahm 4 months ago

    Wonderful. very clear.

  • Beshari Jamal
    Beshari Jamal 4 months ago +1

    cant be clearer, thanks for the video, going to the solid-state lesson now

  • conrad jr magdaong
    conrad jr magdaong 4 months ago

    thank you

  • Wang Hung
    Wang Hung 4 months ago

    are there relays that takes 12v trigger to energize but connects to 120vac line for devices?

    • dial2fast
      dial2fast  4 months ago

      Here is one:

  • Johnny Gallati
    Johnny Gallati 4 months ago


  • Carlos Delgado
    Carlos Delgado 4 months ago

    Best video ever!!! Thank you so much!!!

  • Shaikh Khalaf
    Shaikh Khalaf 5 months ago

    Thank you now professor we know very clear explanation Sir

  • Nicholas 1992
    Nicholas 1992 5 months ago +1

    Very well explained. Please if you can make the same video and well explained about contractors I would greatly appreciate it.

  • Muhammad Ezzatluqman
    Muhammad Ezzatluqman 5 months ago +2

    so helpful clear explanation thanks man!

  • tokunbo elufowoju
    tokunbo elufowoju 5 months ago

    Great video

  • human torch
    human torch 6 months ago +2

    Thank You Sir..Great Explanation!

  • james tomlin
    james tomlin 7 months ago

    i have a automotive relay, if take some batteries that equals 12v , will that make my relay click? 😀

  • Najd Al-Oqaili
    Najd Al-Oqaili 7 months ago

    I have one in PSU because of that i am here.

    TRICKSTA 7 months ago

    I finally get it.

  • H.R.I. services llc Ricky Hembel

    Excellent video, clear and concise! Thank you!

  • JS
    JS 8 months ago

    the best

  • Syazwan Rohaijat
    Syazwan Rohaijat 8 months ago

    For NTE transparent relay is for AC relay. But it have 28DC wrote there. Can i use 24VDC to energise the relay?

  • Fabio Copani
    Fabio Copani 8 months ago

    Awesome video

  • Helen Sosa
    Helen Sosa 9 months ago

    great video thanksssssss

  • riomar9
    riomar9 9 months ago

    dial2fast...GREAT VIDEO!!!
    I have a TPTT (TRIPLE POLE, TRIPLE THROW) RELAY - if that's what it's called since it has THREE separate contacts on EACH side, and not one or two (three NO, and three NC contacts, plus the 120 vac input side).
    Can the three separate relay contacts on either the NO or the NC sides be COMBINED AS A SINGLE CONTACT by joining the wires, to increase the Amp handling-rate on either the NO, or NC side?
    Relay info:
    120 V 50/60 HZ
    1/3 HP @ 120 VAC
    1/2 HP @ 250 VAC
    Below that it says:
    10 amps @ 250 VAC
    10 amps @ 28 VDC
    If I do that (combine the three on either NO or NC) would the TOTAL HP that can be used @ the 120 VAC - which is originally 1/3 HP - be up to 4 - 4.5 HP?...and:
    would the amp handling-rate also be raised to 30 amps or so…on whichever side I COMBINED? What say you my friend? Hope you understand what I'm asking?
    Thank you and best regards!!!

  • DrkBlueXG
    DrkBlueXG 9 months ago

    Wow good job

  • Bl1tzTurk
    Bl1tzTurk 9 months ago

    Let say you have 24DCV relay. You energize it and the contacts are closed. Doesnt this mean that there goes 24V trough to contacts? How you can measure these things?

    • Bl1tzTurk
      Bl1tzTurk 9 months ago +1

      @Babatunde Adepoju I already figured out by myself but still thank you for your explanation!

    • Babatunde Adepoju
      Babatunde Adepoju 9 months ago

      The currents passing through the coils to energize and what passes through the contacts are from two different sources. One power source energizes the coil to create the electromagnetism that pulls or closes the contacts, and another passes through the contacts when they are made.

  • Ztorm Sink
    Ztorm Sink 9 months ago

    Nice job. Now I get how it is working!!!

  • Ritvik Arya
    Ritvik Arya 10 months ago

    If i reverse the voltage on the coils of the relay, will the relay still work normally???

    • dial2fast
      dial2fast  10 months ago

      @Ritvik Arya You are probably referring to a flyback diode in parallel to the coil. If you are using this, then positive will connect to the cathode side of the diode.

    • Ritvik Arya
      Ritvik Arya 10 months ago

      @dial2fast What about the diode connected in parallel to the coil?

    • dial2fast
      dial2fast  10 months ago


  • Krissir
    Krissir 10 months ago

    Great explanation. I still am lost on why relays are used instead of just having a switch. I’m new to electrical so help me out please

    • dial2fast
      dial2fast  10 months ago

      A relay will allow a way to electronically control a switch. A circuit can energize a coil and open / close a switch. Whereas a switch is a manual way of turning on and off and requires a user to operate. You can also cascade a bunch of relays together in an automotive circuit to do all kinds of fun stuff, like reverse polarity door lock actuator to lock/ unlock car doors.

  • Aklilu Abraha
    Aklilu Abraha 10 months ago +2

    Great Video! Expecting More Like This! Thank you!

  • EvilJ069
    EvilJ069 10 months ago +1

    "Elektrizidy" lol

  • Em1
    Em1 10 months ago

    Yea 1 problem i have about that, there's no common in automotive if u can elaborate on thst good video

  • RainbowSixThree Enlightened
    RainbowSixThree Enlightened 10 months ago +5

    If you put your left finger on one pole, and your right finger on the other pole, and then place a popcorn kernel in your mouth and then turn the switch on, will you spit it out?

  • Matt Bruce
    Matt Bruce 10 months ago

    Great video and very well explained. Thank You!

  • Christopher Lindgren
    Christopher Lindgren 10 months ago

    The DC .coil any difference in +, -?

    • dial2fast
      dial2fast  10 months ago +2

      No, it's not polarity sensitive.

  • Joshua Gbuah
    Joshua Gbuah 10 months ago

    Very clear explanation. I am interested in Power System Control and Protection and will like to have a broader understanding on relays. Do you offer training for that as well?

  • BadRonald1
    BadRonald1 11 months ago

    Ok got it.... But how am I going to know which type of relay I need ? If I want to install 2 12v headlights to the front of my car, do I need a SPST relay or a SPDT relay ?

    • Fu Sensei
      Fu Sensei 11 months ago +2

      2 pcs SPST, 1 for each side , 30+Batt 85+trigger 86-ground 87+headlights

  • Brian Malonzo
    Brian Malonzo Year ago

    Thank You.