# Rectified mains question

#### oidium45

Joined Apr 24, 2010
138
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?

#### tom66

Joined May 9, 2009
2,595
The actual range (from 100VAC - 127VAC) is 141.2V to 179.6V. So "140V" to "180V" is about right. Nominal voltage is 160-170V.

#### t06afre

Joined May 11, 2009
5,934
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.

#### #12

Joined Nov 30, 2010
18,223
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.

#### #12

Joined Nov 30, 2010
18,223
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.

#### t06afre

Joined May 11, 2009
5,934
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.
The OP wrote
Vp=Vrms x (square root of 2)
Which I would consider correct. So I can not see anything wrong wrong in the OP argumentation

#### #12

Joined Nov 30, 2010
18,223
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.

#### t06afre

Joined May 11, 2009
5,934
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.
I see. I was somewhat puzzled by your post. But now I understand.