Rules and Guidelines
Want to participate in the discussions? Please read our Community Rules and Guidelines. Need some help? Visit Support and Answers.

  • State Not Answered
  • Locked Locked
  • Replies 30 replies
  • Subscribers 32 subscribers
  • Views 3285 views
  • Users 0 members are here
Options
You may also be interested in
This discussion is locked.
You cannot post a reply to this discussion. If you have a question start a new discussion

DC on AC supply

nicemark
I have seen a number of videos which demonstrate the problems caused by DC currents on AC supplies with respect to RCD's. An issue which is apparently increasing with increased technology applications.  Please could someone explain how DC gets back into the neutral.


Almost all PSU's in all equipment begin with an isolating transformer. So getting a significant pulsed "dc" signal back that way is not impossible but tricky. (Pulses only occurring on one side of the cycle). 


My thoughts are that the DC is most often "created" by an unbalanced waveform, with a muted positive cycle, giving an overall DC flow.


Please could you direct me to, or give examples of how DC gets into the neutral, and/or just how much of an issue it can be in some homes.
Parents
  • 0
    Chris Pearson:
    Nathaniel:

    A generally accepted definition of 'dc' appears beyond what humans can agree on!


    Any current which is not alternating?


    For some reason, I am reminded of the brothers Jacob and Esau who were smooth and hairy respectively (Genesis 27:11). I quite like the idea of "hairy DC". ?




    That sounds one very reasonable definition.  Do we even agree on what alternating  means ... the word makes me think it must change direction regularly, not just fluctuate. In that case, half-wave rectified is not alternating, so it's dc. That fits with the 'pulsating dc' terminology, and with the need to specify 'smooth dc' if really meaning a steady value.  I don't have any strong opinion on what's best, and the above might be the most suitable or accepted within power or electrical installation terminology.  However, we've already seen here some different opinions of whether 'pulsating dc' is dc or ac. Spectrum-wise it's both - dc and multiple ac frequencies, added. In other electrical subjects there could be very different ideas: in electrical insulation studies 'dc' is sometimes seen as the situation of steady values, only approximately reached in practice.

    I like the hairy idea. It reminds me of descriptions of oscilloscope waveforms that have small hf noise on them.

     


Reply
  • 0
    Chris Pearson:
    Nathaniel:

    A generally accepted definition of 'dc' appears beyond what humans can agree on!


    Any current which is not alternating?


    For some reason, I am reminded of the brothers Jacob and Esau who were smooth and hairy respectively (Genesis 27:11). I quite like the idea of "hairy DC". ?




    That sounds one very reasonable definition.  Do we even agree on what alternating  means ... the word makes me think it must change direction regularly, not just fluctuate. In that case, half-wave rectified is not alternating, so it's dc. That fits with the 'pulsating dc' terminology, and with the need to specify 'smooth dc' if really meaning a steady value.  I don't have any strong opinion on what's best, and the above might be the most suitable or accepted within power or electrical installation terminology.  However, we've already seen here some different opinions of whether 'pulsating dc' is dc or ac. Spectrum-wise it's both - dc and multiple ac frequencies, added. In other electrical subjects there could be very different ideas: in electrical insulation studies 'dc' is sometimes seen as the situation of steady values, only approximately reached in practice.

    I like the hairy idea. It reminds me of descriptions of oscilloscope waveforms that have small hf noise on them.

     


Children
No Data

Join us to get the best from IET EngX.

Joining EngX lets you personalise your experience so you stay up to date on the topics that interest you, plus you’ll be able to make connections who are looking to collaborate, exchange ideas and more.

Join us Not now

Community Rules & Guidelines