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Discussion in 'General Electronics Discussion' started by dorian, Oct 24, 2016.

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  1. dorian


    Oct 24, 2016
    Hello all!

    I'm not mother tongue speaker (and hence writer) and I'm facing a quite complicated problem which requires me basic electronics knowledge that unfortunately I don't currently have (hope to fill the gap soon o_O ).

    I need to electrically connect a small module (a closed box which contains some tools that I will use for a scientific experiment) to a bigger structure via a 9 pin sub D connector. The bigger structure will provide (via the first pin) a non regulate voltage line of nominal 28 V DC (min 20 V max 36 V). The power budget (the developer of the bigger structure wrote down exactly this) is 3W.

    I think that the budget is 3W for every hour. Does it make sense? Or is the budget the total amount of energy, not referred to a temporal unit?

    As I wrote above, I know that inside the small module there will be some tools that I will alternatively activate (for example a CO2 sensor that will take only one recording every single day). I've found, in the description of the CO2 sensor, the following: Current Consumption : Normal mode : 20mA, Peak : 200mA, Sleep mode : < 0.5mA.

    Let's suppose that the experiment will last ten days and in the small module there will only be a CO2 sensor; that the CO2 sensor will reach the consumption peak (200mA) for a second during each reading and it will be in sleep mode during the rest of the 10 days (<0.5 mA).

    Is it possible to asses how many W I will consume? Is it possible to asses if the power budget (3W) will be sufficient to carry out all the experiment? It would also be very nice for me to understand how to calculate everything and the relation between Watt and Ampere in this experiment

    Thank you in advance, I really need your help!

    Ciao e grazie!!!!
  2. BobK


    Jan 5, 2010
    Watts is not a measure of energy, it is a measure of power, which is energy used per unit time. So Watts per hour is a meaningless concept. If it was Joules (a unit of energy) per hour that would correspond to 1 / 3600 Watts since 1 W is 1 Joule per second.

    In terms of your project. If it uses 3W at 28V that means that it will draw 3 / 28 or 0.107 A or 107 milliamps from your power supply.

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