led problem

Discussion in 'The Projects Forum' started by Quazar, Sep 25, 2013.

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  1. Quazar

    Thread Starter New Member

    Aug 12, 2013
    Hi: I recently built and wired some garden border lights powered by a normal 120v household plug. The leds nominal specs are: 3.4v and 20mah. There are 25 of wired in series. Using Ohms law I calculated the resistor value as 1650ohm. The closest one I could find was 2200ohm which is what I used. After completing the circuit I left it on for about 24 hours in my house. No problem so far, but wait, Installed the lights in the garden area with each light under a glass bottle. First night looked great. Second night (left them on the entire time) when I looked outside they didn't seem as bright so I went out to check them. Hard to do a brightness comparison but they seemed dimmer. The real quandary is that 4 of them are out but the rest of them are still lit. This seem contrary to series circuits. 1)How come most of them are still lit? 2)Why are some not lit? 3) Could there have been some sort of insulation damage from the soldering process that let moisture interfere? I would appreciate any feedback. Thank you, Tom
  2. wayneh


    Sep 9, 2010
    I suspect the problem is that, while your voltage is a nominal 120V, it's AC so that means ~170V peak-to-peak. So at the peaks, the LED current was enough to cause rapid aging of your LEDs.

    Worse than that, mains-direct LED projects are not allowed for discussion here per the terms of service.
  3. Quazar

    Thread Starter New Member

    Aug 12, 2013
    Thanx. As you can tell I'm an electrical newbee. Recalculating for peak voltage tells me to double the Resistor. I will try that next. I am also unaware of the terms of service agreement. Where can I peruse that so as to not cross borgers in the future? Tom
  4. #12


    Nov 30, 2010
  5. Quazar

    Thread Starter New Member

    Aug 12, 2013
    That's another great thing to learn. I would like to try the capacitor but how do I figure what capacitor to use? Tom
  6. Metalmann

    Active Member

    Dec 8, 2012
    The best thing for those lights, is replacing the original batteries.;)
  7. bertus


    Apr 5, 2008

    I am closing this thread as it violates AAC policy and/or safety issues.

    It will be MUCH safer to use a transformer or wallwart for isolation.
    Isolation is a MUST as you even want to use it outside.

    6. Restricted topics.

    The following topics are regularly raised however are considered “off-topic” at all times and will results in Your thread being closed without question:

    • Any kind of over-unity devices and systems
    • Automotive modifications
    • Devices designed to electrocute or shock another person
    • LEDs to mains
    • Phone jammers
    • Rail guns and high-energy projectile devices
    • Transformer-less power supplies
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