Tape wound toroid for 40kHz

Clive Arthur · 2018-03-02T13:35:41+00:00

Happy Victory at Adwa Day. I need to make or have made a toroidal transformer with multiple turns to fit over a ~5" ~125mm conducting tube acting as a single turn through the middle. A ferrite core would be good, but finding the exact size would be difficult. Tape wound Silicon Iron as used on mains toroids sounds like the easiest way to fabricate one, but is there any chance of it working at 40kHz max or am I wasting my time thinking about it? Cheers -- Clive

Mar 02, 2018 23 Replies

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Clive Arthur 8 years ago

I'm trying to pick up and transmit a signal atop a few, maybe 20 amps DC in a tube (although it may as well be solid bar, I can't get to the inside). Frustratingly, I can't go into details. The tube is extant and non-negotiable.

So not a current transformer as such and with 40kHz maximum signal frequency.

This nano-crystalline and metallic glass stuff sounds interesting, but looks like a bit of a palaver to get hold of. Rogowski coils would be easy, but could one work as well as a ferrite toroid? I'm not sure why not, but, for example, current clamps use a coil with a core, don't they?

Not my strong point, magnetics. Then if it was, I wouldn't be asking here ;-)

Cheers

Clive

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Tim Williams 8 years ago

Ok, so what's you power, money and time budget?

This is all near field, but transmission laws still apply. Need it fast and cheap? Pump a lot of power into a Rogowski, recover the signal on the other side, and deal with the loss. You're up against the magnetizing inductance and DCR of the coil, same reason a current probe needs an integrator and usually a preamp too. How much power is actually required, depends on what size coil you can fit and the required link BW * SNR.

Need low loss (maybe for high efficiency power transmission)? Get a core of some sort. Need a lot of power? Get a big ferrite or nanocrystalline. Not as much? Maybe even a Rogowski would do (think of it as an RFID coil, make it resonant).

Tim

Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: https://www.seventransistorlabs.com/

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John Larkin 8 years ago

Oh, accuracy is no problem, which makes things much easier. Coupling efficiency could be mediocre. Rogowsky would probably be a bad choice to poke amps into your pipe.

Transmitting FM?

A pair of current clamps would be cool, if you can get one big enough.

There are probably non-magnetic ways to do this too.

John Larkin Highland Technology, Inc lunatic fringe electronics

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Phil Allison 8 years ago

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** Wide band audio transformers with silicon steel cores ( E, C or Toroidal) have been with us for many decades. The full power bandwidth is over 1000 times the low end saturation frequency - from say 25HZ to 25kHz.

The size and weight of the unit is set by the low end performance, higher frequencies take care of themselves pretty much as the magnetising current is proportionally less offsetting the other core losses.

.... Phil

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