# How to calculate Toroidal Core Maximum VA capacity

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1. Jul 26, 2017

### SanPhysics

Hello Jimmy Lalani
Actual bare core dimension required for calculation, is your provided sizes are bare core or after transformer winding completed.please clarify.or proved primary and secondary VA rating.

2. Aug 2, 2017

### Jimmy Lalani

Hello San,
The transformer winding is already completed.

3. Sep 25, 2017

### Jimmy Lalani

Hello Hardy Sir,
I was just going through the conversation for calculating Maximum VA capacity. I found this conversation. In this you have taken e=230sqrt(2) cos(100t). I am a bit confused. Normally we take e=Em sinwt. Then why is it so here? Sorry , if it seems a stupid question to ask.

Jimmy Lalani

4. Sep 25, 2017

### jim hardy

That was just an example of starting with an assumed flux instead of an assumed voltage.
Flux and voltage have a derivative relationship, do they not ? One can ssume any flux one wants and voltage will be its derivative . I started with sine because its derivative has same sign. And san said he has 230 volts RMS.(not peak) where he is.

5. Sep 26, 2017

### Jimmy Lalani

Hello Hardy Sir,
Thank you very much. Now it is crystal clear in my mind.
However, if I assume Bm in order to calculate various parameters of transformer at the very begining, then later do I again have to find the new value? I asked few people and they said that my be I have to iterate until I get a suitable or final value? I could not understand what they meant? Can you please help me.

6. Sep 26, 2017

### jim hardy

I don't know why they said that.

If you make a good guess at how much flux density your core will happily accommodate, then the magnetizing current required to produce it will be reasonable. For that reason you need to be aware of you core's flux capability when you choose your operating flux density.
Since cores are available in discrete sizes and number of turns is an integer, you may have to adjust your Bm slightly to get your desired voltage with a standard size core .

Here's an example from the internet, worked out by what appears to be a methodical student with a lot of common sense and a good "Do It Yourself" mindset:
:
:http://engineerexperiences.com/design-calculations.html

here he shows pictures of the transformer he built and it's a pretty nice job................
http://engineerexperiences.com/hardware-design-.html