Transformer design questions

  • Thread starter Harrison G
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Hello! Im studiyng for electrical engineer and i think its finaly time to build a transformer myself. I dont do this, cause i need one, but rather to learn how to design it. I'll be happy if you give me instructions how step by step to calculate one. Not how to physicaly build it, but to calculate the required number of turns and such.
So lets start with the fact that i have an E shape core. The frequency of the AC in my country is 50 Hz. Im thinking of powering it with 220V and the output voltage should be 110V. I dont want you to calculate it for me, i want you to tell me what steps to follow and such. Thanks! :-)
 

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  • #2
berkeman
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Hello! Im studiyng for electrical engineer and i think its finaly time to build a transformer myself. I dont do this, cause i need one, but rather to learn how to design it. I'll be happy if you give me instructions how step by step to calculate one. Not how to physicaly build it, but to calculate the required number of turns and such.
So lets start with the fact that i have an E shape core. The frequency of the AC in my country is 50 Hz. Im thinking of powering it with 220V and the output voltage should be 110V. I dont want you to calculate it for me, i want you to tell me what steps to follow and such. Thanks! :-)
So first of all, you need to be very careful and save when working with AC Mains voltages. It is very easy to be careless and get shocked or start a fire. So we will talk about general issues first, and cover some safety considerations in a bit (since you are not about to wind it up today). :smile:

What reading have you done so far? Are you familiar with how the turns ratio of the primary and secondary windings affects the steip-up/down ratio of the transformer?

And do you know what core material is used for AC Mains power transformers?
 
  • #3
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So far on transformers i have been studiyng them in Electrical machines. I know how they behave when the secondary coil is shorted, loaded and when no load is connected to it. I mean losses and such. I know the physics behind too. I also know that there is a ratio between the Voltage or turns of the primary and voltage and turns in the secondary coils, which is given by V1/V2=n1/n2. I have been teached how to troubleshoot a transformer too. About the core material, i think it was made of steel laminations, electricaly isolated from each other in order to reduce the Eddie current and thus to minimize the heat in the core.
 
  • #4
berkeman
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So far on transformers i have been studiyng them in Electrical machines. I know how they behave when the secondary coil is shorted, loaded and when no load is connected to it. I mean losses and such. I know the physics behind too. I also know that there is a ratio between the Voltage or turns of the primary and voltage and turns in the secondary coils, which is given by V1/V2=n1/n2. I have been teached how to troubleshoot a transformer too. About the core material, i think it was made of steel laminations, electricaly isolated from each other in order to reduce the Eddie current and thus to minimize the heat in the core.
All correct and good! :smile:

(and don't short out the secondary for real -- that will blow the fuse that should be in series with the AC Mains input to the transformer)...
 
  • #6
jim hardy
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but to calculate the required number of turns and such.
Have you any familiarity with magnetic units?
You'll need to calculate the Reluctance of your magnetic circuit , including the air gap
and the Webers of flux it'll carry
and at how many Teslas you want to operate the core.

Train your search engine . Start with 'transformer design'
mine returned for starters
http://ecee.colorado.edu/copec/book/slides/Ch15slides.pdf
http://www.edn.com/design/components-and-packaging/4369085/Using-a-power-transformer-at-a-frequency-it-wasn-t-designed-for

I';d wager @tim9000 could help .
 
  • #9
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Thanks all for the answers:-)
 
  • #10
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thanks @jim hardy , Yes Harrison, building a TX for yourself is a really good idea for an EE student, what year are you?
For something so simple transformers are very tricky to get one's mind around, and you'll find yourself coming up with paradoxes in your head, along the way to mastering the model.

There's a LOT of great literature on magnetic circuits and TXs so....
I suggest creating your own electromagnetic formula book, where you write down all your rules of thumb, that you need to keep reminding yourself of.
There may not be all that many formulas to remember, but there are a lot of different ways that they need to be considered, with a lot of implications and consequences that you deduce from their various incarnations. I have a healthy amount of english descriptions mixed in with the maths of mine. For instance I have various descriptions of what would happen to the various situations that the ideal model could find itself in (when the core is doing the work, when the coil is doing the work, voltage regulation, efficiency etc.) Something Jim has been a mentor for me with is understanding the dimensions in a more rich, useful, way. Like "Volt.seconds per turn as the cores flux capability", and V.s as the ability of the winding on a core to not saturate when blocking current (an inductor holds off ...volts for ...seconds) or keeping in mind the integral relationship of flux from voltage.

Don't be afraid to re-arrange the formulae, and keep the model in mind. You'll appreciate the significance of small things like resistance, that seem un-important in normal operation... understanding the various conditions like maximum inductance or saturation over permeability for various core materials and things like transients, aren't easy to hold in mind after you put the books down a couple months ago. That's why seeing it first hand on the bench is a really good idea.

P.S: Remember to use an isolation TX between you and the mains!
 
  • #11
jim hardy
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  • #13
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Thank you, guys! I will now study the links you gave me. I already have a basic idea on how to calculate it. I will start with the core area. Then i will find the turns per volt. Then the primary current(by the way do i need this current so i can figure out what gauge of wire to use?), the number of turns in the primary coil and the number of turns in the secondary coil.
 
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