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LDR reads low (10K) in darkness?

Discussion in 'Electronic Basics' started by Bill Bowden, Nov 19, 2013.

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  1. Bill Bowden

    Bill Bowden Guest

    I repaired an outdoor dusk/dawn LED lamp that had a defective LDR used to switch the LED on/off. Problem was the LDR resistance read low (10K)in darkness, so I replaced it with one I had laying around and got it working. Since then (don't know how long) the same problem has returned with the LDR resistance again reading low in darkness. I checked a few LDRs in my spare parts and found one that also read low in darkness, which had never been used.Do these things go bad over time, and do they deteriorate sitting in the sun all day?

  2. Bill Bowden

    Bill Bowden Guest

    Thanks for that. The cell I replaced was encased in silicon rubber or something like that. I have one cell that appears to be encased in epoxy, so I might use that. I have some clear roofing sealer that is somewhat elastic when dry. Might try encasing a bare cell in some of that. The circuit switches at a resistance of about 27K ohms and the dusk reading of the cell is about 77K ohms. So, I was thinking of adding a 15K resistor in series with thecell so if it goes bad and only reaches 15K at dusk, the thing should still work?

  3. Bill Bowden

    Bill Bowden Guest

    No, I've never been on any mailing lists.

    I encased a small LDR in epoxy yesterday. I mixed a glob of glue and rolledthe LDR in it and then dried it slowly by rotating it every half hour or so. Came out almost a perfect sphere like a little marble. Now, all I have to do is mount it through the top surface so water doesn't get into the mainassembly.

  4. Oppie

    Oppie Guest

    Am I right that CdSe cells don't like DC operation? I seem to recall
    something from long ago about them working better long term with AC. Aside
    from that, these things were supposed to go extinct with RoHS, weren't they?
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