My ferrite transformer is bigger than yours... eh well...

On a sunny day (Wed, 27 May 2009 00:20:56 -0500) it happened "Tim Williams" wrote in :

That is nice :-)

Aside from material inherent bulk resistance ( which is normally high enough not to be a problem ), what was that ?

Yes, that would be the case in a transformer.

-- due to the hugely increased level of spam please make the obvious adjustment to my email address

The reason is a combination. I had wound eight turns of bare copper strap, some of which rubbed off on the bare cores. Applied power and I got a hearty spray of orange sparks between the start and end turns -- I guess there was enough of a copper track between them to short.

If either had been insulated, this wouldn't have happened, of course. I don't really have a good way to insulate strap... could spray it with urethane or something I guess. Not great for corners though.. maybe wrap it with something?

The present wire, which is insulated with "mineral filled teflon" or something like that, of course works quite nicely.

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

Woven fibreglass tubing?

Cheers

Phil Hobbs

At the other end, ferrite cores are often epoxy-coated for insulation & winding protection. A Dremel with a diamond wheel knocks the sharp corners off cores, too.

Tim, I saw a pallet of ferrite toroids at All Electronics not too long ago--they were almost dinner plates, but... your dinner would fall through the hole.

New invention: dieter's toroidal ferrite plate. Reduces calories AND shields delicate organic foods from harmful cell phone RADIATION. Available at audio stores everywhere.

Cheers, James Arthur

Count the number of wires (bifilar passes) that pass through the core. Those are turns. I do not mean each wire as I know that you doubled it up. I mean the number of times that twisted conductor passes through the core, including the lead in/out. That count is your turns count. Regardless of how many times you counted when you made it, on a toroid, each pass is "a turn" in transformer talk.

Have the copper silver plated, and run it at high frequency.

I'll bet it likes 56 - 59 kHz.

Coated or not, they suck for HV. A corona forms on the core. Don't get me wrong, we used them all the time, but I did discover that some miniature HV transformers have some strange effects that would only be huge on a larger scale unit. Larger stuff is usually potted or immersed though.

On Thu, 28 May 2009 18:34:00 -0700, TheQuickBrownFox aka Archie the Asshole, stopped choking his withered chicken for a few minutes to write:

Hi Archie:

Are you ready to attempt the puzzle yet?

Fortunately these cores are already burnished or whatever, but that still leaves the surface in a chalkboard sort of state, perfect for rubbing copper for instance.

Hmm, I must be too late. I got these from All Electronics, as a matter of fact. These are the largest they currently offer (unless they just discovered a box of something else).

Tim

Yes? I know what turns are, and there are ten of them as I stated.

That would be difficult, considering the primary shown is coated in PTFE. (Unfortunately, it's already plated with nickel, which probably isn't great for skin effect, and definitely sucks for soldering.) The other hardware isn't important enough to matter, and a mere plated layer will have no effect under 10MHz. The skin depth is approximately the entire tubing (the 1/4" copper seems to be 0.02" thick).

What?

n

Seems to work fine with flyback transformers.

Funny, I wound my own little FBT the other day. 10T of ~20AWG litz followed by 500T of #37, on a small E-I core about 1/4" square cross section. Got it up to 3-4kV peak, before the filament winding started arcing through (I don't have any HV silicon, so I used a toob diode!). That's the fault of the 300V hookup wire standing off 6kV peak, since I didn't have space for a better insulated wire. That

37AWG wire gives a hearty sized arc, I must say.

Tim

When your turns count on your secondary climbs past 150 turns, you have to be mindful of proximity between additional turns, and the turns down near the lead in. Count up your volts per turn, and you can define how many turns are safe to be near each other with single strength mag wire.

Once you are above that number, you either want to add transformer tape, and start a new layer, OR use a segmented bobbin.

When you get up around 1400 turns of #53, proximities are very important, especially pre-impregnation, if any. The coating on that wire is thin, and yes, they spit highly excited electrons out pretty darn good! I was making 15kV from 3V in (that control circuit was a feat in and of itself). I think the transformer was making about 2500 Volts into the multiplier. It was a switcher though, not a flyback.

This is also why one will never see a Tesla coil that has a layered secondary. The second layer turns are several tens of thousands of volts separated from the first layer. Far too much for the insulation of the mag wire. It will fail every time.

We had miniature transformers that had 7 layers of #43 on it. Each layer was kept inboard from the bobbin faces a mm or so. It would be a flat single layer of turns, then a layer of transformer tape, then a new layer of turns. The layers had to be kept inboard so that the tape would seal between layers. It also allowed impregnation media to get in there.

Every time we wound with the turns all the way at the bobbin faces, there would be a turn to turn short eminent.

We had stuff that if you breathed "coffee breath" on the multiplier caps before potting it, it would fail.

Bank winding has other advantages, too. Take this for example,

About 20mH total inductance (all six in series), while having only about

80pF parasitic capacitance. Low enough to get a plate waveform like so: That's a 200ns rise/fall time, and yes, I said plate waveform. This inductor belongs to perhaps the world's first class D tube amplifier.

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

Amine sensitivity is quite common in acid-catalyzed curing systems. Chemically-amplified photoresist is like that.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net