# Rectified mains question

Discussion in 'General Electronics Chat' started by oidium45, Aug 31, 2011.

1. ### oidium45 Thread Starter Active Member

Apr 24, 2010
130
8
I have a stupid question but I cannot seem to find the answer online. Everyone keeps telling me that rectified mains voltage (120vac) is 180vdc..
According to the math (assuming that mains is 120v and not 110v) It is more like 170vdc. Correct me if I am wrong here.

Vp=Vrms x (square root of 2)
Does a filter Capacitor after the full bridge rectifier make it 180vdc?

2. ### tom66 Senior Member

May 9, 2009
2,613
214
The actual range (from 100VAC - 127VAC) is 141.2V to 179.6V. So "140V" to "180V" is about right. Nominal voltage is 160-170V.

3. ### t06afre AAC Fanatic!

May 11, 2009
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1,222
Yes I would say you are correct 120x(square root of 2) is more like 170 volt than 180 volt. And the rectifier will also cause some voltage drop. So we may be talking perhaps closer to 165 volt.

4. ### #12 Expert

Nov 30, 2010
16,685
7,324
One more point...the capacitor will not boost the voltage. It will charge to Vpeak minus Vrectifier(s) then sag (under load) until the next power line peak happens. In Cally-forn-ya, thats one 60th of a second later for a simple rectifier and one 120th of a second for a full wave rectifier.

I'm talking absolute here. No fudge factors.

5. ### #12 Expert

Nov 30, 2010
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For a sine wave, volts peak = volts rms times the square root of 2.

I don't even know how you got a dc term into the equasion.

6. ### t06afre AAC Fanatic!

May 11, 2009
5,939
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The OP wrote
Which I would consider correct. So I can not see anything wrong wrong in the OP argumentation

7. ### #12 Expert

Nov 30, 2010
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Ionic had a post in between what is now post 4 and post 5. That is why you can't see who I was talking to.

8. ### t06afre AAC Fanatic!

May 11, 2009
5,939
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I see. I was somewhat puzzled by your post. But now I understand.

9. ### oidium45 Thread Starter Active Member

Apr 24, 2010
130
8
Thank you gentlemen I appreciate your input. It would appear that I was correct and was simply misinformed.