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# How does a rectifier work? Answered

How does a full bridge rectifier work?I have seen some schemetics and they require 4 diodes and a capacitor right?I want to build one but can I use a 56uf 450v electrolytic capacitor to turn my mains voltage(240VAC)to DC.And will the output voltage be 240v?

## 4 Replies

I have an explanation of a rectifier here:
https://www.instructables.com/id/Hand-Crank-Flashl...

If working with diodes, there will presumably be some voltage drop, so it won't be a perfect 240 (is my assumption). You also need to consider how much current is being drawn as well and account for that.

A capacitor won't do the voltage conversion for you.

I have never built anything like what you are describing so can't give you any first-hand advise. That said, I would highly advise against starting with high voltage circuits when just learning electronics. You are better off buying a converter.

satheesh_240 (author)2017-11-02

If you want to rectify 240V AC to a DC, then the DC voltage would be 240*sqrt(2) = 340Volts.
Make sure that you use a capacitor of higher voltages for safety. (i.e 1.5 times the caclulated value). Use correct polarity while soldering. The diode should have at least 250V rating. I recommend using 1n4004 or 1n4005.
It's advisible to use a proper fuse when u connect ur circuit to the mains.

Lubomir73 (author)2017-07-31

A full wave, bridge rectifier will allow both the "positive" and the "negative" portions of the Alternating Current applied to it to be converted to Direct Current. This converts 60 Hertz AC to DC with a 120 Hertz ripple. The capacitor smooths this out by charging to the peak voltage and then discharging between peaks. As to the voltage output... Usually AC voltage is specified as an RMS value (Root Mean Square). Since AC varies between a peak voltage and zero, RMS is the heating value or working value of an equivalent amount of DC voltage. To calculate the peak voltage, you must multiply the RMS value by 1.414. So, 240 volts AC times 1.414 = 339 volts DC. This peak voltage (minus a two diode voltage drop) is what your capacitor will charge up to. So your DC output with no load would be a little less than 338 volts DC. And yes, do be so careful when working with potentially lethal voltages like this. One hand in your pocket or behind your back while you work. Also, discharge (short) the capacitor even when power is turned off to bleed off any residual voltage.

VitorT (author)2017-06-13

There is no need to use a capacitor if you want 240 volts DC from your mains, capacitofs are usually used in AC-DC converters to reduce noise on your DC signal, or to keep it constant. But if you are just rectifying the signal there is no need to use one. Just 4 diodes (that are rated for your voltage and current draw, 300v 5w for exemple).
CAUTION: if you are using mains voltage without isolation and the proper protection or knowledge of what you're doing be very careful.