Transformer primer

[diy_audio_fo]

I'm looking for a primer on transformers.
I've found "Electronic Transformers" on VIAS - Free Books on Electronics and Electrical Engineering that looks me very clear.

Can we consider it a one stop primer on transformers?

Any further suggestion?

Thanks
diy_audio_fo

[Enzo]

I can't imagine that reading it would cause any trouble. If you know little about them, then why not read it? The price is pretty good at free. If it leaves out some areas that interest you, then pursue it further.

And it might matter what you want to learn. Do you want to learn how to engineer, design, and specify transformers? DO you have demanding and esoteric circuits to serve with custom iron? or do you just want to learn how transformers work and how to use them? And how to chose one for your circuit?

[diy_audio_fo]

Dear Enzo,
many thanks for your answer.

Originally Posted by Enzo

If it leaves out some areas that interest you, then pursue it further.

It is just this the point. As I know very little about transformers I ask if it is - as a primer - a one stop point i.e all main points are covered or you can suggest further readings

Originally Posted by Enzo

And it might matter what you want to learn. Do you want to learn how to engineer, design, and specify transformers? DO you have demanding and esoteric circuits to serve with custom iron? or do you just want to learn how transformers work and how to use them? And how to chose one for your circuit?

Specify, choose and use them as power supply transformer at line frequancy is all I need now.

Thanks again
diy_audio_fo

[Enzo]

GO to the web pages of some of the transformer manufacturers. They often have selection tutorials.

[WAJIH]

Hi peoples

im designing a dc to dc converter with a dual polarity (+-30v) (+-6A) output.
i am using an example from Switchmode Power Supply For Car Audio
i just have trouble understanding one thing. please bear with me as i try and explain myself.

The transformer i will wind myself needs two primary and two secondary coils.
i will be applying 12v, 30A(car battery) to center tap of primary and need to get 30v and 6 amps. one for the positive rail and one for the negative rail.

I understand how to get the voltage and current on primary side of transformer. I also understand voltage on secondary of transformer. the only thing im not sure about is how on earth u can get 6A per rail when Faradays transformer equation clearly states:

v1/v2 = i2/i1
so..12A/30V = xV/30A
solving for x i get 12A on secondary.

now 12A cant be spilt to get 6A because i have two secondaries or does it??
then if so does the 30v output split so i get 15v on each rail?????????????

THanks for allowing me to confuse u
any help would be much appreciated

[Enzo]

Not sure about your question. Your load will determine the current. Your primary won;t sit there drawing 30A all the time. If you draw 12A from the secondary, that will transform to current through the primary in the ratio of the transformer.

You will be applying 12v to the primary, yes, but you won't be applying 30A, it will DRAW 30 amps when and if it needs them.


COnsider a plain old transformer, for example 240v primary and 24v secondary. The secondary is rated for 1A. That means ideally that the primary will draw from the mains 0.1A, but only when the secondary is loaded to 1A. Either side of the transformer is running 24 watts. If you connect no load to the secondary, then no current flows through it. And then no current flows through the primary either. You can't push current into the primary.

[WAJIH]

thanks 4 the reply Enzo.

from the same link [URL="http://sound.westhost.com/project89.htm"]. we have 360w in primary = 360 w from secondary (ideally 100% efficiency).

u see i want to build a 100W amplifier so having 360w from secondary is no good. so to design this still using 12v 30A input into primary i will adjust my secondary to give me a symmetrical 20v 5A (100w) output.

does this mean that since i have 360w goin in transformer and 100w goin out that this smps is only 28% efficient.

how would i get around this problem.
any help would be much appreciated

[tsmith1315]

Originally Posted by WAJIH

v1/v2 = i2/i1
so..12A/30V = xV/30A
solving for x i get 12A on secondary.

now 12A cant be spilt to get 6A because i have two secondaries or does it??

Consider the full output voltage measured between rails.

+/-30V = 60V

60V@6A = 360W output

12V@30A = 360W input


But heed Enzo's observation. You will NOT be supplying 30A to the input until the amplifier demands it.

[WAJIH]

yeah thanks 4 the reply Tim,

i understand it now but can u try and help me with the post i did after that.

cheers

[Enzo]

If I understand this question, you still DO NOT have 360 watts going in UNLESS 360 watts is being drawn from the output. (assuming for discussion ideal 100% efficient stuff)


Think of the wall outlet in your home. I assume 240v? And I have no idea what common curent breakers you have down there, so I will use 10 amps. A 10A breaker on a 240v circuit would mean 2400 watts - but only if something is plugged in and using that much. if you do not plug something into the outlet, there is not 2400 watts coming out of the empty wall outlet.


The idea here is that the powr at the secondary is AVAILABLE, not automatically used.

I believe you are thinking about it backards. You don;t start with 360 watts on the primary and have it somehow push 360 watts into some circuit. The circuit has to USE 360 watts from the secondary for 360 watts to flow in the primary. Just as your 2400 watt outlet on the wall of your home. You can plug a 100 watt light bulb into it, and only 100 watts will flow, not all 2400 of them.

Or put another way, if you install a larger fuse in an amp, the amp doesn;t get louder.

If you build a 100 watt amp, it will use 100 watts from the power supply. The fact that 360 watts are available doesn;t matter to the amp, any more than the extra power at the wall outlet matters to the 100 watt light bulb.