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I used to take TVs apart for fun (and parts, and learn.)

Some of the degaussing coils were beautiful -- nice, thick copper. Others were made out of aluminum wire. If I were engineering it, though, I would not have even thought of aluminum wire.

Can anybody shed some light on the thought process behind this? (You might relate how you have used aluminum wire in your product.)

I think "light" might sometimes be a reason (but probably not in the case for TVs with the big and heavy legacy CRTs).

I am after the engineering (or design) thought process here.

For those beginners or young ones who don't know, a degaussing coil is a coiled loop of wire, I'm guessing 40 to 75 turns (technically around an air core) held tightly together with electrical tape. The old cathode ray tubes would slowly get magnetized and exhibit a bit of "rainbow" or discoloration -- or if you had a child (like me) with magnets. ;-) The degaussing coil would remove the magnetization by a slowly decaying AC pulse.

Here are some sample pictures:

Example picture #1:

Degaussing Coil example pic 1

Example picture #2:

Degaussing Coil example pic 2

(I took everything apart because I wanted to learn how to make my own products some day.)

JRE
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MicroservicesOnDDD
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    "Why did they do X" doesn't really meet the criteria for *specific answerability* and is not a *design question*. One could *guess* things like cost or ability to hold its own shape, but SO sites aren't really meant to be about guessing. If you were *designing* a CRT and having *problems* with your degausing coil some aspect of those issues might be a fitting question. But you aren't. – Chris Stratton Sep 10 '20 at 03:01
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    Well, aluminum wire is cheaper than copper, that's the only reason I can think of to use it. It can cause other problems so it's not often used these day. – John D Sep 10 '20 at 03:03
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    @ChrisStratton -- I am interested in making my own inductors, perhaps integrating them in a product as part of the molded housing. Would aluminum make sense? How can I get answers without divulging inventions? – MicroservicesOnDDD Sep 10 '20 at 03:09
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    No, it would *not* make sense for most purposes in an inductor. If you can't ask a technical question without "divulging your invention" you probably don't have a sufficient knowledge of your problem to have invented anything, but if you're sure you do, find someone with suitable expertise, pay them to sign an NDA and help you. The free help on this site is reserved **only for problem for which you are willing to provide the necessary details** to make answerable. – Chris Stratton Sep 10 '20 at 03:11
  • @ChrisStratton -- I have made an air-core aluminum inductor that seemed to work surprisingly well -- and it was **so** light! – MicroservicesOnDDD Sep 10 '20 at 03:16
  • @MicroservicesOnDDD I've got an inductor that weighs less than yours – Chris Stratton Sep 10 '20 at 03:27
  • @ChrisStratton -- What is the minimum voltage that makes sense for using aluminum for an inductor in a boost converter? – MicroservicesOnDDD Sep 10 '20 at 03:28
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    What is the airspeed velocity of an unladen swallow? AFAIK, nobody uses aluminum in boost converters, at least none that you'd be mucking about with. But strange things have happened - the government once used bank-reserve silver in electromagnets, but there was a war on and the facility was going to be better guarded than any bank vault... – Chris Stratton Sep 10 '20 at 03:29
  • @ChrisStratton -- As I already said, I suspect that an increase in incoming voltage can help make up for the increased resistance and enable the decrease in cost. – MicroservicesOnDDD Sep 10 '20 at 03:44
  • In 1960, according to https://www.macrotrends.net/1476/copper-prices-historical-chart-data, Copper was between 27 and 31 US cents per US pound. The graph at https://en.wikipedia.org/wiki/History_of_aluminium#Mass_usage reads approximately $600 USD/metric ton or 28 US cents per US pound in 1960. So its not much of a cost saving either way. Comment because it didn't make a clear cut answer. – Criggie Sep 11 '20 at 00:49
  • Are you sure it's aluminum and not tinned copper? Have to ask... – Harper - Reinstate Monica Sep 11 '20 at 01:15
  • Aluminum is stiffer than copper. – Hot Licks Sep 11 '20 at 01:18
  • @ChrisStratton About 104mph max [apparently](https://wiki2.org/en/British_Aircraft_Swallow) - if you can still find one. – Russell McMahon Sep 14 '20 at 10:29
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    @Criggie to be meaningful you need to compare not the price per weight of Al and Cu but the price as a function of conductivity. Apparently that creates a factor of about two. – Chris Stratton Sep 14 '20 at 10:34
  • @Harper-ReinstateMonica -- Yes, it was definitely aluminum. Original source was a television demagnetization "loop", and was much, much, much too light to be anything else. I was making my own air-core Joule Thief coupled-inductors, and curious as to what would work, and how well. I had some surprising success, though I didn't really know what I was doing (and even after finally owning both the current, and the previous, versions of the Art of Electronics, there is still so much I don't know as a self-taught EE hobbyist.) – MicroservicesOnDDD Jan 16 '21 at 14:54

