AC(3 phase)/DC power conversions

Discussion in 'General Electronics Chat' started by ak52, Dec 23, 2015.

  1. ak52

    Thread Starter Member

    Oct 15, 2014
    Hello all,
    I have a few basic doubts regarding AC to DC power conversion calculations.
    Please correct me if i am wrong at any stage.

    Firstly, when we consider single phase AC system,as a rule of thumb we can equate both the powers like this
    DC power = efficiency * AC power or more precisely
    Vdc * Idc = efficiency * Vrms * Irms, -------(1)
    where efficiency is between 75-90%
    All good so far

    Now coming to a 3 phase system
    DC power = 1.732 * power factor * AC power or it can be re-written as
    Vdc * Idc = 1.732 * power factor* V * Irms-----(2)

    What is V in the above equation,is it the Line to Line voltage or Line to Neutral voltage?I think it is the Line to Line voltage but i would like to confirm it with you guys first.Also how would equation 2 look like if i would want to write it in terms of efficiency?
  2. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    How is the PS connected to the line?

    If you have a 4 wire / 3 hot + neutral and you connect your unit directly to these4 lines then you are using the line to neutral voltage.

    If you have a 3 wire connection just across the 3 lines then it is the line to Lin voltage. Usually this connection is done thru a transformer. The first way can be direct to the line.

    So to sum this up, go a schematic?
  3. ak52

    Thread Starter Member

    Oct 15, 2014
    No schematic,i got a bulky weidmuller 3 phase AC to DC power supply at work,and was wondering how the calculations are done.This particular power supply has 3 separate lines of phases ,a neutral and an earth connector.
    So if its a 4 wire system,the voltage is line to line ,and if its a 3 wire(without neutral) it is line to line voltage.
    Thanks for clearing that up.

    About the second part,can equation 2 be written in terms of efficiency,like in the single phase system?
    Many thanks