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Voltage drop from supply

Discussion in 'General Electronics Discussion' started by Whitmey, Aug 24, 2015.

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  1. Whitmey


    Aug 24, 2015

    I (think) I understand the concept of a voltage drop across a resistor- it is the voltage needed to supply the amount of current flowing in a circuit with the resistor in place?

    But, when I was powering a motor, I set the power supply to produce 220 Volts. Yet when I increased the torque on the motor, the supply voltage decreased. I thought that the currant should have changed, not the voltage, as a power supply is meant to give a set amount of volts? Why does this happen?

    Many thanks.
  2. Ratch


    Mar 10, 2013
    Charge flows, current does not. Current exists or is present. "Current flow" literally means "charge flow flow". That is redundant and ridiculous.

    The decrease in voltage is probably due to your power supply unable to sustain that voltage at the increased current the motor wants. You did not say what the amperage was before and after the load was applied.

    Whitmey likes this.
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    power supplies are not perfect.

    you could be seeing
    • the effect of load on output voltage (load regulation)
    • or possibly you are overloading the power supply and as as consequence the voltage is dropping
    • or perhaps the power supply has a current limit that you are reaching and it is switching from constant voltage to constant current and as a result the voltage falls to prevent the current limit from being exceeded
    • or possibly the leads have sufficient resistance to cause a measurable voltage drop at the higher currents.
    Whitmey likes this.
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