Multisim rect' DC with 0V ripple! How to inject/simulate AC ripple please?

Discussion in 'General Electronics Chat' started by G.Beard, Jun 26, 2015.

  1. G.Beard

    Thread Starter New Member

    Jun 22, 2015
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    Hello!
    Firstly thanks for looking.

    I have 240 RMS > Fully wave rectifier > 170uF cap.
    200mA ILoad
    5% Vripple = 17Vpp

    The above is what I believe should be happening more or less. Im my sim I get 0Vpp.
    How do I introduce this ripple? I thought maybe I could slap another AC source 17Vpp into the mix but it seems a bit crude.
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    You have done the sim wrong...

    rect.GIF
     
    Last edited: Jun 26, 2015
  3. DickCappels

    Moderator

    Aug 21, 2008
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    Per MikeML you should see ripple if the simulation is representative of the real-life circuit.

    Please post circuit as shown in your simulator and also the simulation file. We might be able to spot a way to help you.

    Note: This thread moved to General Electronics Chat for better response.
     
  4. G.Beard

    Thread Starter New Member

    Jun 22, 2015
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    here is a screen shot, I am running my simulator in VMware fusion Windows 7 guest and my Mac will not let me upload the .MS14 Screen Shot 2015-06-26 at 14.13.37.png file.
     
  5. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    There is no ripple because there is no load current. The capacitor charges to the full line voltage on the first half-cycle, and there is nothing to discharge the capacitor. Try a resistor load, or a constant current source wired to discharge the capacitor.
     
  6. DickCappels

    Moderator

    Aug 21, 2008
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    As in 1.7k across C1.
     
  7. G.Beard

    Thread Starter New Member

    Jun 22, 2015
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    Hi, I put a pot across the cap until I got roughly 0.2A
    Please have a look at my file.
    Thanks.

    EDIT. That was the wrong one!
    Here is the one with the load attached.
     
  8. DickCappels

    Moderator

    Aug 21, 2008
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    Cannot open your files. How is the simulated ripple now?
     
  9. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Sorry, I dont do zip files...

    If loaded with ~200mA, the ripple should be about 11Vp-p
     
  10. G.Beard

    Thread Starter New Member

    Jun 22, 2015
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    Ok, so here is what I have.... Er, what did I get wrong tis time? :) Screen Shot 2015-06-26 at 14.48.46.png
     
  11. G.Beard

    Thread Starter New Member

    Jun 22, 2015
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    This virtual scope is not like my little Velleman pocket scope and I think maybe I will stop tis simulation stuff and just breadboard my experiments and stand back :)
     
  12. DickCappels

    Moderator

    Aug 21, 2008
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    You are looking at microamps and millivolts. You need to increase the current (decrease the load resistor) to get 200 milliamps, then you should see "better looking" ripple.
     
  13. Sinus23

    Member

    Sep 7, 2013
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    Don't breadboard this circuit!:eek:
     
  14. crutschow

    Expert

    Mar 14, 2008
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    Yes, the next room would be good.
    Never experiment with line powered electronics. It's way too dangerous. :eek:
    Always use an isolation transformer for such testing.
     
  15. G.Beard

    Thread Starter New Member

    Jun 22, 2015
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    I have an isolation traf with a variac in front of it.

    The pot I used in the sim had the wiper tied to another leg and was NOT set to the full 2M value. I just trimmed it wound. I would not attempted to recreate this circuit in the same way in real life... I like my life!
     
  16. G.Beard

    Thread Starter New Member

    Jun 22, 2015
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    Screen Shot 2015-06-27 at 09.05.47.png Hi, I have another question. The first attachment, how do we calculate the average current draw over time?
    Here is the exact same circuit in LTspice, except for the 2M pot that I dialled to 1k695 in multisim.... I used a fixed resistor in LTspice. When I used LTspice I got the exact results I was expecting. But Screen Shot 2015-06-27 at 08.44.17.png Screen Shot 2015-06-27 at 08.44.29.png Screen Shot 2015-06-27 at 08.46.09.png
     
    Last edited: Jun 27, 2015
  17. DickCappels

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    Aug 21, 2008
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    There are large differences between the ideal voltage source in LTSpice and the output of a real-world transformer. The transformer effectively has resistance and inductance in series with its secondary, which means it takes longer to restore the charge in the capacitor.
     
  18. G.Beard

    Thread Starter New Member

    Jun 22, 2015
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    Ok, I understand that this is a far more complicated matter in real world due to series resistance, inductance. I would like to get a very rough and ready idea of what size transformer I can safely use. Is there a basic rule of thumb?

    Thank you very much for your time, it is greatly appreciated.
     
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