Aluminium bobbin for choke. Is this a common practice?

Hello All, How common are Aluminium bobbins for 50/60 Hz chokes and inductors? This is the first one I have seen.

I was at a ham radio field day recently and picked up a heavy duty coil which I thought might make a good choke for small home made rectifier unit for a small welder. I will add the iron core when I find some laminations.

The winding is aluminium strip 0.7 inches by 0.1inches. There are two strips of aluminium making up the 0.1 inch thickness. The strips are covered with some sort of fabric tape hand wound over the two strips. The whole winding is taped and painted so I can't see how many turns.

The hole in the bobbin measures just over 4 inches by 1 inch. The bobbin is 3.3 inches wide.

I didn't notice, since the whole coil assembly is covered in thick grey paint, but the bobbin is made of aluminium. I just assumed the bobbin would have been made of some sort of insulating material such as fibre glass or paxolin. An aluminium bobbin was a surprise to me. Is this a common practice to make heavy duty robust bobbins for low voltage applications out of Aluminium?

Regards, John Crighton Sydney

Reply to
John Crighton
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in article snipped-for-privacy@News.individual.net, John Crighton at john snipped-for-privacy@tpg.com.au wrote on 2/20/05 10:34 PM:

It is difficult to get a good idea of your actual problem without photos or diagrams. Unless I am missing something, aluminum bobbins for coils are going to be trouble. They are shorted turns. Thus, you choc will turn into a transformer with the number of turns wound on the bobbin being the number of primary turns. You will have a single secondary turn that is shorted. The coupling coefficient may be small, but it is a transformer nevertheless.

Bill

Reply to
Repeating Rifle

It doesn't sound like a choke to me. Al is a such a pain to machine or cast, ($$) plastic is widely used. need a pix.

Reply to
Schweinkolben

I agree. The only way an Al bobbin would work is if it has a slot cut down the length of the hole and out the end faces to break the 'shorted turns'. The OP didn't mention such a slot though. As is often the case, "a picture is worth a thousand words".

daestrom

Reply to
daestrom

The coil appears to be a rather neat bit of creative engineering - better and lower cost.

as to aluminum as the conductor and as the core

conductor -

1) The conductor in an inductor can be any material, since it is the orientation of the current, not the wire material, that does the work. An aluminum winding will work.

2) And if you wish to get the oxide deep enough, I think it aluminum oxide is a fairly decent insulator. Aluminum welding machines use a high frequency low current high voltage rider on the AC/DC power to punch through the aluminum oxide for the low voltage power flow. It would have to be fairly deep oxide, I think, architectural grade or better anodizing. The tape would keep it from scratching both in handling and thermally.

3) Theory says the extruded rectangular shape you can have from aluminum would let you get more field density than the round that copper is limited in drawn wire, and the coil would be more efficient.

core -

4) As I recall, aluminum is what is called paramagnetic (weakly magnetic). Where iron has a lot of its electrons oriented so as to spin in one direction over the other which then makes it magnetic, I think aluminum, nickel, cobalt, and a couple others have a few more spinning on one direction than the other, and they are called paramagnetic. (I would double check it in the book, but my kid borrowed it, and he has the book with the info in it over at the U)

5) plastic in a coil ain't necessarily air-equal plastic as much as it can be various levels of ferrite imbedded in the plastic matrix- some probably akin to the levels of magnetism of paramagnetic aluminum - remember that there is more available to fill a core shunt than the yes of iron and the no of air - including iron-aluminum "alloys".

putting a magnetic material in the core of a coil interferes with the magnetic field in that it :

-changes the coil's inductance according to the current carried and actually drops inductance to zero at core saturation, It probably takes a LOT of field to saturate a paramagnetic core

-decreases it to zero at certain frequencies so as to allow passage of those frequencies otherwise blocked by the coil,

-severely drops it in the proximity of the coil (so tesla coils, sensors, etc. use non-magnetic/air cores) , adds distortion and harmonics, reduces Q, lowers efficiency, reduces power handling, gives you the same inductance with fewer turns, lowers evil self-resonance, lower interference from stray field pickup, and it increases density near the coil proper.

