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HELP!! What the hell is this piece?

Discussion in 'Power Electronics' started by jbear909, Sep 11, 2020.

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  1. jbear909

    jbear909

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    Sep 11, 2020
    Last edited by a moderator: Sep 11, 2020
  2. Martaine2005

    Martaine2005

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    May 12, 2015
    More than likely NTC (negative temperature coefficient) inrush current limiter.

    Martin
     
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  3. dave9

    dave9

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    Mar 5, 2017
    Agreed, it looks like an NTC thermistor, and after a long time those can wear out, but if you haven't found a fault downstream of it, then I would look for one before just replacing it... especially if you had two that failed simultaneously as that is just TOO coincidental, though I suppose it is possible that one had already failed and gone unnoticed before the 2nd one failed due to handling double the current. Normally only one is used not two in parallel.
     
  4. jbear909

    jbear909

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    Sep 11, 2020
    Sweet, how can I find the correct value?
     
  5. dave9

    dave9

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    Mar 5, 2017
    Use the info you have to track down the manufacturer or schematic. This does not look like a Motorcraft factory part, rather custom aftermarket for a limo.

    Without access to someone with this board or having a working board yourself, you're left to DIY estimating the value needed based on inrush and connected devices the board powers. There's various info out there. https://www.ametherm.com/inrush-current/selecting-an-inrush-current-limiter.html

    The size of the disc itself is a good hint at the current rating it had.
     
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  6. Martaine2005

    Martaine2005

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    May 12, 2015
    That’s the same link from Digikey I was going to use.
    The formulas can be quite brain numbing for people like me. Math is definitely not my strong point.

    Martin
     
  7. dave9

    dave9

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    Mar 5, 2017
    On second glance, this board looks a little like a rodeo cowboy (excessively bad) design where they just threw on way more capacitance than needed, which could cause an inrush current problem.

    Is it just the two 4700uF caps, or also 3 more near them, or are there NINE of them including the ones vertically oriented, all going through those NTC's?

    There's nothing that jumps out at me on that board which would need even 1/10th that much filtration. If something it powers (off the connectors) does, that powered device should be where the filter caps it needs are.

    I would investigate this and contact the company before considering to replace those caps (at least the two next to the NTC's) with 1/10th value caps and then you may find that you don't even need inrush current limiting, or at least there will be a lot less stress on it.
     
    Last edited: Sep 11, 2020
  8. jbear909

    jbear909

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    Sep 11, 2020
    Not sure, I had to put back in limo for the weekend, I can test on Monday.
     
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