Transformers

[f4cepl4nt]

Just a quick question: Lets say I have two transformers, one with a 2:1 voltage ratio and one with a 3:1 voltage ratio. If I were to hook these up so that the voltage gets increased twice, would the output voltage be 6 times as much as the input? Would the current follow the same pattern as well, being decreased by a factor of 6? Please answer these questions assuming no power loss...or give me an idea of how to estimate power loss in a transformer 

Basically I'm just wondering if it would work properly.  ;D

 

[cjk2]

Well, I can see your reasoning, but it is very hard to actually make this work.  The problem you run into is that the second transfromers sees many more volts per turn than it was desiged for.  This causes two problems: overheating in the windings due to overcurrent, and the biggest problem, core stauration.  If you saturate the core(by appily too much voltage to a winding of too few turns) the transformer will overheat and will not output anything useful.  There are two ways around these problems: 1. use larger cores, or 2. use a higher frequency to drive the transformers(the transformers must now be made of a good quality material. Iron will not work past a few hundred Hz's due to eddy currents, so ferite is the best choice.)  Although your idea would be a good one, due to the above reasons, it will almost always be a better idea to simply increase the ratio of one transformer to get the voltage you want, and not worry about using two.

I hope that cleared things up... Let me know if you need any more help.

Chris

 

[Awerohu]

i think your transformers will saturate after a while....

about the power losses...it will depend on type of load you used....am i right? otherwise its quite difficult to estimate the power loses....

 

[awright1]

The second transformer will either saturate immediately or will not saturate.  It is a magnetic, not a thermal phenomenon.  It may overheat, also, depending upon loading and possible saturation.

Well designed transformers applied within their ratings are among the most efficient items of electrical equipment.  Assuming they are well designed and are used within their ratings,  you can probably assume something like 95% efficiency.  That is, output power will be about 95% of input power.  Of course, things get worse when you draw output current in surges, as with a capacitor-input filter with large capacitors, or when you draw large output currents because more power goes into heat due to (I^2)R losses in the copper windings and the resistance of the copper increases with increasing temperature.

What is your application, or are you just trying to understand transformer theory?  By the way, yes, if you used one of your transformers to feed the second, and if there was no saturation of the second, and you were drawing no current, the output voltage would be 6 times the input voltage.  Input/output current ratio would be the inverse of the input/output voltage ratio except that you have an additional "magnetizing current" at the input that is independent of the load current.  This is the current you measure at the input of a transformer with no load on the secondary.

awright