If I ever have to build a custom choke, I know who to send my first message to!....You certainly have a lot of experience in magnetics, as do a couple of others on this thread...Pretty informative stuff....thanks...Ross (Too bad DM mucked up the thread!)
An air gap in the magnetic circuit.
Best regards, Spehro Pefhany
What you gonna do? Liberate me?
I aint got no oil.
Tim, XX.
On Sun, 21 Dec 2003 12:56:16 -0600, John Fields Gave us:
There is a difference between the clinical definition for the term, nd the offering by wire makers. Nobody wants a two wire configuration. That doesn't make it any less measurable in effect, therefore valid to call litz.
On Sun, 21 Dec 2003 13:00:10 -0600, John Fields Gave us:
Quoted from a reputable magnet wire maker: "The multistrand configuration minimizes the power losses otherwise encountered in a solid conductor due to the "skin effect", or the tendency of radio frequency current to be concentrated at the surface of the conductor."
Bury yourself in that, idiot.
On Sun, 21 Dec 2003 13:11:29 -0600, John Fields Gave us:
You an idiot. We just made a big linear, and it operates at 19kHz. Quite sufficient for skin effect to make a difference.
In fact, the solid wire choke made the unit fall out of spec on the ripple figure of 10mV at 1500V out.
We don't make toys.
Mmmmm... Maynards.
Best regards, Spehro Pefhany
On Sun, 21 Dec 2003 13:30:56 -0600, John Fields Gave us:
A few posts ago, you were telling me my seven strand wire was not a litz wire.
Screw you. Anything over one strand is litz configured, because the reason for doing it is to increase skin (overall surface)area. I have seen two strands make measurable difference.
We have a miniature 1/4" x 3/4" x 1 1/4" HV transformer that will not function in the circuit it goes into without a litz primary.
I made those proto transformers, and I made every configuration from a solid wire up to pro grade HF litz wire.
Two strands makes a difference, but the transformer won't start working right until at least five strands of primary wire are used.
It runs at 49kHz perfectly with litz wire.
The reason? Skin effect.
It will be a 50M piece order, so if solid wire could be used, it would.
The term for today is "crest factor".
It is the space between UU, EE, pot, PQ, RM or other two piece ferrite or stacked laminated cores. The energy in inductors made with high permeability material resides mostly in the field that passes through the gap, as does the saturation resistance during high amp turns operation. The core essentially couples the turns (carries most of the same field around all the turns) and focuses it through the air gap. If you design an inductor for some peak current and at the current it reaches some specific flux, and you wish to change that inductor to a higher inductance at the same current, you have to increase the gap size, first, to keep the flux the same at the higher amp turns. But increasing the gap lowers the AsubL value (inductance per sqrt turn) so you also need more turns than what it would have taken if the gap had not been enlarged. So under this constraint, the inductance is no longer proportional to the turns squared.
A more useful constraint might be that the total amp turns remain constant and the gap remains constant (also fixed peak flux) as you change the inductance by filling the window to the same extent with different wire sizes. Since the core geometry is constant, inductance proportional to turns squared holds. But the current capability goes down as the inductance goes up. Double the number of turns, and the current capability goes down by half, while the inductance goes up by a factor of 4. The resistance also goes up by a factor of 4 (twice as long a wire with half the cross sectional area for the same coil cross section). So the resistive losses at full current stay the same.
Going through the range of inductances possible for a given pregapped core using this rule shows the normal optimum use of the core as an energy storage inductor. If your required product of square root of inductance times current (which is essentially a constant for a fixed gap and fill factor) is more than any example for a given gapped core, you need a larger core. If your product is smaller, you are wasting a bit of the core's capability (which you may want to do to lower losses).
If you put a spacer between the halves of an ungapped core pair (or add space to a pregapped set), you get a different product of square root inductance times current for each gap, but there is a best gap for any combination (from a total loss standpoint) for any combination of DC and various frequencies of AC current. For large, high frequency AC applications, larger gaps are better from a core los standpoint because of the lower flux swings and the lower hysterisis losses. For DC current, the core losses are zero, so the smaller gap lowers the number of turns, allowing fatter copper and lower resistive losses. You just have to worry about saturation and inductance tolerance.
He does this often......that way he can quote "out of context"....kind of bizarre huh....anyone who reads the thread sees what is going on.....
On Sun, 21 Dec 2003 20:43:43 +0000, John Woodgate Gave us:
Twice the turns equals 4 times the inductance.
It is easy. There is a square in the formula.
On Sun, 21 Dec 2003 23:04:51 GMT, "Ross Mac" Gave us:
You sure are a goddamned idiot.
No. Inductance increases with the square of the turns.
RL
The usual monosyllabic troll response.......Have a nice day DopeMatter!
John, I looked back through the patents on such things (I didn't do a really thorough search). The earliest such thing I could find was US1996186 by Affel (ATT), filed in 1932. It's not described as "Litz" wire, but it does describe insulated twisted wires, as well as better solutions (what is now known as "Litz").
On Sun, 21 Dec 2003 18:16:41 -0600, John Fields Gave us:
Skin effect is measurable, and notable at lower than RF frequencies.
That depends on how one defines "pronounced". We save several points on both final operating power factor, and overall efficiency at full load.
Yes, it is.
At RF Freqs it wi be like 17 or 39 57s or such. Hardly something I'd wind my HV POWER switching transformers from.
I'm sorry but ten inductors, each wound with one thru ten wires in parallel, will exhibit skin effects when tested on pro equipment.
The frequency these skin effect differences in performance begin to appear is much lower than RF frequencies... Sorry.
On Sun, 21 Dec 2003 18:40:41 -0600, John Fields Gave us:
Yes, I do.
I read in sci.electronics.design that Paul Burridge wrote (in ) about 'Help winding my own inductor?', on Sun, 21 Dec
2003:Ferrites for frequencies below about 1 MHz are quite conductive. Ferrites for higher frequencies have a different chemical composition and are insulators.
PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.