The usual kind of mains transformer has a laminated steel core. Steel is a conductor, hence there's stray capacitance between primary and secondary via the core. With an air cored transformer, this path is absent so there is only the direct capacitance between the windings. When I made some rudimentary measurements on a split bobbin transformer, the removal of the core reduced the interwinding capacitance by around two thirds (from memory).
Ferrite was used in radio receivers at 445 KHz for the intermediate frequency amplification.
Typically ( 120db gain ) two tuned circuit stages implemented with ferrite core transformers, the cores where used for fine tuning.
I think, this became obsolete with PLL ( Phase Lock Loop ) techniques.
AM intermediat frequency is 445 KHz.
FM intermediat frequency is 10.7 MHz.
I have seen ferrite used at lower frequencies to implement high Q filters in the audio band with ferrite pots.
I have seen ferrite pots for DC to DC converters. That is close to power supply. But frequencies far higher than 50 Hz.
Typically ( 120db gain ) two tuned circuit stages implemented with ferrite core transformers, the cores where used for fine tuning.
I think, this became obsolete with PLL ( Phase Lock Loop ) techniques.
AM intermediat frequency is 445 KHz.
FM intermediat frequency is 10.7 MHz.
I have seen ferrite used at lower frequencies to implement high Q filters in the audio band with ferrite pots.
I have seen ferrite pots for DC to DC converters. That is close to power supply. But frequencies far higher than 50 Hz.
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Sure, no-one wants to use ferrites at 50 or 60Hz unless there are compelling reasons. And in general there aren't, for power applications. Signal transformers though are another matter - I've been winding ferrite cored signal transformers for a number of years. They're easy to diy and much cheaper than nickel/steel cored ones. Of course the flux limitation is still the major issue but with signal trafos we care much less about copper losses so using more turns of thinner wire isn't normally a big problem.
NiZn ferrites might be an alternative to air-cored transformers as NiZn material has high resistivity. I've not played with any cores made from this though so I'm just speculating. Of course to transfer any power it would need to operate well above mains frequency.
NiZn ferrites might be an alternative to air-cored transformers as NiZn material has high resistivity. I've not played with any cores made from this though so I'm just speculating. Of course to transfer any power it would need to operate well above mains frequency.
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Interwinding capacitance can be reduced by using an interwinding screen. The core can be grounded. More to the point, a typical power transformer iron core is poor at magnetic coupling at high frequencies due to eddy current losses. Air core (or ferrite) would not suffer so more interference could get in, not less. People already complain that toroidal transformers let though more rubbish than old-fashioned EI etc.
There were portable headphone amplifiers using supercaps... wonder if they are still being made
The "feeling".
But now I just use obviously fake-label capacitors from China, achieves the same effect, but cheaper.
The "feeling".
But now I just use obviously fake-label capacitors from China, achieves the same effect, but cheaper.
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This makes sense at first glance. But when you consider that a split bobin air-cored transformer is not likely to work at all you'd be looking at ways to increase coupling, per example with bifilar coils. And then you are back where you started with the parasitic capacitance.
Not that any kind of air-core transformer is practical at mains frequencies anyway.
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Facts, figures? Am i your personal assistant?
Took me about 15 seconds to google this. Enjoy
"Life: Typical batteries have 500-1000 charge-discharge cycles while supercapacitors can reach up to one million cycles. In vehicle service, batteries have a life expectancy of 5 to 10 years while supercaps can last for 10 to 15 years.
Took me about 15 seconds to google this. Enjoy
"Life: Typical batteries have 500-1000 charge-discharge cycles while supercapacitors can reach up to one million cycles. In vehicle service, batteries have a life expectancy of 5 to 10 years while supercaps can last for 10 to 15 years.
In post #33, I was asking how long they last on one charge.
Used as a battery, how long does it give power ?
I know, it is much less with super caps than with batteries, I wonder wether it is acceptable in some cases.
Well clearly if you're concerned about capacitive coupling between windings your last port of call would be bifilar wound coils.
Agreed - given that even ferrite cored is largely impractical.
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