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Samsung mobile charger difference in power

  1. Apr 21, 2011 #1
    Hi friends, I have a samsung mobile charger with specifications as
    Input: 150-300V AC and 0.15A
    Output: 4.75V DC and 0.55A
    So now by P=VI
    the input power is 36W (taking 240V AC and unity PF)
    and output power is 2.6W.
    So my doubt is why there is such difference the power of i/p and o/p??
    because if we have low i/p power we can have a less amount of energy consumed.
    Last edited: Apr 21, 2011
  2. jcsd
  3. Apr 21, 2011 #2


    User Avatar
    Science Advisor

    Re: Help plzz

    "Input: 150-300V AC and 0.15A"

    For many devices the input current rating is more of a suggested minimum rating for the power source you should use rather than an accurate measure of the typical current that the device will consume.

    BTW. You cant necessarily calculate the AC power as "VI" anyway.
  4. Apr 21, 2011 #3
    Re: Help plzz

    Thanks uart so from your reply i understand that input current is more than rated even then4 the input power is more. And even we take power factor into consideration it is more than output DC power. Now what i'm asking is can't we take the same amount of power which is consumed by the mobile and convert that from AC to DC to save such wastage of energy?
  5. Apr 21, 2011 #4
    Re: Help plzz

    Does it feel like a 20 watt as it's running? If not, than you may consider that it is not lossing so much energy. The safety agency ratings for current can be confusing and you generally cannot rely on them for power ratings. Also, the chance of such a tiny supply having power factor correction, are close to non-existent...
  6. Apr 22, 2011 #5
    Re: Help plzz

    Ratings like that don't necessarily denote the actual operating values of the device. Usually it would just be safe maximums or things like that. The only way to be sure of the power is to actually measure it while it is being used. I know there is a device called the Kill-a-Watt sold in the US that can measure the power taken from a wall outlet. I'm sure there are similar devices sold for your country.

    I find it highly unlikely that a charger would have less than 10% efficiency.

    Also, write better post titles. Generic things like "Help!" are useless and annoying.
  7. Apr 22, 2011 #6
    Re: Help plzz

    input current is only indicative for 150/300V source, actual current would be lesser. and charger efficiency should be >50%
  8. Apr 22, 2011 #7
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