ac

ws9876ws9876 Solar Expert Posts: 333 ✭✭✭
If you rectify 120 AC to DC and dont do anything else what DC voltage would you have??

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: ac
    ws9876 wrote: »
    If you rectify 120 AC to DC and dont do anything else what DC voltage would you have??

    You mean rectify with just one diode and no filter cap or rectify with a bridge rectifier and no filter cap?
  • solarixsolarix Solar Expert Posts: 713 ✭✭
    Re: ac

    If your rectify AC with one diode (Half-wave) then you get half-wave AC - just the positive part of the wave. The equivalent DC voltage is then 120Vac/2 or 60Vrms.
    Note that AC voltages are generally expressed as their RMS (Root-Mean-Squared or average effective power) value. 120Vac has a peak of 120*1.414=170Vpeak.
    If you rectify AC with two diodes on a center tap, or 4 diodes (bridge rectifier) you get full-wave where the neg. pulse is flipped over so both are positive. The equivalent DC voltage is then 120Vrms.
    If you add a big enough capacitor to the full-wave rectifier, it smooths out the ripple and lifts the output voltage up to nearly the peak of the AC or 170Vdc.

    So when the NEC says above 600V "nominal" is high voltage, does that mean that 440Vac with a peak voltage of 622V is high voltage?
  • BB.BB. Super Moderators, Administrators Posts: 29,241 admin
    Re: ac

    In general, the NEC/UL codes for power test with 3*600VAC=1,800 VAC "Highpot"

    In some cases, (such as when there are filter capacitors involved), we are also allowed to use a DC highpot:

    3*600 VAC * srt(2) = 2,546 VDC highpot

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: ac
    solarix wrote: »
    So when the NEC says above 600V "nominal" is high voltage, does that mean that 440Vac with a peak voltage of 622V is high voltage?
    No. The NEC is always talking about the "nominal" voltage, which for AC is RMS. So the 600V AC limit for "low voltage" and for residential wiring really means 850V peak. The same wire insulation could be used for 850V DC, but the NEC considers the peak voltage to be the nominal voltage where DC is concerned.
    That is just the way it is.....
    For the DC side of a PV system at a residence, you are limited to a Voc max (coldest temp) of 600V.
    SMA SB 3000, old BP panels.
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