2 Answers2

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In consumer electronics there is only one reason.

Price

Saving 10c each on a run of 100,000 devices saves $10,000

the degausing coil doesn't need to be compact or have to low skin-effect losses so there's no compelling reason not to use aluminium.

Jasen Слава Україні
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    Couldn't weight also be a factor? – MicroservicesOnDDD Sep 10 '20 at 20:23
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    There was turbulence in the copper markets in the 1960s and early 1970s, which caused many home builders to use aluminum for home electrical wiring, which can be a problem and even a fire hazard in such homes that have not been renovated. Stands to reason that same copper market drove electronics manufacturers to substitute aluminum. – Todd Wilcox Sep 10 '20 at 22:45
  • Aluminium would be much more widely used if it wasn't for Aluminium's 35% higher thermal coefficient, which causes more loose connections and even fires. Aluminium is about 70% cheaper – teambob Sep 11 '20 at 10:51
  • @teambob Tell me that. I got by main circuit breaker destroyed by such a fire. So no more Al wires in my appt now. – yo' Sep 11 '20 at 13:05
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    @manassehkatz-Moving2Codidact Magic admin edit allowed me to transmute Cu to Al so I have deleted your till then useful comment :-). – Russell McMahon Sep 14 '20 at 10:21
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Reasons for using aluminium wire in a CRT degaussing harness:

  1. The lower electrical conductivity of aluminium (only 63% that of copper) would be good enough for the degaussing application.

  2. The lower density of aluminium (only 30% that of copper) would make the harness lighter and easy to handle.

  3. The lower weight combined with the lower cost of aluminium wire (only 40% that of copper) would result in a cost saving of 88%.

