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Registered Member #3859
Joined: Sun May 01 2011, 03:47PM
Location:
Posts: 179
Microwave Oven Transformer setup -What determines the amount of Watts a transformer can pass through
Lets say that I decide to drive a MOT though the auxiliary winding that is used to drive the microwave generator heating filament. It is a thick copper wire wound on the core near the 120V winding.
Intuitively I know that the transformer will heat up and burn or I will cause a surge protector to pop out. But why?
What determines the rate at which a copper loop can convert electricity into alternating magnetic flux VS heat? What limits transformer designers (including Tesla transformers) to make primaries of many-many turns? Is it the magnetic permeability of the core? But how does it link to the amount of loops required to make the transformer efficient?
High frequency transformers have smaller cores because cores can transport more current as number of changes of flux per unit of time increases. But do high frequency transformers require more or less copper coils?
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
tarakan2 wrote ...
Microwave Oven Transformer setup -What determines the amount of Watts a transformer can pass through
Lets say that I decide to drive a MOT though the auxiliary winding that is used to drive the microwave generator heating filament. It is a thick copper wire wound on the core near the 120V winding.
Intuitively I know that the transformer will heat up and burn or I will cause a surge protector to pop out. But why?
What determines the rate at which a copper loop can convert electricity into alternating magnetic flux VS heat? What limits transformer designers (including Tesla transformers) to make primaries of many-many turns? Is it the magnetic permeability of the core? But how does it link to the amount of loops required to make the transformer efficient?
High frequency transformers have smaller cores because cores can transport more current as number of changes of flux per unit of time increases. But do high frequency transformers require more or less copper coils?
Basically, the answer to your question is the size of the core.
The bigger the core, the more 'volts per turn' before the core saturates at a given frequency.
I've been reading about 'volt-seconds' recently, basically, a core of a given size will saturate quicker the higher the voltage, but the inductance of the primary also plays a part, due to it's greater impedance.
Higher frequency = less copper
but higher frequency also means greater losses (more heating).
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
You should look up on transformer equivalent circuit and flux density calculations. There are basic formulas which answer all of your questions.
-The number of turns is set by voltage waveform, core area and peak magnetix flux density. If the flux density is too high, the core saturates and large no-load current is drawn.
-The maximum power throughput is calculated based on the equivalent circuit diagram, and basically is limited by total (recalculated) winding resistance and leakage inductance.
Registered Member #3859
Joined: Sun May 01 2011, 03:47PM
Location:
Posts: 179
May you recommend me a good book to read about transformer design? I would like to understand all those frequency-copper-core related matteers more in depth and see the formulas that are used to describe those relationships.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
At gigahertz frequencies, the building blocks of circuits change. You don't think in terms of capacitors and inductors any more, because you can't ignore the capacitance of inductors and the inductance of capacitors. You think in terms of waveguides, transmission lines, resonant cavities, antennas, stubs, tuning plugs, irises and so on. And you don't talk about voltages and currents any more, it is E and H fields.
You could make a thing that would behave like an air-cored transformer quite easily, and it would transfer power quite efficiently, but it would look nothing like a transformer.
Registered Member #3324
Joined: Sun Oct 17 2010, 06:57PM
Location:
Posts: 1276
Steve Conner wrote ...
At gigahertz frequencies, the building blocks of circuits change. You don't think in terms of capacitors and inductors any more, because you can't ignore the capacitance of inductors and the inductance of capacitors. You think in terms of waveguides, transmission lines, resonant cavities, antennas, stubs, tuning plugs, irises and so on. And you don't talk about voltages and currents any more, it is E and H fields.
You could make a thing that would behave like an air-cored transformer quite easily, and it would transfer power quite efficiently, but it would look nothing like a transformer.
Ive always wanted to learn about that stuff... but i have a feeling its extreamly complex and mathsy... not to mention expencive...
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Microwave Oven Transformer setup -What determines the amount of Watts a transformer can pass through
