Electronics > Projects, Designs, and Technical Stuff

60Hz Transformer Core Loss

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bdunham7:
So your current phase angle (theta) is arccos (0.31) or 72 degrees.  Look here:

https://www.electronics-tutorials.ws/transformer/transformer-loading.html

You can figure the resistive loss as I^2R (0.10A) x (0.10A) x (20.8R) = 0.208 watts.  The core losses are the balance.

The idle current is a significant portion of the full-load primary current.  This means the transformer is not terribly efficient at low loads and could be close to or in core saturation.  This isn't necessarily a flaw as some transformers are designed this way.  And being a bit over on the input voltage would make that worse.



floobydust:
Cheaper 60Hz transformers operate at high flux density- less iron and copper required, but core losses are higher and worse yet at high line. Between 115VAC and 125VAC, I have measured around 30-40% increase in primary current for 20-75VA transformers.
Several watts is dissipated with no load, worse nowadays with utilities having high mains voltage and transformer manufacturers competing on price.

langwadt:

--- Quote from: floobydust on July 16, 2020, 08:53:12 pm ---Cheaper 60Hz transformers operate at high flux density- less iron and copper required, but core losses are higher and worse yet at high line. Between 115VAC and 125VAC, I have measured around 30-40% increase in primary current for 20-75VA transformers.
Several watts is dissipated with no load, worse nowadays with utilities having high mains voltage and transformer manufacturers competing on price.

--- End quote ---

are there that many transformer supplies left, with the stricter no load and minium efficiency requirements?

floobydust:
Low cost is king and the "race to the bottom" leaves us with transformers that run hot and have terrible  regulation. I find it a PITA to design them in now because no-load current and % regulation specs are missing, to hide the cheapness. What I do is sample a few brands and chose the heaviest lol.

I used to stay with a particular good brand such as Hammond, but they changed to off-shore low cost manufacturing in Asia and quality went awry. I'm not sure why a coil-winding machine running in North America verses Asia is so different in labour costs.

I have used the big HPS Imperator machine tool industrial transformers when I need a conservative design in a control panel.

NiHaoMike:

--- Quote from: WattsThat on July 16, 2020, 04:23:56 pm ---Why do you care? It’s not like you can save much energy with a better transformer, those things are designed down to a cost point with the minimum amount of copper and iron required and efficiency is low on the list of concerns.

--- End quote ---
That's most certainly true for an aftermarket replacement part, but for a part designed to be integrated into a product, that can cause it to fail standby power requirements.

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