Help plzz


by vidhyarthi
Tags: plzz
vidhyarthi
vidhyarthi is offline
#1
Apr21-11, 10:27 AM
P: 9
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.
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uart
uart is offline
#2
Apr21-11, 10:57 AM
Sci Advisor
P: 2,751
"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.
vidhyarthi
vidhyarthi is offline
#3
Apr21-11, 08:10 PM
P: 9
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?

Mike_In_Plano
Mike_In_Plano is offline
#4
Apr21-11, 09:15 PM
P: 557

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...
Jiggy-Ninja
Jiggy-Ninja is offline
#5
Apr22-11, 12:45 AM
P: 310
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.
aks786
aks786 is offline
#6
Apr22-11, 08:46 AM
P: 28
input current is only indicative for 150/300V source, actual current would be lesser. and charger efficiency should be >50%
vidhyarthi
vidhyarthi is offline
#7
Apr22-11, 08:09 PM
P: 9
I think i found my answer here http://www.physicsforums.com/showthread.php?t=492606
post 7 first paragraph
a charger is also same as AC DC adapter which does the same thing. am i right?


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