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Old 5th January 2012, 11:08 AM   #81
AndrewT is offline AndrewT  Scotland
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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?
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Old 5th January 2012, 11:11 AM   #82
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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.

Last edited by KatieandDad; 5th January 2012 at 11:13 AM.
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Old 5th January 2012, 11:17 AM   #83
AndrewT is offline AndrewT  Scotland
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Thanks.

Have you tried a variety of test data to evaluate the accuracy limits of the formulae?

Could you change one of the K to K' ?

Any ideas on where toroid style cores fit into the formulae?
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Old 5th January 2012, 11:19 AM   #84
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We used it at Uni to build successful transformers.

Obviously the formulae builds a working transformer, if you want to push the limits of the core then that is up to you.

Some Jap Crap runs at over 1800mT. No wonder they fail.
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Old 5th January 2012, 11:22 AM   #85
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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.

Last edited by KatieandDad; 5th January 2012 at 11:25 AM.
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Old 5th January 2012, 11:24 AM   #86
AndrewT is offline AndrewT  Scotland
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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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Last edited by AndrewT; 5th January 2012 at 11:29 AM.
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Old 5th January 2012, 11:31 AM   #87
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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.
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Old 5th January 2012, 11:34 AM   #88
AndrewT is offline AndrewT  Scotland
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Thanks again.
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Old 5th January 2012, 11:34 AM   #89
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Looking through my old notes.

The only thing that changes is the Flux Density of the core.

At HF and VHF the core material becomes very important. But the maths is the same.
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Old 5th January 2012, 11:48 AM   #90
AJT is offline AJT  Philippines
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Quote:
As you are aware. Theory is great. Practicality is sometimes different.
the most sensible thing you said so far......
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