Aluminum in a core will interfere less than iron, iron either as ferrite (oxidized) or as element. And andozied deep enough and not scratched, I am pretty sure it is non-conducting. And it can be extruded into shapes whose edges leave no gaps.

a fairly neat bit of engineering.

Reply to
--

AL losses are higher than copper, and it is the material that conducts the current.

Deep oxide is brittle and causes fractures on AL wire. If you bend it slightly, it breaks through the surface.

Ditto Copper. However extruding AL is more difficult that Cu, Cu is more malleable.

Weakly anti magnetic. It causes L to decrease as it is put further into the core. (at high F) At low Frequency it is "transparent" to magnetic fields.

nickel is magnetic.

need a pix of the gizmo.

Reply to
Schweinkolben

Hello All, the best I can do for a picture is to refer you to this site

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Half way down the web page there is a couple of pictures under Coil Formers or Bobbins.

My coil former looks like the one on the left hand side. On my former, the side cheeks are made of thin aluminium sheet. The dark orange centre piece is again made of thin sheet aluminium (not an extrusion) with folded up 3/4 inch tabs to hold the cheeks in place. To stop the cheeks falling off the edge of the centre dark orange section.

Just thinking about this coil. The fact that there was no iron core or scratch marks on the paint, it probably was never used or intended to be used for an iron core choke. The bobbin would be a shorted turn like you guys said. Not a good idea. I think someone has made this coil up and then realised, ooops! metal bobbin, scrap it! When I find some laminations to fit the 4" by 1" slot in the bobbin, I will experiment with the aluminium former and without it just for fun. All the hard work of winding the heavy conductor has been done, so tape alone will hold it together. I can still use the coil that way with a regular iron core.

Thanks for all your replies, and discussion. Regards, John Crighton Sydney

Reply to
John Crighton

The strange part is the AL wiring on it. Seems like 1960's vintage. They used AL wiring in houses back then for a while It could be made to get hot and stay that way, and plastics will flow over time. But it should work fine with 50/60 Hz. (if the coils are not shorted). Some big equipment uses transformers and chokes (weigh 25 to 300 lbs. each) thick painted gloss black, for vibration tables, AM radio stations, some medical equipment, etc.

Reply to
Schweinkolben

but in the small amount used in a coil, that difference would be negligible.

true about the oxide being somewhat brittle - I can't speak to fractures being caused by oxides on round wire and would imagine that would be possible, given the outer fiber deflection from the round shape turned in bending, but i find that unlikely on rectangular pieces, since the outer fiber stresses have more area to relax into in a rectangle than on a round. We never had any problem with fractures when anodizing and (generous radii) bending any of our rectangular architectural or exterior structural aluminum - mostly 6xxx and 5xxx series ( our sister companies were anodizing and extruding facilities).

Extruding aluminum is fairly easy and a common practice, in my experience. I have had, and seen, many complex shapes with sharp corners extruded. I was under the impression from our sister company that copper would not hold a sharp corner coming out of the dies like aluminum does.

Book is back from the U - According to Halliday, it is paramagnetic. also -

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lists it as a paramagnetic material

Being repelled by a magnet is referred to as diamagnetic in the physics text. It is present in all substances. See also the link above.

I stand corrected - iron, cobalt, nickel, gadollinium, and dysprosium are all ferromagnetic elements.

Reply to
--

you know Aluminum:

how long have you had them ?

An Aluminum bobbin may not do much under Normal Current conditions as you there suspect., but, betcha if you could keep boosting the =83requency to higher levels regardless Vin & control of Aout the circuit you'd get some notable results ....

aren't those used in signal buzzers?

Reply to
Roy Q.T.

Try Your Phyics: aluminum has an explicit conductivity.

you're to lost in electrical eng if you dare state it (Al) has no conductivity, perhaps you're taking the Clear Gel Subcoating of your sample for a given in your field.,

[a boost in =83 and you'll get the coil to sock or arc as customary]

pierce the sample and you'll differ such utterances....

