Multimeter testing led

Discussion in 'LEDs and Optoelectronics' started by Mhsmith, Aug 20, 2018.

  1. Mhsmith

    Mhsmith

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    I am very new to electronics and I am trying to build a solar light for the garden. My question is I borrowed a multimeter from a fried and used for testing leads setting meter to diode connecting positive lead to anode and negative to cathode led lights up. Just received my own multimeter difference is it is auto ranging when I set it to diode and test led positive to anode and negative to cathode it shows OL reverse it it to negative to anode and positive to cathode it shows 0.5, I am somewhat confused it seems non logical. In the multimeter instructions it says diode check resolution 0.001v will supply the forward drop voltage. Operating current wmA Operating circuit voltage 1.48v. Is there someone out there why there is a difference and obviously the led does no light. All other meter functions seem normal.

    Any help please Martin.
     
    Mhsmith, Aug 20, 2018
    #1
  2. Mhsmith

    Audioguru

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    My Fluke multimeter has a maximum output voltage of about 3.0V for a diode test. It lights and shows forward voltage for most colors 1.8V to 2.5V but not some white and blue LEDs that have a forward voltage of 3.5V.
     
    Audioguru, Aug 20, 2018
    #2
  3. Mhsmith

    Wollowstone

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    Even if it is an auto-range, you may have to "select" the measure that you wish. As example, on ANENG(TM) AN8008, the same dial position can be used for Ohm-meter, Capacitor, Continuity and for Diode, and by default, it occurs to be on the Ohm-meter. You have, in this case, with the gold button, to switch to Diode "mode" to measure the diode forward voltage.
     
    Wollowstone, Sep 13, 2018
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  4. Mhsmith

    KJ6EAD

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    If you need to test LEDs for function, color or polarity, there are a few common methods that you should know about: a button cell, a 9V battery with a 1k resistor and a dedicated LED tester.
     
    KJ6EAD, Sep 13, 2018
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