I want to create an inductor with a ferrite core of 2.2 mH, but I do not know the size of the core, the number of turns and the size of the wire. The maximum voltage and current of my work are 429 volts and 2 amps respectively . Thank you for introducing a document or book on the design of an inductor with a ferrite toroid core. Thanks for helping me.
know the size of the core, the number of turns and the size of the wire. Th e maximum voltage and current of my work are 429 volts and 2 amps respectiv ely .
with a ferrite toroid core. Thanks for helping me.
might be a good place to start.
Two amps through 2.2mH is storing 4.4mJ, which is a fair bit.
I've used RM14 cores for this sort of work.
On the most heavily gapped core you'd need 117 turns to get 2.2mH which is
234 Ampere turns. The magnetic path length is about 1.9mm - the path throug h the cores is longer, but gets divided by the permeability of the core whi ch is about a thousand-odd - so you get to 123 Ampere.turns per metre (whic h if memory serves won't saturate the ferrite - but don't rely on my memor y).You've only got 0.58 mm^2 of wire area to carry your 2 amps, which might no t be enough. The coils could get too warm - and if the ferrite gets warmer than it's Curie temperature, it stops being ferromagnetic at all.
You might well need a bigger core pair, which you would probably have to ga p yourself. Don't use metal shim!
The EPCOS application notes detailed this kind of calculation in more detai l, with lots of helpful tables, but you need to go through them yourelf.
The 479 volts is on the high side - enamelled wire is rated for 500V and do uble enamelled wire - which is freely available - it a little better.
The voltage between layers of wire will be less than the full 479 volts,and you'd need six layers of wire to fit 117 turns on an RM14 former, so that wouldn't be a problem but you might want to sleeve the wires after they com e off the coil.
-- Bill Sloman, Sydney
A standard ferrite will be better since toroid with distributed airgap typically has significantly higher core losses
Cheers
Klaus
Unfortunately, magnetics design is complex. The problem is, given the above, under-defined.
That depends on the magnitude and frequency of the AC excitation, which isn't stated. The "cool-mu" and equivalent mix toroids are excellent for some things, like power converters. Not your dad's powdered iron.
One trick to short-cut design is to find a catalog part that looks like it will work, and basically copy it. It will at least get you a starting point.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
Another trick is to find a catalog part that looks like it will work, and buy it. Find and buy several types.
--
Thanks,
- Win
I always prefer to buy magnetics instead of building them. An existing part could get one into the ballpark on size and weight for a custom design
Here are *three* generations of inductors.
The first two looked fine according to data sheets, but then I learned a lot about skin effect. And customer spec-ratcheting.
RevC is hand-wound on a custom mandrel (aka Sharpie Pen) and air+conduction cooled.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
It looks machine made. Why was it better?
--
Thanks,
- Win
ot know the size of the core, the number of turns and the size of the wire. The maximum voltage and current of my work are 429 volts and 2 amps respec tively .
tor with a ferrite toroid core. Thanks for helping me.
Actually it isn't. And John Larkin isn't going to be able to tell us where he thinks that the problem is "under-defined". It would be useful if the OP had included some suggestion of the frequencies which the inductor is goin g to be used to reject, but the obvious problems are going to be core satur ation and power dissipation, and he has told us enough to let us get going on them.
ypically has significantly higher core losses
John Larkin's favourite strategy. It lets him off doing any actual design.
-- Bill Sloman, Sydney
On a sunny day (Mon, 01 Jul 2019 08:47:41 -0700) it happened John Larkin wrote in :
That third link looks mechanical feeble if it gets hot it will unsolder itself, and if there is a lot of vibration it will unsolder itself too, maybe even pull the tracks of the board, is that bare copper end protected by sone stuff?
There is a spec that says the wire should go through the hole etc etc, but that was mil long ago, maybe it changed
Transformers are easy once you get the hang of it
I have a box full of various sizes Ecores, and some ring cores... You can get good ringcores from old PC power supplies.
Al, type of ferrite, L, number of turns.... power, saturation, OP will have to give a ciruit and more details.
Everybody does. Sadly, magnetic components aren't a flexible as resistors or even capacitors, so your chances of fidning a part that's close enough aren't great.
True.
I remember the thread, and suggesting a RevD based on nickel-zince ferrite core, which would have needed fewer turns of - potentially thicker - wire, which would have had less of a problem with skin-effect, but possibly more with core loss.
