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Replace Relay with TRIAC?

Discussion in 'General Electronics Discussion' started by CMA, May 15, 2017.

  1. CMA

    CMA

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    May 12, 2017
    Is it possible to replace the relay with TRIAC for more reliability and silent? Or is there better electronic that can simply turn off and on?

    For example... my car has relay so can TRIAC replaces it?

    [​IMG]

    Thanks again!


    PS. I am not genius but will learn a bit.
     
  2. 73's de Edd

    73's de Edd

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    Aug 21, 2015
    Sir CMA . . . . .

    Considering the infrequent switching needs . . . . ON when the car is running and OFF when the car is not being used.

    Along with:

    • The milliohms of contact resistance of a mechanical relays contacts.
    • Not having to worry about the “ trash “ being fed into the gate of a TRIAC.
    • The extremes of the environmental swings under the hood, that this would be subjected to.
    I will still take the car manufacturers selection of a type approved auto relay that has been subjected to exhaustive testing and probably prior experience of the unit having proven its reliability, in prior same applications by that car manufacturer.

    If this relay application actually involved actual repetitive switching on and off functions . . .tens . . . hundreds . . . thousands of times, that TRIAC utilization might then start to shine.


    73’s de Edd
     
  3. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Besides, the important points that Ed gave you there must be a means of turning a Triac or SCR off. They don't turn off when gate current (your Gate switch) is cut off.

    Chris
     
  4. Audioguru

    Audioguru

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    Sep 24, 2016
    Triacs are used in AC light dimmers. Mosfets are used as DC switches in modern cars. Relays were used in old cars.
     
  5. CMA

    CMA

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    May 12, 2017
    Hmmm

    - What do you mean trashed feeding into TRIAC?
    - The fusebox and relay is in the cabin...

    That's interesting... that's for AC... so it's not for DC? and is there another kind of MOSFET that turns on and off like you said?

    Maybe I can use MOSFET then? I am trying to replace relay for 1 less wire + lightweight.

    btw I use this sources

    http://www.signindustry.com/electric/articles/2000-11_ALDORtriacexplainted.php3
    http://electronicsbyexamples.blogspot.ca/2013/06/switching-ac-loads-with-triac.html



    Thanks.
     
  6. Audioguru

    Audioguru

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    Sep 24, 2016
    A triac is usually used with AC but will work with DC (but then half of it is not used). An SCR is the half of a triac that can be used with DC.
    A Mosfet is a powerful transistor used with DC.
     
  7. duke37

    duke37

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    Jan 9, 2011
    I car has an electrial system with large currents and long inductive wires. Any disturbance to the steady state will generate voltages in all sorts of places. This is colloquialy called trash. A MOSFET is very sensitive to voltages at the gate so funny things can happen unless this trash is kept under control.
     
  8. BobK

    BobK

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    More often called "noise."

    Bob
     
    Harald Kapp likes this.
  9. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Actually if we want to get really picky regarding proper (technical!) terminology I can't help but remembering my first job after mustering out of the Army. I worked under (Bob) a crusty old Signal Corps tech. The company had a contract refurbishing ARC34 aircraft Tranceivers. These things were powered by a Dynamotor that was eventually replaced with a electro- mechanical Multivibrator. Then later replaced with a solid state version. I guess one could equate them to a funky SMPS.

    One day while I struggled to get one of these beast to meet transmitting and receiving specs when Bob rolled a Techtronics over to my bench. Within a few minutes he bellowed ..... "Well there's your problem boy! Look at all that Sh!t floating around on your B+!"

    So now you know one of the more accepted 'Technical' terms for electrical noise. :D

    Cheers!
    Chris
     
    73's de Edd likes this.
  10. BobK

    BobK

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    Chris,

    Yes, "shit" is the mil-spec term.

    bob
     
  11. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Bob,

    You got me thinking that there should be a military acronym in there somewhere. The military loves them you know. Problem is I can't get past "Spurious" for "S".

    Chris
     
  12. CMA

    CMA

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    May 12, 2017
    Alright... that's interesting to read!

    SO trashed feeding = dirty or noise electricity... could be solved by
    > capacitor (conductor)
    > shield ground wire
    > diode

    no?

