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power rating of series and parallel circuits

Discussion in 'General Electronics Discussion' started by PRIYADHARSHINI, Aug 25, 2014.

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  1. PRIYADHARSHINI

    PRIYADHARSHINI

    137
    8
    Feb 6, 2014
    hi,
    1.how do we calculate the power rating for series connected resistors?
    2.how do we calculate the power rating for parallel connected resistors?
    3.which type of connection is mostly preferable ?

    thanks regards...
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    9,863
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    Nov 17, 2011
    1 and 2: For each resistor P=I²*R or P=V²/R. This is universally valid and independent from series or parallel connection, although it may be easier to use P=i*R for series connection (as each resistor has the same current) and P=V²/R for parallel connection (as each resistor sees the same voltage).

    3: This question cannot be answered universally. You have to take into account the circumstances. A series connection can withstand higher voltages, as the total voltage is distributed among several resistors. A parallel connection can withstand higher currents, as the total current is distributed among several resistors.
     
    Gryd3 likes this.
  3. Gryd3

    Gryd3

    4,098
    875
    Jun 25, 2014
    Formulas:
    V = IR (Voltage = Current * Resistance)
    P = IV (Power = Current * Voltage)

    Adding series resistors to get total resistance:
    Rt = R1 + R2 + R3 + ... + Rn

    Adding parallel resistors to get total resistance:
    1/Rt = ( 1/R1 + 1/R2 + 1/R3 + ... + 1/Rn )

    Please remember that the voltage across a single component may not be the same as the voltage supplied to the entire circuit.
    These formulas assume you can determine the voltage across each resistor individually to correctly calculate power rating.
    All example assume simple series or parallel circuits where there is two or more items connected in series or parallel and not any combination of both!

    *Harald is speedy
     
  4. PRIYADHARSHINI

    PRIYADHARSHINI

    137
    8
    Feb 6, 2014
    1.k.thanks for ur explanation.here i m using 2400M ohm and 1M ohm in series.power rating of this two series connected resistors are 7.5W.
    now i want to built equivalent series or parallel resistor circuit for 2400M ohm..
    if i built the equivalent parallel resistor circuit for 2400M ohm.then i will calculate the power rating as per ur previous post.
    it should have the same power rating 7.5W right?
    2.how will be the power rating when the resistors connected in series when compared to parallel?
     
  5. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    The total power rating is the same in both cases since for a total resistance of 2.4MΩ the power is P=V²/2.4MΩ. regardless of how the 2.4MΩ is constructed.

    If you construct the 2.4M from 2*1.2M in series or 2*4.8M in parallel, the power for each resistor will be 7.5W/2 since the total power is then distrubuted among two equal resistors.

    All, of course, assuming the 7.5W given initially by you are corrrect - which we cannot verify lacking knowledge of either voltage or current.
     
  6. PRIYADHARSHINI

    PRIYADHARSHINI

    137
    8
    Feb 6, 2014
    its not 2.4M ohm 2400M ohm that is 2.4G ohm..k in this case series and parallel resistor has the same value.if it is combination of different values means how can we calculate the power rating of each resistor?
     
  7. Merlin3189

    Merlin3189

    250
    69
    Aug 4, 2011
    Something odd going on here.
    7.5W in a 2.4 GOhm resistor would mean 134000 V across it.
    Even if at only 2.4 MOhm it is over 4000 V, which is at least conceivable, but you might still be more concerned about the Voltage rating of the resistors.
    In that case maybe a mixture with both parallel resistors might mitigate against a single component failure? (eg 4 of 2.4 M ohm, with 2 in series and that in parallel with the same.)
    If it really is G Ohm, you might want to worry about the resistance of the mountings or circuit board?
     
  8. davenn

    davenn Moderator

    13,552
    1,850
    Sep 5, 2009

    You REALLY sure about that ??

    never seen a resistor over 22 M Ohms or so
     
  9. Harald Kapp

    Harald Kapp Moderator Moderator

    9,863
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    Nov 17, 2011
    PRIYADHARSHINI:
    I just come to realize that this thread is about your 132kV high voltage project - the original thread of which I had closed. I will close this thread, too. 132kV are way too high to tinker with. You obviously do not have the necessary experience to deal with such voltages - otherwise you would not ask such basic questions.

    While people on this forum are more than willing to help, this has to stop were life hazards come into play.
     
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