Circuit Help: Using a Diode to limit reverse current to fwb

Discussion in 'The Projects Forum' started by Daniel718, May 17, 2015.

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  1. Daniel718

    Thread Starter New Member

    Dec 27, 2014
    4
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    Hello,

    I am trying to design a circuit that allows me to switch between 110ac and 24vdc. My question: can i put diodes on the output of the fwb to limit the reverse current when its on 110ac. how can i ensure the diode doesn't fail on me? is a resistor needed with the diode? and what type of diode would best suit this circuit?

    Thanks in advance for any information/tips ex1.jpg




    ex2.jpg
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,544
    2,369
    D2 will be blocking in the DC mode.
    Max.
     
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  3. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Why are mixing AC and DC onto the same output wires?
     
  4. Daniel718

    Thread Starter New Member

    Dec 27, 2014
    4
    1
    The output wires will be going into the coil terminals of a relay socket. i want to be able attach ac/dc relays to the same socket.


    Thanks for the help. after removing D2 on MultiSim i am getting about 45vac through the fwb when on AC mode.
    would the 45v cause any problems to fwb? any other suggestions the prevent this? thank you once again


    ex3.jpg
     
  5. ebeowulf17

    Active Member

    Aug 12, 2014
    678
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    Why not just move the switches to the junction of the 110 and 24 supplies, just above where d2 and d3 were on your second drawing. Don't switch where the 110 source is headed (straight to relay vs into transformer.) Instead, allow 110 into transformer at all times and just switch relay coil between 110 and 24v rectifier output. Sorry no time to draw what I mean. Does the description make sense?
     
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  6. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    The proposed arrangement is hazardous. If S1 and S2 got flipped accidentally a 24V load could suddenly become live! Use separate sockets for the 110V and 24V relays; or else use a mains isolating transformer.
     
  7. Daniel718

    Thread Starter New Member

    Dec 27, 2014
    4
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    Thanks a bunch. the circuit attached is what i understood from your description, which should work. the switch in the circuit will be a 2 pole 4 position rotary switch. with this i should have no problems adding another output like 110vdc correct?

    ex4.jpg
     
  8. ebeowulf17

    Active Member

    Aug 12, 2014
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    That's what I had in mind. Also, I believe this arrangement makes d2 redundant and unnecessary.

    Depending on the intended purpose of c1, does it need to move? Do you want it there for dc output stability or for back emf absorption?

    Finally, Alec_t brings up a good point (and is far wiser and more experienced than I am.) You may want to reconsider this entire concept for safety reasons. Don't let my advice serve as tacit endorsement of any connections to live mains voltage. When in doubt, take no chances!
     
  9. DickCappels

    Moderator

    Aug 21, 2008
    2,653
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    Welcome to the AAC forum.

    In general, we do not allow discussions to continue if it seems that the discussion could result in anybody being harmed. This is one of those threads.

    The owners of All About Circuits has elected not to host discussions of transformerless power supplies.

    This thread is against the AAC forum rules, Terms of Service (ToS).

    Any kind of over-unity devices and systems
    Automotive modifications
    Devices designed to electrocute or shock another person
    LEDs to mains
    Phone jammers
    Rail guns and high-energy projectile devices
    Transformer-less power supplies (yes I see the transformer, but the load can be connected directly to AC).

    Terms of Service (ToS).

    Therefore, this thread will be closed.

    Please try to understand the reasons behind this action, and feel free to browse and use the forums.

    You might find answers to your questions in one of these forums:

    http://forum.allaboutcircuits.com/showthread.php?t=54400

    Another good forum that shares many of the same membership is http://www.electro-tech-online.com/ .

    Good luck.
     
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