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  • Need Part Number

    I'm in need of the part # for the varistor on the bottom of the mp chassis for the table contactor. Any help would be appreciated.
    Thanks

  • #2
    Re: Need Part Number

    Nick, just forget about it. The chassis will run fine w/o it & basically you are better off w/o the darn thing. If you really want to put the thing in, just let me know & I'll send you one gratus. Personally, I'd cut all of them out. I have yet to see a relay or contactor fried because the varistor isn't there. They cause more problems then they prevent IMHO.
    I've had enough of hope & chains.

    Comment


    • #3
      Re: Need Part Number

      Well, if you want the number anyway, it's 748 010 034.

      Comment


      • #4
        Re: Need Part Number

        Originally posted by wb8yjf:
        ... I have yet to see a relay or contactor fried because the varistor isn't there.
        <font size="2" face="Verdana, Helvetica, sans-serif">That's because they don't protect the contactors or relays.

        They protect the control board outputs against transients created by the contactors and relays.

        The outputs protected are: table, sweep and spot relay. If these outputs get zapped (by not having a varistor), you'd either get no run or continuous run.

        The M relay also has one, but I'm not sure why (doesn't seem to protect anything except the LIU, which should have its own protection).

        The important question is: when a varistor fails, would the board have been damaged had the varistor not been there?

        If the answer is yes, then clearly the varistor is an important element, since board repairs are more costly than varistor replacement.

        However, varistors tend to break down over time, even when the transient voltage is not enough to damage the protected device (the board). It may absorb hundreds or thousands of transients before failing. If any one of those transients are enough to damage the board, then the varistor is necessary. But if none of the transients would have damaged the board, then the varistor is not serving a purpose.

        It's a difficult question to answer because the board output devices usually have some in-built protection, and the extent of transients is difficult to predict.

        But the failure rate of varistors (on boards with a full compliment) can be compared to the failure rate of the protected inputs on boards with no varistor protection (as long as you compare boards with the same output devices).

        From that you could infer the value of the varistor protection in this application.

        Cheers,
        Andrew.

        Comment


        • #5
          Re: Need Part Number

          can you put that into english please!!!!!
          Regards,

          Len.

          Comment


          • #6
            Re: Need Part Number

            Andrew,
            I tend to agree with you in that regard, but I still have a problem with varistors in this application. Basically these varistors are across the outputs of the triacs &amp; consequently the coils of the contactors &amp; the M relay. I have seen many boards that have had the traics zapped, and many that have had the varistor zapped too. On chassis that I have eliminated the varistors, I haven't seen any increase of traic failure. I understand why they are there, but it seems to make virtually no difference if they are there or not (IMHO). The kick back from the coil is somewhat suppressed from the capacitors in the driver circuit, which seems to take care of this most of the time. With any relay or contactor coil in a circuit, you always have the possibilty of a large surge which could zap a triac, but I haven't seen much of this. I agree they are there for a reason, but when they fail, they tend to drive mechanics nuts! [img]/content/btubb/images/%%GRAEMLIN_URL%%/eek.gif[/img] Both have a tendency to fail over time. Not to mention other factors...ie: pulling a board with the power on...I'm just saying, you don't necessarily have to have them, they may provide some protection, but they are a pain when they fail. I still have yet to find an effective test to check the status of a varistor other than shorted or not shorted. If there is an effective "condition" test, PLEASE let me know! [img]/content/btubb/images/%%GRAEMLIN_URL%%/laugh.gif[/img]

            All I was saying is you don't have to have them to make a chassis run. :p and a lot of times, they make troubleshooting for a center mechanic a lot harder and frustrating.

            JMHO... [img]/content/btubb/images/%%GRAEMLIN_URL%%/143.gif[/img]
            Jon


            Len: that is in English! :p
            I've had enough of hope & chains.

            Comment


            • #7
              Re: Need Part Number

              I posted a possible varistor test method in this thread: <a href="http://www.bowltech.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=2;t=002495;p=1#0000 18" target="_blank"><a href="http://www.bowltech.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=2;t=002495;p=1#0000 18" target="_blank"><a href="http://www.bowltech.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=2;t=002495;p=1#0000 18" target="_blank"><a href="http://www.bowltech.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=2;t=002495;p=1#0000 18" target="_blank"><a href="http://www.bowltech.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=2;t=002495;p=1#0000 18" target="_blank"><a href="http://www.bowltech.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=2;t=002495;p=1#0000 18" target="_blank"><a href="http://www.bowltech.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=2;t=002495;p=1#0000 18" target="_blank"><a href="http://www.bowltech.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=2;t=002495;p=1#0000 18" target="_blank"><a href="http://www.bowltech.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=2;t=002495;p=1#0000 18" target="_blank">http://www.bowltech.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=2;t=002495;p=1#0000 18</a></a></a></a></a></a></a></a></a> . I haven't tried it though.

              If you've seen as many triacs fail without varistor protection as those with protection, then that's good statistical evidence that the varistors aren't worth it (in that application).

              I only recall replacing one varistor in a SS chassis in the last 10 years (which suprises me actually). All our chassis have varistors on the contactors. I have never replaced an OmegaTek output triac, and I don't recall ever replacing an older 5-board output triac (but that's going back a long time, so I probably just don't remember). However, because we have always had varistors, I cannot compare to not having them (in this application).

              Len - sorry. I'm glad now I didn't use the phrase 'stochastic process analysis' (I was thinking of it). [img]/content/btubb/images/%%GRAEMLIN_URL%%/laugh.gif[/img]

              [img]/content/btubb/images/%%GRAEMLIN_URL%%/143.gif[/img]

              Cheers,
              Andrew.

              Comment

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