Transformer question

[TsAmE]

I was curious, for a transformer why is it that increasing the voltage reduces the amount of current that is transmitted?

 

[Jony130]

Becaues Pin=Vin*Iin must be equal Pout=Vout*Iout
You can not take energy from nowhere.

 

[MrAl]

Hi,


Yes, and also more simply, there are really two ratios, the voltage ratio and the current ratio, and the current ratio is the inverse of the voltage ratio.
Thus, if you have a voltage turns ratio of 1:2 the output voltage gets stepped up to twice the input, but the current ratio is the inverse of that so it is 2:1, which means that the input current gets stepped down to one half of the input current.
One place where you see the current ratio have more importance is in the so called 'current transformer', where a current is measured and the level is stepped down and converted into a voltage with a resistor and that voltage is measured as an analog of the input current.

 

[colin55]

You are missing one important point.
For any transformer, it can only transfer a certain amount of energy.
This amount of energy is determined by the size of the core. That is, the laminations or the ferrite material making up the metal part of the transformer.
Suppose the transformer can only transfer 15VA. This is like saying 15 watts but we use the term "volt-amps" because we are talking about AC (alternating current) but it is actually alternating voltage.
We now have 15VA to play with and this can be provided by the secondary of the transformer as 15v and 1amp or 30v and 0.5amp or 60v and 0.25amp or 1v and 15 amp or 5v and 3 amp.
Provided the multiplication of the voltage and the current is equal to 15, any combination can be produced, even: 1,500v and 10mA.

 

[MrAl]

Hello there Colin,

I think you are too quick to criticize. Look at the first word of my post, "Yes". Gee, wonder what that could mean

 

[colin55]

He asked: "why is it that . . ." and you answered : Yes".

You failed to point out the fundamental reason why and how the current and voltage on the secondary side of a transformer are connected to each other via a formula.
He knows the answer is "yes." He wants to know why. You haven't explained WHY.

 

[mauricewarebee]

hi Tsame
i think your wonder in reduction of current is affected by this formula I=v/r. where i= current, v=voltage, r=resistance. when you increase voltage heating effect occurs increasing the resistance to a higher value leadin 2 reduction in current.
hey can u vote 4 my argument

 

[colin55]

when you increase voltage heating effect occurs

This is totally incorrect.
Voltage has no effect on heating. Heating only takes place when current is flowing. If the current increases, we consider that heating will increase. Generally, when a voltage is increased, the current will also increase but we NEVER associate heating with voltage. The current flowing in a circuit causes heating and the voltage is the "driving force" that causes the current to flow. We can say 10 amps flowing in a particular extension lead will create the same heating in the lead if it is connected to a 12v supply, 110v supply or 240v supply. Thus voltage does not come into the picture.

 

[MrAl]

You failed to point out the fundamental reason why and how the current and voltage on the secondary side of a transformer are connected to each other via a formula.
He knows the answer is "yes." He wants to know why. You haven't explained WHY.

Hello again,


Yes, you're still being overly critical here. My post came after Jony's post, not after the OP's post.
Lighten up a little

 

[mauricewarebee]

thanks 4 enlightening me colin55,
so now u've said wen u inccrease v current will increase also coz u,ve icreased its driving 4ce. so heating will occur.am i out of da way?

 

[koolguy]

plz tell How to calculate o/p power of Transformer Without measuring It's current.........?

 

[colin55]

Look at the size and type of transformer.
Go to other transformers of the same type and size and see if you can find their rating in VA.
Say it is 15VA
Now go to the transformer you have.
If the output is 15v AC, the current will be 1amp AC.
The voltage out will be 15 x 1.4 = 21v DC and the current will be 0.7 amp DC (after rectification).

 

[koolguy]

sory sir I don't have any Rating of It But I thick If I find It's resistance Then The calculated power will be true...........?

 

[crutschow]

sory sir I don't have any Rating of It But I thick If I find It's resistance Then The calculated power will be true...........?

You can not tell a transformer's power rating by measuring its resistance.
The transformer resistance is an undesirable (and unavoidable except if it has superconducting windings) consequence of the copper wire winding resistance.
This winding resistance is normally much lower than the load resistance to minimize power loss in the transformer.
An ideal transformer would have zero resistance.

 

[koolguy]

SO PLZ TELL how to find it's power with voltage & without current..........!

 

[Nigel Goodwin]

SO PLZ TELL how to find it's power with voltage & without current..........!

You've already been told, by the physical size and type of the transformer.

But the only accurate way is to measure the voltage and current, while monitoring the temperature of the transformer.

 

[koolguy]

Ok, as I have connected 104 capictor To the o/p of Transformer In parallel With It for Correcting power factor before connecting the capictor The Voltage was 100V After It was 110V & Pls Tell some More notable point for Power Factor...................!

 

[audioguru]

thanks 4 enlightening me colin55,
so now u've said wen u inccrease v current will increase also coz u,ve icreased its driving 4ce. so heating will occur.am i out of da way?

Please write in good English. Your spelling is horrible.

 

[koolguy]

I have seen some Inverter With Large Current & some With High Voltage What The Different In there working..........?

 

[audioguru]

I have seen some Inverter With Large Current & some With High Voltage What The Different In there working..........?

This thread talks about transformers, not inverters.
If you want to talk about inverters then please start your own thread about inverters.