[SOLVED] Parallel Transformers

[Raza]

Yes KerimF,
Both windings are in parallel. So one diode in each winding and one wire in common. There are two transformers are connected in parallel.

 

[KerimF]

As you wish Raza,

So to you, even if you insert a diode in series with a winding, the current can still flow in it in both directions.
Please note I am not talking about the two diodes output at which the two cycles are rectified.

Kerim

PS: You don't need to thank me later when you will understand and verify what I was talking about; DC current in each winding, unless we are taking about two different diagrams.

 

[E Kafeman]

KerimF, explain this:

DC current in each winding

???
It is half wave rectification, so current can only flow in one direction in the transformers secondary winding. The electromagnetic force is however still bidirectional without DC component. In reverse direction is load provided by transformer core as a kind of flywheel (Lentz's law).
I do not understand what you did wrote, can you clarify from were you got the DC source that can provide DC current to any part of the transformers?

 

[KerimF]

Hi all,

I see two separate transformers though they are connected in parallel at the mains sides.
In fact, in a house there might be too many seperate transformers said in parallel since all are connected to the mains lines.

Now let us try figuring out how each of these two transformers works. Please note their cores are independent even their primaries are connected to mains (quasi-ideal voltage source).
Each transformers has its secondary winding connected to load via a single diode. This makes a half wave rectifier.
When the diode is in its reversed state, I wonder how a current in the primary or the secondary winding of its transformer can flow (neglecting the relatively small magnetic current in the primary).

It is okay for me that all here see me wrong.
But does anyone already build the circuit (or just simulate it), insert an amper meter in series at the primary or secondary side and didn't measure any DC current when there is a load at the output?

Kerim

 

[dineshdeshmuk]

If the primary voltage of all the transformers is of same rating, you will connect all primaries in parallel and in Phase. Then you can connect the secondaries in series (all the windings must be of same current rating for safe working) as many as you need. There is no advantage of parallel or series over each other. If you connect secondaries in series it will add the voltage, like if you have three xformers of 5, 10 and 15 volts the result voltage will be 5+10+15=30 volts and the current will remain same as of ONE xformer. But if you connect in parallel thre xformers in parallel of 10 amps each (equal voltage of secondaries) the current will be added and yotal result current will be 10+10+10=30 amperes but voltage will remain same as of ONE transformer.

can we connect both primaries & secondaries of the transformers in parallel ?
can we connect both primaries & secondaries of the transformers in series ?

thanks

 

[E Kafeman]

But does anyone already build the circuit (or just simulate it), insert an amper meter in series at the primary or secondary side and didn't measure any DC current when there is a load at the output?

Assume that you feed the secondary side with with a half wave rectified signal and have nothing connected to primary side except for a volt or ampere-meter. Would there be any measurable DC-component?
No, a transformer is by its nature not able to transfer DC. You can easily test this by connecting a battery to one winding and measure voltage on another winding. The battery will cause a magnetic field in transformer core. Due to this field change induces a short period of current in the other winding. Same current but with opposite polarity occur when battery is removed as then is the magnetic field changing with same value as when battery was inserted.
Anyway, if the need of current is that high that two transformers are needed, is it less clever to not use a full-wave rectifier as a single diode will increase both resistive and magnetic losses and maximum output available power would be in same range as for a single transformer and a full wave rectifier. In this particular case with two parallel windings 2*15A will result in closer to 15A, not 30A average available current.

 

[KerimF]

Hi,

Just to complete the subject.
If the secondary winding doesn't have a center-tap, 4-diode bridge lets the current in the winding alternate hence the core flux will be symmetrical.
To add the currents of two transformers at the output, the two positive terminals of their rectifier bridge could be connected together, the same applies for the two negative terminals.
In case we have center tap transformers, only two diodes could be used as rectifier. Also the two rectifier terminals could be connected together if they are both positive or negative. Obviously the two center tap terminals need to be joined as well.
This configuration (when there is a rectifier at the transformer output) can be applied also in case there are 3 or more similar transformers and more load current is needed.

Kerim