Iron Core Transformer Formula

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That looks like a very useful way of defining the wanted result.

I just ran 25 * 50mm core @ 50Hz sinewave and 900mT
and turn per Volt comes out at ~4T/V

Ai = 25*50mm (~2sq inches) for ~105W of secondary power (~115W of input power).

The very simplified definition I have used predicts 116W for a 25*50 core. VA = 31*(A^2) where A = core area in square inches.

Is Tu a toroid style core, eg. circular, or oval, or double U, etc?
 
E / I
T / U

used to be the two types of laminations that you could get for a standard transformer.Both fill in the B requirement in different ways.

B isn't some strange constant it's just what the keyboard had to offer to show a standard EI typre transformer.

If you remove the centre leg of E it becomes C or U. Then you need an extra leg of the I so it becomes T.
 
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There are more formulae involved in working out how much wire you can actually fit into the winding window.

Sometimes, if you need a VERY HIGH power transformer, you need to over specify the core just to give you the bobbin area to be able to physically wind the transformer.

As you are aware. Theory is great. Practicality is sometimes different.

At HV, care needs to be taken with insulation too. This can have a very dramatic effect on the amount of wire that you can fit onto the tranformer bobbin.

If you are winding by hand, I would allow at least another 50% just for the wire.
 
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I am not thinking about pushing beyond the limits of sensibility.

I am thinking:
Is the definition still accurate if the core is 1mm by 2mm?
Is the definition still accurate if the frequency is 580Hz instead of 50 to 60Hz?
etc.

The fact that FF, K & K' and B are included at different values shows that the definition has been compensated to take account of some/many of the practicalities. It is no longer, just a theoretical definition.
That is why I asked about limits, the practical formula may not hold true beyond certain size, or frequency, or material, or shape limits.
 
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The equations are still valid.

We were building 400Hz transformers.

You might have to be careful about the type of core material at higher frequencies though.

I used to be in the Royal Navy. We had a 400Hz transformer failure and had to swap in a 60Hz design. It worked fine.

Generally if you are going up in frequency (by 3 or 4 octaves) then the core will be OK. The same IS NOT true the other way. A 400Hz transformer will be terribly inefficient at 50Hz.

Sites selling transformer cores will detail what frequency they work best at.

At HF or EHF the maths becomes somewhat more complex due to the losses.

This was intended as an answer to supply related transformers 50 - 60Hz.
 
We are taught these theories at Uni. And, funnily enough they work. The Economists and Cheap manufacturers will always try to cut corners.

Why do you think that mains transformers in Mass Produced goods often fail.

It's down to the money counters trying to make things as cheap as possible.

In the DIY World we are trying to better them.

I recently disassembled a Far Eastern Electric Typewriter that had a failed mains transformer. Reverse engineering the maths the manufacturer was using over 3200mT as the magnetising flux on a cheap transformer. It was designed to NOT last.
 
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i build my traffos to run cool to touch.....

i run them at less than 0.9T and in some cases even down to 0.6T.....

diy'ers are not motivated by profit, we build them to our liking based on some needs.....

Exactly, that is why I recommend 780mT.

780mT is what is used in the MoD for long term reliability.

900mT is not too different and is well below the magnetic saturation level of the core.
 
Not in a single post, no. And not when you are shouting.

I would say look up SLUP121-127.pdf (filename) from Texas instrument , a collection of application notes which summarises the design of a ferrite switching transformer quite well.

When you understand the theory, then the formulas are quite easy.

Remember that a ferrite core switching transformer is limited both by saturation and losses.
 
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