It clearly would have taken more design effort than John Larkin was willing to contemplate.
-- Bill Sloman, Sydney
I'm the machine! My mechanical guy is working on a proper mandrel.
The first two gens were Coilcraft parts, superficially in spec. Both got way too hot as the pulse rate went up; this is a kilovolt, 5 MHz pulse generator. The revB flat things should have worked, but their cooling is bad and there must be some proximity effect increasing skin losses. The hand-wound thing has spacing to reduce proximity and to let some air in, fat wire for more skin, and is conduction cooled, gap-pad to pcb vias to gap pad to water-cooled baseplate. Ugh.
Everything gets hot on this board, being pulsed this hard. Traces. Fr4 laminate. Capacitors. Even the output barrier strip got hot from dielectric loss.
There will be a rev D.
I talked to a Coilcraft engineer about this application. His wisdom is "This power magnetics stuff is hard."
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
The whole idea is to keep it from getting too hot. Heat is bad. Copper resistance goes up about 0.4% per deg C, which is practically thermal runaway.
Make me.
I considered a cored inductor here but nothing looked like it would work. I'd burn the paint off a powdered iron toroid.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
On a sunny day (Mon, 01 Jul 2019 10:46:40 -0700) it happened John Larkin wrote in :
Been a long time ago I designed for navy and army, but they were VERY precise in these things,.,, Always days of acceptance testing in some lab.
What I wondered is as you talk about skin effect why do you not used silvered wire? I use silvered wire for all RF coils.
As to coil formers, in the old days for example I used ceramic coil formers with a thread cut in it where the silvered wire was to sit, so it could not move about. I mean like this:
I've designed flight hardware for the Air Force and for NASA, but it's
10% design and 390% compliance nonsense. I don't want to do any more of that.It was long lore that solder should never be used as mechanical support, until Tektronix broke that rule. And now we have surface mount.
Silver only conducts a bit better than copper. I'm using #14 copper magnet wire, from Amazon Prime. Given skin effect, most of my copper is not being used. My skin depth is very roughly 10 microns. Litz is apparently not useful up in the MHz range.
Several smaller inductors in parallel would theoretically use the copper better, but this beast works.
We're making a winding mandrel, but the actual coil will be freestanding, like in the pic.
This pulser gets bolted to an optical bench in a big heavy laser. I don't expect vibration.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
It's mine too. I have a huge collection of different cores, and more important, bobbins, which are harder to get, many dozens of hours selecting and placing orders, many thousands of $$ of inventory. I've long since lost count of how many inductors and transformers I've designed, and after my technician passed, wound myself. I love finished custom-magnetic products, but I hate the process getting there, and will do anything to get out of it. Buying inventory products is best. I have a large collection of that stuff, all sizes. But it often falls short. Especially for HV work.
--
Thanks,
- Win
I got my 50-ohm kV pulse-picker to work to 5MHz, but my goal was 10MHz. Solved that by interleaving two of them at 5MHz each. Maybe that would work for you.
--
Thanks,
- Win
Actually, that would. I could sell twice as many! I'll mention that to the customer. My circuit seems to be hitting fundamental limits around
5M and 1KV, and it gets worse as V^2, or actually something worse than V^2. We need better fets.Mode-locked lasers typically run around 80 MHz, so a 10M picker selects every 8th pulse.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
mandag den 1. juli 2019 kl. 21.18.59 UTC+2 skrev John Larkin:
small smd parts is the exception, for heavy parts and many connectors the rule still holds
Often breadboarding, even with purchased inductors, is the best way to select one. Inductors are the least well defined parts that we deal with.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Yeah, the design rules are coupled interacting equations, and some of the limits (due to nonlinearities) are 'soft'. Magnetic materials have a LOT of tabulated data that needs consideration. Other characteristics are geometry-dependent and mechanics gets involved, too.
I tried a design once, after looking at a reference design: I couldn't figure out why they used such a large core (about five times the mass required), and I had a stash of surplus cores (twice the required mass, but higher frequency)... after some calculating (couple of pages, all told, of algebra and notes) I shrugged and wound some; for my signals, it all worked fine.
Later commercial designs DIDN'T use the oversize cores, were more elegant than my (clunky from surplus parts) units. I'll never know why the originals were so oversized. The 'look at an example' plan was not a good start.
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