Full Wave Rectifer !!

as all know there are two methods to obtain full wave rectifer :

1- using two diodes and using center tapped transformer
2- using four diodes only ( bridge )

but for using the second method i.e : using four diodes only ( bridge ) it must be the two terminals are live terminal , none of them are nuteral , as for 110 VAC a terminal must has 55 VAC and the second terminal must
has - 55 VAC , or for 220 VAC a terminal must has 110 VAC and the second terminal must has - 110 VAC

but at Egypt a terminal for these two terminals is a nuteral , and the second is variable between 220 VAC for positive half cycle and -220 VAC for negative half cycle

1- so i do not know how the full wave rectifer occurs if a terminal is a nuteral , specially we connect the negative output DC to this nuteral terminal , can anyone explain this ??


2- i do not know at the west country the two terminals are both have voltage or only one has voltage and the second is a netural like at Egypt , can any one tell me what is the connection there ??


3- for full wave rectifer using four diodes only ( bridge ) and the two terminals are live terminals as for 220 VAC as a terminal must has 110 VAC and the second terminal must has - 110 VAC , i reached to this result

a - for the positive half cycle : the output of the bridge which is DC is :
the positive DC is 110 V
the negative DC is - 110 v

which the different between them is 220 V

b - for the negative half cycle : the output of the bridge which is DC is :
the positive DC is 110 V
the negative DC is -110 v

which the different between them is also 220 V

are my results and my measurements correct or not at both the positive half cycle and the negative half cycle ???

4- if my resultss and my measurements are correct for above , it is very very wrong to connect the negative DC output to the ground because this negative DC output is not zero voiltage as it is - 110 v during both half positive and negative half cycle , am i correct or not ??


thanks

i think if we have a netural terminal as at Egypt , we can make also full wave rectifer by using two diodes only which are connected to the live terminal without using center tapped transformer

for the positive half cycle : the output of the bridge which is DC is :

the positive DC is 220 V
the negative DC is zero V

which the different between them is 220 V

b - for the negative half cycle : the output of the bridge which is DC is :

the positive DC is zero V
the negative DC is - 220 V

which the different between them is also 220 V

So it must be also not connect negative DC to the neuteral as it make short circuit

are my results correct or not ??

as we noted if we use a nuteral terminal the postive terminal for the output varies between 220 and zero while the negative terminal for the output varies also between zero and - 220 ,

while if we use the two terminals are live - no neutral - we found the postive terminal for the output is fixed to 110 V and the negative terminal for the output is fixed at - 110 V !!

Do this note correct or not ??

if my results are correct then we do not need the two diodes which are connected to the nuteral terminal to obtain full wave rectifer if there is a constant terminal which is the neutral , am i correct ??

magdyfayad said:

using four diodes only ( bridge ) it must be the two terminals are live terminal , none of them are nuteral

Click to expand...

It might be a language or terminology thing. but this statement appears to be wrong.

I believe a four diode full wave bridge can use a transformer leg that has been bonded to ground or not it makes no difference. In fact there does not need to be any transformer at all. In the states we call the leg of the transformer that has been bonded to ground "neutral".


On the other hand I might have misunderstood your meaning.

if you see any link which describes and draw the full wave rectifer , you find this links say during the positive half cycle the first terminal for AC is positive while the another is negative and during the negative half cycle the first terminal for AC is negative while the another is positive

show below







but if we use a nuteral , then this terminal is fixed voltage during both the positive half cycle and the negative half cycle , while the another terminal only vary from positive to negative !!

so my questions around to : do the measuring voltage at the positive terminal at the DC output vary during the positive half cycle and the neagative half cycle according to which type of AC voltage source i.e : contain nuetral or not contain nuetral ??

and also do the measuring voltage at the negative terminal at the DC output vary during the positive half cycle and the neagative half cycle according to which type of AC voltage source i.e : contain nuetral or not contain nuetral ??

as i noted if i use a nuteral terminal the postive terminal for the output varies between 220 at the positive half cycle and zero at the negative half cycle while the negative terminal for the output varies also between zero at the positive half cycle and - 220 at the negative half cycle ,

while if we use the two terminals are live - no neutral - we found the postive terminal for the output is fixed at 110 V at both the positive half cycle and the neagative half cycle , and also the negative terminal for the output is fixed at - 110 V at both the positive half cycle and the neagative half cycle !!


do this note correct or wrong ??


thanks

magdyfayad,

On this end of the language barrier, I think your confusion is with your use of the terms "center tap" and "neutral".


