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New components tests, vs Old components tests

Discussion in 'General Electronics Discussion' started by tedstruk, Nov 11, 2018.

  1. tedstruk

    tedstruk

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    Jan 7, 2012
    I am boggling again...
    Assume you have to replace a triac and order a new one. It arrives and you install it. Fine everything works.. but later you test the spare you got, and it tests bad?
    Well I am thinking, and triac doping is kinda power sensitive....
    Would a trlac that has never had any signal through it, test weird?
    I am saying it's poll time!
    And I am thinking that this could be happening ....
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    How did you test the triac to assure it's bad? The failure could be with your test, not the triac.

    There's always a risk that a component fails DOA or due to improper handling.
     
  3. kellys_eye

    kellys_eye

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    ISTR that the OP uses one of those Chinese component testers - I know from experience that they tend to show triacs as a low-ohm resistor whether or not they are good/bad. Those testers are not suited to this type of component.
     
  4. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    ISTR = It stands to reason?
     
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  5. kellys_eye

    kellys_eye

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    ISTR = I seem to recall

    standard internet shorthand.
     
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  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    "Standard" and "internet" used in the same sentence -- ROTFLASTC!

    Yes, where they are able to test SCRs and TRIACs, they are frequently only able to maintain a current too low to hold device on.

    Since @tedstruk has refused to answer all questions about how he tests the devices, we can't really help him.
     
    Harald Kapp and davenn like this.
  7. kellys_eye

    kellys_eye

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    I wondered if anyone would catch that! Well spotted :p
     
  8. tedstruk

    tedstruk

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    Jan 7, 2012
  9. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    As we suspected. You should not be surprised that this can't test many SCRs
     
  10. bushtech

    bushtech

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    From your tester's sales blurb:

    1.28 Thyristors and Triacs can only be detected, if the test current is above the holding current. Some Thyristors and Tnacs need as higher gate trigger current,

    than this Tester can deliver The available testing current is only about 6mA.
     
  11. kellys_eye

    kellys_eye

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    Yep, as expected, cheap Chinese tester. Although that particular tester is very good (in MOST applications) it's not perfect for ALL devices so you have to live with its limitations.

    If you want to test such components in greater detail/accuracy you need something like this:

    https://www.peakelec.co.uk/acatalog/scr100-triac-scr-analyser.html
     
  12. tedstruk

    tedstruk

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    Jan 7, 2012
    https://www.electronics-tutorials.ws/power/triac.html
    So by the schematics I found here, IF I had to, I could build one using diodes in a similar configuration, so as the diodes were the right avalanche voltage?
    'I am considering using the triacs I bought on ebay...which didn't test as thyristors or triacs but as 2 resistors, just because me meter is cheap.' I am very worried about you guys... you should think about seeing somone about that...

    I got some 3A 250v fuses for sale if anyone needs them.
     
  13. kellys_eye

    kellys_eye

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    A triac is (basically) two thyristors mounted back-to-back.

    A thyristor only conducts over one half cycle of an AC waveform whereas the triac conducts over both cycles (positive and negative).

    There is a procedure for testing such components and if your test meter doesn't follow this procedure then it doesn't necessarily mean the device is faulty - it means it can't be properly tested.

    Connect your thyristors/triacs to a low voltage AC source and PLAY WITH IT....... use different value resistors to trigger them etc and see for yourself what is required to make them do what they are meant to do.
     
  14. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    They're not diodes.

    That comment reads as an insult coming from someone who knows little and directed toward those who seek to help you. I would be very careful about buying the hand that feeds you.
     
  15. tedstruk

    tedstruk

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    Jan 7, 2012
    I have been waiting for thyristors from china for 32 days.
    They have changed the delivery date 3 times from Dec 7 to Dec 14 to Dec 19...
    I went to Jameco and ordered some SCRs of the right type that are from the West coast and should be here in a few days... Tuesday or Wednesday anyway.

    I think half my problem is waiting. My paycheck is always late when I can really use the pay.
     
  16. kellys_eye

    kellys_eye

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    Not a good place to purchase parts if you intend using them anywhere near their rated maximum. The incident of 'fakery' when it comes to specifications of such devices is quite high - anecdotally.

    Getting the parts from a reputable supplier (Jameco for example) is far better - you will, at least, have someone to complain to if the parts turn out to be fakes......!
     
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