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Adapter size?

Discussion in 'Electronic Basics' started by Anonymous, Apr 25, 2004.

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  1. Anonymous

    Anonymous Guest

    Hey all,

    I have two Sharkoon CCFLs hooked up to the inverter that came with the
    package. Instead of putting that in my computer I want to use it with an
    external power adapter. It works great, only the adapter does develop quite
    a bit of heat. After 20 minutes it's hot..

    The adapter is rated 12V, 400mAmp, 4,8VA

    The inverter's info is:

    CCFL Voltage: 200~1000V (?!)
    CCFL Current/Inverter Output: 5mA
    Power: 2,85 / 0,3W
    Input voltage of inverter: 12V (DC)

    I thought those cold cathode things don't use a lot of juice, I never
    learned to do the math..

    Can anyone tell me if 400mAmp is too small? If it is, what do I need, a

    Thanks, Erik
  2. CFoley1064

    CFoley1064 Guest

    Subject: Adapter size?

    Hi, Eric. From the way you describe your problem, it sounds like you're headed
    in the right direction. A 12VDC adapter with a higher current rating will
    probably do the job. 1000mA sounds good.

    Good luck
  3. Soeren

    Soeren Guest

    Hi Eric,

    200V @ 5mA (200 * 0.005) is 1VA
    1000V @ 5mA is of course 5 times this - 5VA

    The voltage will start high and then drop once the CCFL tube strikes,
    but I cannot tell you how much it will drop.

    The inverter is not 100% effective, perhaps it is only 70% to 80% (or
    even lower). This means that you will have to divide the numbers with
    the effiency rating.
    It will then need an input power rating of eg.:
    1VA/0.7 = 1.4 VA
    5VA/0.7 = 7.1VA

    So your adapter of 4.8VA might bee too small.

    But, how many degrees are "hot" in your case ?
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