    I still would like to use MOFSET for efficient so I am still curious what kind of MOFSET that is... as long as I could research how to make sure that the voltage is not too sensitive. I just like to use "gate" as voltage input as switched on.

    CDdriver... That's very interesting... that crazy dynamotor is freaking big and heavy! And what kind of solid state? does it replace with? solid state relay?

    Thanks.
     
  13. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Yes, Dynamotors were big, heavy and (P-in/P-out) inefficient. They were also durable and very tough to kill! They could survive severe overloads and keep on purring. This photo is what I believe to be (haven't seen one since 1967) the transistorized Multivibrator replacement. The Dynamotor and the MV version plugged into the main unit and held fast with sliding latches.

    upload_2017-5-16_10-34-11.jpeg

    Transistors at that time line were Germanium junction. Few of us (not even the senior techs) had much experience with them. It was a Vacuum Tube world back then. How the hell these things ever passed MIL SPEC eludes me. Durability was not the benchmark of Germanium junctions. They'd blow their brains out with the briefest overload!

    To answer this question:
    The primary windings of a Step - Up Transformer formed part of the multivibrator circuit. The Secondary of the Transformer produced HV AC and was rectified and filtered.

    Now that that little bit of history is out of the way let's get back to your topic.

    As I stated earlier TRIAC's & SCR's (Thyristors) don't turn off merely because the gate signal has been shut off. An SCR (in your case) will require either of 3 things to occur. Anode to Cathode current is either cut off, bypassed or the polarity is reversed. Oh, there's one more thing that will shut it off. That would be that the Anode - Cathode current has fallen below the SCR's "Holding Current" rating. This value varies depending upon the model.

    If I were you I'd forget using an SCR. For that matter I still reiterate ALL the relay benefits that Ed so clearly pointed out.

    Chris
     
  14. CMA

    CMA

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    May 12, 2017
    Alright thanks for history.. it was interesting to see how it evolved.

    I will take your advice to keep the relay and its extra wire. Hopefully I can find a lightweight EM relay.

    Thank you all for information.
     
  15. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    I don't think it would be fair to your interest in electronics to let you leave this topic without giving you something related to solid state switching. This is the basic circuit configuration used for High Side solid state switching.

    When S1 is open Q1 is off. This in turn holds Q2 (P Chan MOSFET) also OFF. When S1 is closed Q1's Base - Emitter junction is forward biased. This turns the Collector-Emitter junction on. This pulls the Gate of Q2 to near Ground (-) potential with respect to the Source terminal that's connected to +12V. This in turn turns Q2 ON where output is taken off the Drain.

    Note: No protection has been included to protect the circuit from Bob's ... uh ..."MIL SPEC"! :)

    Cheers,
    Chris
    upload_2017-5-18_11-18-38.png
     
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  16. CMA

    CMA

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    May 12, 2017
    okay I see
    - 2 power sources
    - 1 switch
    - 3 resistors
    - 1 Transistor
    - 1 MOSFET.
    - 1 Load

    That's more complex that I expect...

    Therefore the relay would better application for my car.

    Thanks for explaining the example.
     
  17. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    There's only one power source. That's the car's battery. The load isn't a component of the circuit itself. It represents whatever your relay was powering in your circuit. If this circuit was replacing your relay then the switch in my circuit would be the switch in your circuit too.

    All that said, please stick with the relay. It doesn't give a Rats A$$ about electrical noise.

    Chris
     
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  18. CMA

    CMA

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    May 12, 2017
    I thought vout is misspell as volt therefore two power sources... vout = ? other word for voltmeter?

    Well I still want to avoid electronic noise because it wastes watts. I tried to make my project to be 99%+ efficient....

    Of course I will use the relay with diode in the future...
     
  19. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    By your last reply I'm beginning to think that your first post (automobile schematic included) has nothing to do with what your project is. Care to elaborate?

    Chris
     
  20. CMA

    CMA

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    May 12, 2017
    Hmm. Not sure what you meant?

    That diagram I posted is actually from the factory service manual which has relay for EFI system. I was asking if I can replace the relay with anything. The car only have 4 relays for EFI, FP, Radiator and Horn.

    My goal is improving the harness as high efficiency harness since the factory harness is about 27 years old.
     
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