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Old 4th July 2013, 02:22 PM   #1
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Default Need some help understanding

Hallo all,
Plse help me understand this. I have a toroidal 500 VA with dual secondary outputs, 0-48, 0-48 VAC. When I connect them to a rectifier bridge, the voltage after the bridge is +- 45VDC on each winding. When I add 10000 uf EL caps after the bridge, I get 66VDC. So 48 x 1.414= 68.8VDC - 0.7Vd due to the bridge which is correct. My question is, why do I only get 67VDC after the caps are added ? I am using a Fluke true RMS meter.
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Old 4th July 2013, 02:45 PM   #2
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what are the tolerances of the capacitors you are using??
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Old 4th July 2013, 02:53 PM   #3
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Two diodes on each side of the bridge for a total of 1.4 volts drop.
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Old 4th July 2013, 03:03 PM   #4
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Vrystaat, not sure I understood your question: are you asking why don't you get 67VDC without the CAPS ?
If that is the case, it is because the average of a full-rectified is 2*Vpeak/pi=2*(48*1.414-2*0.7)/pi = 42V (assuming vdrop in each diode of 0.7V ).

When you introduce the CAP you'll get an almost DC output, whose average is near the rectified sinewave's peak value (~66V)
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Old 4th July 2013, 03:30 PM   #5
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Thanks to all, the lights suddenly came on !! It makes sense now.
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