Or maybee It's my confusion

at your home , you have for sure single AC voltage source which consists of two terminals

if you measure the voltage of these terminals of this single AC voltage source with respect to ground what do you find ??

do you find a voltage at the both terminals with respect to ground ??

or do you find only at one terminal has a voltage with respect to ground and the another terminal has no voltage with respect to ground ??

magdyfayad said:

at your home , you have for sure single AC voltage source which consists of two terminals

Click to expand...

At my home if I look at the whole system we have 4 wires.
Line, neutral, line, ground, are their names
.

.

Neutral will be at the center, not zero.
With 120 VAC, If I use 2 diodes and a Neutral, I will have +170VDC half wave for the positive, and -170VDC for the negative.
120VAC is 170V peak, and 340V peak to peak.
Study Switch Mode Power Supplies (SMPS) for PC's and understand how the Voltage Doubler circuit works, and what the 100/220 jumper does.

what is the voltage at your home between line to line ??

and what is the voltage at your home between line to nuteral ??

note : your drawing means the nuteral is connected to the ground which must be zero , while keithkyll said the Neutral will be at the center not zero !!

I did not say that! Neutral is zero - connected to earth.
USA AC is single phase, 120/240V.Neutral is center tapped. One leg to earth (Neutral) is 120VAC (RMS). Leg to Leg is 240 VAC.
Your 220 VAC is NOT 0-220V. It is -311V peak to +311V peak (220 * 1.414), a total of 622 Peak to Peak. Go study like I told you.

see this link for Switch Mode Power Supplies (SMPS)


http://www.smps.us/power-supply.html



show this figure





you find the input is two AC lines , the both have voltage , there is no nuteral connected

while at Egypt we have two terminals ,only one has the voltage which is the AC line and the another is the nuetral

Remember that any measurement is a relative on. I think in many of these discussions we are assuming that 'zero' is earth (or an earth referenced lead)

An assumption is that any DC power supply will be isolated by some type of transformer. In that case we can talk about the voltage relationships BEFORE the transformer and those AFTER the transformer.

In many homes in the United States the power comes from a transformer in the power distribution network. That transformer is center tapped with the center lead referenced to earth ground. Thus with earth ground (and this 'neutral wire' as a reference point we read 120VAC (nominal) between the neutral and each hot lead. There is 220 VAC between the hot leads.

After being applied to the transformer, on the secondary side, before any lead is attached to an earth contact then ANY wire can be referenced as zero. Also, after the isolation of the transformer, ANY wire can be connected to the earth ground forming our fixed 'zero' point.

So any discussion of voltages on the secondary side (either AC or DC - pulsing or not) must include a discussion of an earth point (if it exists). Otherwise the discussions have no relevance to each other.

yes , bernie_carltonwe also here at Egypt the power comes from a transformer in the power distribution network. That transformer is center tapped with the center lead referenced to earth ground. Thus with earth ground (and this 'neutral wire' as a reference point we read 220VAC (nominal) between the neutral and each hot lead. There is 440 VAC between the hot leads

as our homes and our factories like your homes except the value of the voltage as 220 instead of 110 , then we did not need four diodes to make full wave rectifer as two diodes are sufficent !!

so my question why if we want to make full wave rectifer we must use four diodes ??

magdyfayad said:

what is the voltage at your home between line to line ??

and what is the voltage at your home between line to nuteral ??

note : your drawing means the nuteral is connected to the ground which must be zero , while keithkyll said the Neutral will be at the center not zero !!

Click to expand...

magdyfayad, In Egypt you will follow the European or British standard Voltages and your power supply from the transformer in the street will be as per drawing (A)
4 wire grounded wye,
probably called STAR POINT in Egypt

Your voltages will be
A to B =380 volts
B to N =220 volts
N to C =220 volts
You probably only have 2 wires coming into your house, they will be an N along with an A, or B, or C, to give you single phase 220 volts.

Notice N is EARTHED at the transformer and probably earthed again at your house switchboard.

Mine in New Zealand also is as per drawing (A)

The North Americans follow different standards and I think drawing (C) is the closest
It is a Delta Transformer with one leg being centre tapped to create N and also note that N is earthed
A to B =240 volts
B to N =120
N to C =120

yes , you are Gil47 right at Egypt

and i think you are right also at Amerca

so if we use at homes or at our factories single phase 220 volts between N and A, or B, or C , how then the full wave rectifer occurs ??

must be also use four diodes ??

or may be two diodes are suffucent ??

thanks