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A question about the Watt

  1. Jan 5, 2008 #1
    If I have 2 electrical adapters for a specific device, which has the following information on them:

    1- 230va/50hz/20mA

    2- 230vac/50-60hz/65mA
    ps66/2061 IP40
    IEC60950 T45/E

    How can I know, how many watts each of them require?

    I know that the watt = Volt x Amp. but I have problems converting the units and getting the final accurate result.

    Please help.

    Thank you
  2. jcsd
  3. Jan 5, 2008 #2

    Doc Al

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    Staff: Mentor

    (1 Volt)*(1 mA) = 1 mWatt
  4. Jan 5, 2008 #3

    Shooting Star

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    Homework Helper

    Consider problem 1. The appliance can be either connected to AC 230 V at 50 Hz, and 20 mA should flow. P = 230*20 mW = 4600 mW.

    But if it's connected to 4 V DC, the current is 150 mA, and the power drawn is 600 mW.

    How can the same appliance draw different power if it is to function properly? Unless, there is the cos phi factor in the AC, which decreases the power in AC.
    Last edited: Jan 5, 2008
  5. Jan 5, 2008 #4
    Thank you gouys for your reply and help.

    Shooting star, regarding your question. I don't really know. I have just copied what was written on the adapter. It's an adapter for a IP phone which is a gift from a friend in Sweden, and I live in USA, that's why am asking about the watt, becasue I wanted to use a converter to convert from the 220-240 volts of Europle to 110 volts of the states.

    Thanks anyways.
  6. Jan 5, 2008 #5

    Shooting Star

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    Oh, then you just go and buy an adapter. Ask in the shop. These are very common. The only thing which is still nagging me is that the frequency in US is 60 Hz.

    Also, I've never come across 4 V DC. Ask in the shop. If you buy an adapter which gives 4 V DC, that'd be the best. Look for power-in holes and see what they say.
  7. Jan 7, 2008 #6


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    Staff Emeritus
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    Gold Member

    I suspect that 4VDC @ 120ma is the OUTPUT rating.
  8. Jan 7, 2008 #7

    Shooting Star

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    Homework Helper

    That does sound most reasonable.
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