Current: it will seem to stall under superfluos superresistive conditions but, believe it., it's there; perhaps in {another dimension or} frequency but it'll always be there if Voltage is applied.

sheesh how can he have said it doesn't conduct ....?

PARENTS: KEEP YOUR KIDS AWAY FROM THESE GROUPS !!!

IF YOU'RE [not] A KID:-) take care...this is a place where serious harm may result from misguided handling of products & information.

Reply to
Roy Q.T.

Try Your Phyics: aluminum has an explicit conductivity.

you're to lost in electrical eng if you dare state it (Al) has no conductivity, perhaps you're taking the Clear Gel Subcoating of your sample for a given in your field.,

[a boost in f and you'll get the coil to sock or arc as customary]

pierce the sample and you'll differ such utterances....

Current: it will seem to stall under superfluos superresistive conditions but, believe it., it's there; perhaps in {another dimension or} frequency but it'll always be there if Voltage is applied.

sheesh how can he have said it doesn't conduct ....?

PARENTS: KEEP YOUR KIDS AWAY FROM THESE GROUPS !!!

IF YOU'RE [not] A KID:-) take care...this is a place where serious harm may result from misguided handling of products & information.

Reply to
--

Try Your Phyics: aluminum has an explicit conductivity.

electrical or magnetic?

1) it does not conduct magnetic fields, although it is relatively permeable to magnetic fields

2). Of course aluminum is an electrical condcutor . Aluminum oxide, however -

you're to lost in electrical eng if you dare state it (Al) has no conductivity, perhaps you're taking the Clear Gel Subcoating of your sample for a given in your field.,

to what are you referring?

[a boost in f and you'll get the coil to sock or arc as customary]

pierce the sample and you'll differ such utterances....

Current: it will seem to stall under superfluos superresistive conditions but, believe it., it's there; perhaps in {another dimension or} frequency but it'll always be there if Voltage is applied.

sheesh how can he have said it doesn't conduct ....?

PARENTS: KEEP YOUR KIDS AWAY FROM THESE GROUPS !!!

IF YOU'RE [not] A KID:-) take care...this is a place where serious harm may result from misguided handling of products & information.

that's for damn sure

Reply to
--

I Exaggerated about the Parental Guidance,

NOTE: Aluminum is not as impervious to Magnetism as suggested, (is Always a Conductor) in fact it has a low reluctance to magnetism, but, at High [=83] DC Voltages & Currents it has an Electro/Physical ("Magnetic Flux") Effect of it's own ....I believe it's measured in Gauss as well. perhaps a bit off the charts.

Ever heard of the term: Ion Wind

Reply to
Roy Q.T.

in article snipped-for-privacy@storefull-3254.bay.webtv.net, Roy Q.T. at snipped-for-privacy@webtv.net wrote on 2/25/05 2:32 AM:

Whatever this post says is nonsense.

Bill

Reply to
Repeating Rifle

Bill: I hope you and your rifle have a good night tonight. won't you muzzle up to it & pull the trigger ..... ?

Where do you get off ? Are you a Physics Mayor or anything close to one ?

The post was an expansion on Aluminum, but, I happen to have one or two of those bobbind around "they" are crap.

Reply to
Roy Q.T.

in article snipped-for-privacy@storefull-3258.bay.webtv.net, Roy Q.T. at snipped-for-privacy@webtv.net wrote on 2/25/05 8:57 PM:

Just to be more specific, the sentence structure of your post was so awful, that nothing made sense. I could not get to the content.

Bill

Reply to
Repeating Rifle

Professor Bill: so'., you're a language & speech major, teacher, critic, online stalker ? which is it ?

If you think that's bad and illegible or void of mindful expression you haven't been around much., have you?

You must be stalking for someone to off or some secluded stuckup sheltered university dude that never gets out into the real world.

FYI; I got A's in English & Grammar all my life dude so bite the bullet., you want me to sound all snooty n grammatically correct don't ya. shiiiiiiiiiittttttt.....

gimme a break.

To end this: who cares anyway ?

Reply to
Roy Q.T.

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