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I rectified about 14V AC to about 12V DC but 6 V AC simultaneously with 12V DC at the end! It was verified by two different tests, 2W10 is apparently just an unit jammed with 4 diodes. Rs means large resistors.

Test 1: 2W10 rectifier, Rs ---> OUT: 12.7 V DC and 6.0 V AC

Test 2: 4 pieces of "IN4004 pec616", Rs --> OUT: 12.0 V DC and 6.0 V AC

enter image description here

Questions

  1. Why do I get both V AC and V DC? I expected only V DC.
  2. How can I filter V AC out?
  3. Can V AC be a problem in circuits that only needs the 12 V DC?
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2 Answers 2

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I'm going to go out on a limb and take a guess that your other question about reading AC and DC relates to this question ..

If you're feeding regular AC through a full-wave rectifier (the four diodes you mention), the resulting waveform may well give you funny readings on ordinary DVMs. The waveform will resemble the absolute value of a sine wave, and still has enough AC character that a $50 DVM will likely show you a significant reading, albeit an incorrect one.

Using a DVM to try to figure out a circuit like this gets you into the murky territory of the 'true RMS' problem. DVMs are all over the map with regard to how well they perform at giving correct RMS readings. And even if you have a meter that's dead on, this number may not tell you what you really want to know. In situations like this, an oscilloscope is the preferred instrument, and you can get PC/USB based ones for under $100 that will perform admirably at AC line frequencies.

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  • \$\begingroup\$ +1 for using a oscilloscope, and not a multimeter. \$\endgroup\$
    – Johan
    Commented Jun 11, 2010 at 5:33
  • \$\begingroup\$ tested it with oscilloscope, the point is a junction point with ACD and DCV characteristics. Adding a cap or a resistor to the point smooth the voltage. +1 \$\endgroup\$
    – hhh
    Commented Jun 11, 2010 at 20:59
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  1. You miss a cap: it charge and discharges so not allowing ACV, use eg "CK868 X 394K 50V A8722".

  2. Use the Cap in (1). Then, you will get something like 18 DCV and 0 ACV. The 6 ACV and 12 DCV got to 18 DCV.

  3. Probably.

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  • \$\begingroup\$ Did you answer your own question? \$\endgroup\$
    – Kellenjb
    Commented Jun 10, 2010 at 14:15
  • \$\begingroup\$ He answered his own question within an hour of asking with a very very basic answer... \$\endgroup\$
    – Kortuk
    Commented Jun 10, 2010 at 17:15
  • \$\begingroup\$ It is not a case of know better. It is a problem that you posted before thinking about, immediately recognized, then posted the answer. \$\endgroup\$
    – Kortuk
    Commented Jun 11, 2010 at 20:16
  • \$\begingroup\$ Kortuk: very well but I sensed something missing as the accepted answer revelead \$\endgroup\$
    – hhh
    Commented Jun 11, 2010 at 21:01
  • \$\begingroup\$ "CK868 X 394K 50V A8722"? What kind of specification is that!?? \$\endgroup\$
    – stevenvh
    Commented Jun 17, 2011 at 12:00

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