Adding rectifier output

Discussion in 'General Electronics Chat' started by kingofkeys, Aug 28, 2012.

  1. kingofkeys

    Thread Starter New Member

    Aug 28, 2012
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    Summary: Is there any way to add the outputs of two separate rectifiers?

    Details: I have two separate AC sources (different amplitude), each one has a 4-diode bridge + filter capacitor. So, I achieve two separate DC source: one is 5 volts and the other is 7 volts.

    Now, I want to combine them to give me about 12 volts. I tried connecting the outputs of each rectifier in series, but the rectifier with the higher voltage seems to work, while the other (lower voltage) rectifier does not work at all (why?). So, I am left with just 7 volts even if I connect them in series.

    How do I add the output of two separate rectifiers together?

    See image for more clarification.

    http://postimage.org/image/uuocc48qf/

    [​IMG]
     
    Last edited by a moderator: Aug 28, 2012
  2. crutschow

    Expert

    Mar 14, 2008
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    Your image does not show.
     
  3. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    the supplies will have to be operated 'floating' before you can easily put the outputs in series. (... will need to be isolated from ground)
     
  4. kingofkeys

    Thread Starter New Member

    Aug 28, 2012
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    The image link is now fixed.

    Kermit2: can you explain more about the output being operated as floating? There are two different AC source, they are not connected to each other, but I want to connect their DC outputs.
     
  5. crutschow

    Expert

    Mar 14, 2008
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    You connect the positive output of one to the negative of the other. Is that how you connected them?
     
  6. kingofkeys

    Thread Starter New Member

    Aug 28, 2012
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    Yes that is how I connected them. Just as you would a normal battery, in series.

    Note: I also have access to oscilloscope. I tried poking around with no luck. So if you have any troubleshooting procedure, then I can test it out.
     
  7. #12

    Expert

    Nov 30, 2010
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    Just draw a line through the letter, "C" and it should work. (Positive of the bottom one to negative of the top one.)
     
  8. kingofkeys

    Thread Starter New Member

    Aug 28, 2012
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    It does not. That is the whole point of this thread. If I do so (as my original post states) the rectifier with the lower voltage output seizes to work. In other words, only one rectifier works.
     
  9. crutschow

    Expert

    Mar 14, 2008
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    What are the "separate AC sources"?
     
  10. kingofkeys

    Thread Starter New Member

    Aug 28, 2012
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    I guess I haven't provided as much details as I should have initially.

    Let me expand:

    I have one primary coil, and two secondary coils. None of the coils circuits are connected with each other electrically. I am experimenting with wireless power transfer.

    I am receiving power from the primary coil via two separate secondary coils. Each secondary coil has a 4-bridge diode and a filter cap to convert AC to DC.

    That is what I meant when I said I have two separate AC source. Sorry for the confusion.

    I have already tried connecting the + of first rectifier to the - of the second rectifier and a load across the whole (essentially connecting them in series as you would with any regular battery). But it does not work. I know this because the load had 7Volts across it (It should have 5volts + 7 volts = 12 volts if the series connection did work)

    How can I connect the 7 volt capable rectifier output with the 5 volt capable rectifier output to give me about 12 volts? And, why does it not work in series? (is it because the higher voltage output causes the diode to forward bias in the lower voltage rectifier?)
     
  11. kingofkeys

    Thread Starter New Member

    Aug 28, 2012
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    Guys? Anyone? Could really use some help. The question is pretty basic: How to add the outputs of two rectifier. I guess the answer isn't to basic :p
     
  12. pilko

    Active Member

    Dec 8, 2008
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    Simmulates OK.
     
  13. #12

    Expert

    Nov 30, 2010
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    We all said it should work. Pilko said it simulates correctly. You must have a different problem, like how you have assembled it or whether the diodes you used work well at 25 KHz.
     
  14. crutschow

    Expert

    Mar 14, 2008
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    If you have two secondary coils on the same transformer then just connect the two windings in series and run them to one bridge.
     
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