  4. The cost saving would be considerable even should the wire gauge be increased for increased rigidity.

vu2nan
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    Have you seen aluminum wire used anywhere else? I have seen it used in electrical transmission wire -- one additional benefit being that, from pole-to-pole, it requires less support, which I suppose means a thinner steel wire wrapped around it. But I don't think I've seen it in any other **products**. Thank you for your answer. – MicroservicesOnDDD Sep 10 '20 at 15:31
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    @MicroservicesOnDDD - my house has aluminum wiring, as did many built in the late 1960's through early 1980's. At the time it was cheaper than copper. – Jon Custer Sep 10 '20 at 15:36
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    @MicroservicesOnDDD - there is a whole story concerning electrical wiring in houses. See https://en.wikipedia.org/wiki/Aluminum_building_wiring It turns out that it's more difficult to make a long-term reliable connection with aluminum than with copper, and when the joint goes bad the connection heats up and can cause a fire. If you weren't around during the 70s, you missed a widespread scare when the issues were realized. – WhatRoughBeast Sep 10 '20 at 17:54
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    Anytime, @MicroservicesOnDDD! No, I've not come across aluminium wire used for electrical power wiring. But I have handled a length of unused 2-core 1.5 sq. mm aluminium cable. It's too soft to make a good connection. I have also come across 0.5 " coaxial hardline with a copper-sheathed solid aluminium core. The electrical transmission wire you have seen would be aluminium-clad steel wire. – vu2nan Sep 10 '20 at 18:20
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    @vu2nan, if I remember correctly, it was half-inch, large-strand, and the aluminum was actually polished on the outside. Could it have been lightning rod? I asked the service-man for a piece, which he gave, and now, if I can just find it, I can verify whether or not it's steel. – MicroservicesOnDDD Sep 10 '20 at 18:52
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    Automotive products sometimes make use of Copper Clad Aluminum (CCA). CCA gets you most of the cost and weight savings of aluminum while avoiding some of the problems terminating it. And since autos use 12V, the wires are thick, so you avoid the problems with thin aluminum wires. – Nate S. Sep 10 '20 at 18:52
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    Yes @MicroservicesOnDDD, the polishing would happen during extrusion. – vu2nan Sep 10 '20 at 19:11
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    Thanks for the information, Nate. – vu2nan Sep 10 '20 at 19:11
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    @vu2nan -- no, I mean **MIRROR** finish polished. That doesn't happen with stock extrusion. Wouldn't conduction according the skin-effect benefit from a straighter surface to travel upon, making it lower resistance? – MicroservicesOnDDD Sep 10 '20 at 20:25
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    @MicroservicesOnDDD, The mirror finish would be obtained by extruding the wire, submerged in oil. It would increase corrosion resistance. I am not too sure of it increasing the conductivity of the skin. – vu2nan Sep 11 '20 at 01:49
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    @MicroservicesOnDDD less support means it can span longer distances unsupported, so poles or pylons spaced further apart. by weight aluminium is stronger than steel, so adding steel would not help. – Jasen Слава Україні Sep 11 '20 at 02:18
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    @MicroservicesOnDDD I have seen aluminium windings in transformes, read also https://electronics.stackexchange.com/questions/19548/do-transformers-use-aluminium-windings – Arvo Sep 11 '20 at 10:12
  • @Jasen -- If what you are saying is true about aluminum being stronger than steel, then aluminum wire with a steel core would not exist. I think what you actually are referring to is that a particular alloy of aluminum is stronger than steel, and that the (different) electrical alloy they use is not of the same character, and is not stronger than steel, at least as far as tensile-strength. – MicroservicesOnDDD Sep 12 '20 at 22:10
  • steel is cheaper than aluminium, if steel was stronger than aluminium by weight they would make aircraft out of steel. – Jasen Слава Україні Sep 12 '20 at 23:46
  • @Jasen -- [This is what I'm talking about](http://aluminiumconductorcable.sell.everychina.com/p-108408911-bare-low-voltage-transmission-line-conductor-bare-aluminum-conductor-cable.html): "AACSR (Aluminum Alloy Conductor Steel Reinforced) has also a long service record because of its economy, dependability, and strength to weight ratio. The combined light weight and high conductivity of aluminum with strength of the steel cores enable higher tensions, less sag, and longer spans than any alternative as like as ACSR." – MicroservicesOnDDD Sep 13 '20 at 17:18
  • @Jasen -- [And this also (same page)](http://aluminiumconductorcable.sell.everychina.com/p-108408911-bare-low-voltage-transmission-line-conductor-bare-aluminum-conductor-cable.html): "AACSR conductors is widely used in power transmission lines of various rated voltage due to its simple structure, low cost and easy maintenance. Compared with 1350 aluminum conductor, 6201 aluminum alloy has higher tensile strength and corrosion resistance." Though I did not find the tensile-strength per weight ratio of either of these alloys compared to steel. – MicroservicesOnDDD Sep 13 '20 at 17:18
  • @Jasen -- Lightning hits planes all of the time. It is fortunate that aluminum is both light and very conductive. Steel planes probably would not do so well. – MicroservicesOnDDD Sep 13 '20 at 17:22
  • lightning hits automobiles too the seem mostly unharmed – Jasen Слава Україні Sep 13 '20 at 22:09
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    @MicroservicesOnDDD The Fisher& Paykel Smart Drive direct drive brushless washing machine motors (designed in NZ, avai;able in US, UK, ...) used copper wires in the stator coils. The whiteware division was sold to Haier. Sometime after that the coils were changed to Al. Which means that here in NZ you now find whole working motors in the curbside recycling instead of ones missing their copper coils :-). – Russell McMahon Sep 14 '20 at 10:26
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    Mitsubishi made some starter motors with aluminium windings - fortunately I had stashed some aluminium solder. – Jasen Слава Україні Mar 31 '23 at 03:44
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    @MicroservicesOnDDD Very late reply, but yes, the aluminum alloys that are good structural materials are abysmal as electrical conductors. For good conductivity, you need relatively pure aluminum, and pure aluminum is a very soft metal. – Hearth Mar 31 '23 at 04:04