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Small Resistor Value - Question

Discussion in 'General Electronics Discussion' started by Stocky, Oct 7, 2016.

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  1. Stocky


    Oct 7, 2016
    Hi everyone,

    I have a question about the voltage drop across a resistor with a small resistance i.e. <10 Ohms.

    My simple circuit to test this is a voltage source in series with a resistor. The resistor has a value of 4 ohms and is rated at 1W.

    If I set the voltage source to 1V I expect a 1V drop across the resistor. However with the 4 Ohm resistor the voltage drop is only 0.6V. If I use a 100 Ohm resistor instead it works as it should, a 1V drop.

    Can anyone please explain to me why this is happening?

    Last edited by a moderator: Oct 7, 2016
  2. davenn

    davenn Moderator

    Sep 5, 2009
    Hi there
    welcome to EP :)

    it may be measuring error with your meter

    what is the voltage source ?

    The other very significant possibility and the most likely cause, is that the 4Ω
    is loading down the PSU and causing a voltage drop on its output

    so with that in mind, were you using current limiting? if so, to what limit?

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