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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.)

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    \$\begingroup\$ "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. \$\endgroup\$
    – Chris Stratton
    Commented Sep 10, 2020 at 3:01
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    \$\begingroup\$ @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? \$\endgroup\$
    – MicroservicesOnDDD
    Commented Sep 10, 2020 at 3:09
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    \$\begingroup\$ 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. \$\endgroup\$
    – Chris Stratton
    Commented Sep 10, 2020 at 3:11
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    \$\begingroup\$ 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... \$\endgroup\$
    – Chris Stratton
    Commented Sep 10, 2020 at 3:29
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    \$\begingroup\$ @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. \$\endgroup\$
    – Chris Stratton
    Commented Sep 14, 2020 at 10:34

2 Answers 2

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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.

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    \$\begingroup\$ Couldn't weight also be a factor? \$\endgroup\$
    – MicroservicesOnDDD
    Commented Sep 10, 2020 at 20:23
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    \$\begingroup\$ 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. \$\endgroup\$
    – Todd Wilcox
    Commented Sep 10, 2020 at 22:45
  • \$\begingroup\$ 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 \$\endgroup\$
    – teambob
    Commented Sep 11, 2020 at 10:51
  • \$\begingroup\$ @teambob Tell me that. I got by main circuit breaker destroyed by such a fire. So no more Al wires in my appt now. \$\endgroup\$
    – yo'
    Commented Sep 11, 2020 at 13:05
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    \$\begingroup\$ @manassehkatz-Moving2Codidact Magic admin edit allowed me to transmute Cu to Al so I have deleted your till then useful comment :-). \$\endgroup\$
    – Russell McMahon ♦
    Commented Sep 14, 2020 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.

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    \$\begingroup\$ 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. \$\endgroup\$
    – MicroservicesOnDDD
    Commented Sep 10, 2020 at 15:31
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    \$\begingroup\$ @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. \$\endgroup\$
    – Jon Custer
    Commented Sep 10, 2020 at 15:36
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    \$\begingroup\$ @MicroservicesOnDDD - there is a whole story concerning electrical wiring in houses. See 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. \$\endgroup\$
    – WhatRoughBeast
    Commented Sep 10, 2020 at 17:54
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    \$\begingroup\$ 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. \$\endgroup\$
    – Nate S.
    Commented Sep 10, 2020 at 18:52
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    \$\begingroup\$ @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? \$\endgroup\$
    – MicroservicesOnDDD
    Commented Sep 10, 2020 at 20:25

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