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extra 10 volts why

jamroll

Oct 31, 2022
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HI just started in this great hobby built my first mains project but i have a problem i have a mains transformer 230v into a full bridge rectifier i get 20v dc thats great now then i put a 2200uf 35v capacitor across the output to smooth it out like i have seen on youtube then the voltage goes to 30v ? like i said just started so not to technical please thank in anticpation
jamroll UK PS do not have any load connected .
 

bertus

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Nov 8, 2019
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Hello,

Have a look at the attached PDF.
On page 22 you will see an overview of the relation between the voltages.
From page 34 you will see the effect of the capacitor.

Bertus
 

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crutschow

May 7, 2021
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i get 20v dc thats great now then i put a 2200uf 35v capacitor across the output to smooth it out like i have seen on youtube then the voltage goes to 30v ?
A typical voltmeter will give the average DC voltage of the rectified sinewave, which is 0.636 of the peak sinewave voltage.
When you add the capacitor, it charges up to the peak of the sinewave which is 1 / 0.636 = 1.57 of the average or 1.57 * 20V = 31V.
 

crutschow

May 7, 2021
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The average value of the rectified sinewave should be 0.637 of the peak value, not 0.636.
 

jamroll

Oct 31, 2022
7
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Oct 31, 2022
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Hello,

Have a look at the attached PDF.
On page 22 you will see an overview of the relation between the voltages.
From page 34 you will see the effect of the capacitor.

Bertus
thats very help full thank you i have lots to learn obviously.
 

jamroll

Oct 31, 2022
7
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Oct 31, 2022
Messages
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A typical voltmeter will give the average DC voltage of the rectified sinewave, which is 0.636 of the peak sinewave voltage.
When you add the capacitor, it charges up to the peak of the sinewave which is 1 / 0.636 = 1.57 of the average or 1.57 * 20V = 31V.
Very grateful thank you thats made me think a lot about capacitor effects
 

danadak

Feb 19, 2021
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Feb 19, 2021
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These might be helpful :




Regards, Dana.
 

crutschow

May 7, 2021
517
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May 7, 2021
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Below is an LTspice simulation of the two cases with a full-wave bridge:
Note that with the capacitor, the output goes to about 30Vdc (green trace) and without, the average voltage is about 20V (red trace and Waveform window).

1667570568585.png
 
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