# Rectifying AC voltage

1. Oct 1, 2007

### darik

Hello,

I'm trying to build a 160VDC PSU and need some help rectifying 114VAC to 160VDC.

OK, first I'm in Ireland and the voltage here is 220V/50Hz.
The information given on the label of the transformer that I have is 3300watt 110v Center-Tapped to Earth - 2 x 16amp.

There are two wires connected to the transformer core and then earthed(center-tap) and two end wires.
The output measured from the ends is 114VAC and measured from the center tap to either side is 57 V so I guess the polarities of both ends are opposite each other +/- 57-0-57.

I was considering the circuit found here: http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/rectct.html but I can't find reasonably priced diodes here in Ireland. On the other hand, I have some bridge rectifiers rated 35A 400V.

If I connect a bridge rectifier to both ends the output is 107VDC??? Can someone explain way?

So my question is:
Is it possible to disconnect both center-tap windings - rectify each 57v using bridge rectifier - and connect them back together in series to get 150-160VDC. I know there will be big voltage drop because of the two bridges used.

I'll be thankful for any help, advice, or hint you may provide.

Ivan

Last edited: Oct 1, 2007
2. Oct 4, 2007

### NoTime

Most meters will have a problem measuring a time varying DC output.
If you put a capacitor on your bridge rectifier it will charge up to the peak voltage.

Warning the capacitor will still have voltage on it when you unplug the transformer.

How big a capacitor you will need for your PSU need depends on how much current you need to supply.

What is the peak voltage for 114vac?

3. Oct 4, 2007

### lilrex

Quick and dirty method of finding the peek voltage on line AC voltage is by multiplying the AC voltage by the square root of 2.

This will give you 161.22 minus the voltage drops of you diodes (somewhere around .6V) for 114VAC. Throw a capacitor on the rectified voltage and there you have it 160 +- VDC
Be careful cheers!

4. Oct 6, 2007

### darik

Hi,

I've disconnected the tap from the ground.
When I measure the rectified voltage I can see 160V for a part of a second and than the voltage drops to 104V. I'll have to find a big capacitor and see what will happen.