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What would be the effect If I change 4700uF capacitor to 18000uF?

Discussion in 'General Electronics Discussion' started by Prohor, Dec 3, 2016.

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  1. Prohor

    Prohor

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    Sep 27, 2016
    I have a dc bridge rectifier circuit to make ac to dc 50 volts output. It required two 4700uF capacitor, but I have 18000uF 70v in hand. If I use this 18000uF capacitor instead of 4700uF, will it damage my amplifier circuit- stk4231?

    Local electronic seller told that it will not effect if value is more than required, I have doubt ! please help.
     
    Last edited by a moderator: Dec 3, 2016
  2. davenn

    davenn Moderator

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    Sep 5, 2009
    that is correct





    Dave
     
    Last edited: Dec 3, 2016
    Prohor likes this.
  3. Colin Mitchell

    Colin Mitchell

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    The only thing that might happen is the fuse will blow.
    This is because the 18,000u will take longer to charge when the amplifier is turned ON and the fuse will pass a high current for a longer period of time and this will be seen as a short-circuit and it will gradually weaken and eventually die.
     
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  4. BobK

    BobK

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    Need a circuit diagram. If this is a bipolar supply, which they usually are for high power amps, then the two capacitors are connected to ground in the middle, and you cannot replace them with one capacitor, if that is what you thinking of doing.

    Bob
     
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  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    The change week have some effects.

    1) the ripple on the output will be less at a given current with the larger capacitor. This may reduce hum.

    2) the current surge at power on may be higher or longer. In the worst case this might blow a fuse but generally is not an issue

    3) the peak current through the rectifiers week likely increase. This may stress them more, but the duration will be less so the difference may not be significant.

    Making a
     
  6. AnalogKid

    AnalogKid

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    Jun 10, 2015
    I don't see the word "charge" in the thread title, post #1, or your quote. ?

    ak
     
  7. davenn

    davenn Moderator

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    Sep 5, 2009
    good point ,,, I didn't consider the possibility of a dual rail PSU

    @Prohor ... as you were asked show us a schematic of your supply
     
  8. Prohor

    Prohor

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    3
    Sep 27, 2016
    Thanks a lot. I was thinking something like this. As it is too much 18000uF, it should effect. I have tried with this and found 2 skt4231 IC damaged. I think it was charged too high and after switching off, it was releasing charge to be discharged too long. I have not found a power supply circuit diagram for stk4231 on google search. STK 4231 ic datasheet also not containing details about power supply.
     
  9. Prohor

    Prohor

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    3
    Sep 27, 2016
    Thanks for your reply, I have not found a power supply circuit diagram for stk4231 on google search. STK 4231 ic datasheet also not containing details about power supply. I have just tried a circuit like

    [​IMG]
    Re: I am having problem with image upload in this thread, is showing a "X" icon.

    url to image is: https://s15.postimg.org/66ipv52bv/20161205_134828.jpg

    and used four 1000v822j capacitor beside diode. Electronics seller told me that using 1000v822j capacitor will reduce noise during power switch on / off.

    I did not find answer from him about 'AN70MM' shown in the pcb.
     
    Last edited: Dec 5, 2016
  10. Prohor

    Prohor

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    3
    Sep 27, 2016
    I have an image of pcb.
    https://s15.postimg.org/66ipv52bv/20161205_134828.jpg

    I did not find a schematic of power supply in IC-STK4231 datasheet or for it in google search.
    I have a transformer to connect with this pcb ac input point, with output 35~AC, 7Amp.
     
  11. Cirkit

    Cirkit

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    Oct 28, 2015
    That power supply has split rails - positive and negative. You will need two capacitors as mentioned above in another post. If the exact value and voltage specification isn't available. you can go slightly higher.
     
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  12. davenn

    davenn Moderator

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    Sep 5, 2009
    thanks for that upload :)

    yes indeed it's a split rail supply so 2 caps as shown are needed
    You CANNOT use a single cap in that application


    Dave
     
    (*steve*) likes this.
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