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RE: [TCML] primary tubing - now Aluminum wiring failures



Paul,

It is very common for MOTS to use aluminum wire, the reason is aluminum is
cheaper than copper and these transformers are not designed with any
regulation balance in mind, so copper losses and steel losses are never the
same and secondary losses usually do not equal primary losses, and that
reduces the regulation but it keeps the cost down. They are vacuum
impregnated with a varnish sometimes with a nitrogen push to keep the
moisture out of the layers, the common varnish being Y210, this is a
relatively lower cost varnish as compared to some varnishes, but it is a
common varnish in even the largest transformers, then they are baked in an
oven to cure out the varnish, that is where they get dark color from. The
magnet wire itself is also coated like normal copper magnet wire the coating
can vary depending on the application and desired thermal handling
capabilities. Most pole transformers also use aluminum windings using
aluminum foil for the low side, and others use all copper. 

--Brian

-----Original Message-----
From: Quarkster [mailto:quarkster@xxxxxxx] 
Sent: Friday, November 13, 2009 12:07 AM
To: Tesla Coil Mailing List
Subject: Re: [TCML] primary tubing - now Aluminum wiring failures

Paul -

I think the heavy gage aluminum wire used in your MOT primaries is just 
coated with a standard high-temperature magnet-wire insulation that happens 
to be a transparent golden-brown color.

MOTs are built to the OEM specifications of the oven manufacturers, so there

is probably no attempt "trick" anyone into thinking the primary wire is 
copper.

Regards,
Herr Zapp
----- Original Message ----- 
From: "Paul Brodie" <pbbrodie@xxxxxxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Thursday, November 12, 2009 10:54 AM
Subject: Re: [TCML] primary tubing - now Aluminum wiring failures


I recently discovered that the primaries in several of my MOT's are aluminum

wire with a copper colored insulation. Is this typical or unusual? I have 
noticed that all of the ones I have found with aluminum primary wire are 
newer ones. I find it rather humorous that they went to the trouble of using

copper colored insulation, evidently in an attempt to disguise the fact that

the primary wire is aluminum. The secondaries are all copper.

The way I found this out was when I disassembled a couple of MOT's and found

the primary windings were extremely light. I scraped a little bit of 
insulation off and low and behold, there's aluminum. I very carefully take 
the MOT's apart without damaging the windings. These windings come in handy 
for all sorts of experiments and tests. Of course, I also save the 
secondaries unharmed as well.

A really neat little trick is to take 3 secondary coils wired in series and 
loop several turns of 12AWG magnet wire through them. I then run this 
primary with one of my ignition coil driver circuits and it makes some nice 
arcs. I am considering disassembling a few more MOT's to see just how far I 
can go with wiring them in series this way with a common primary. I suppose 
it might help if I add some sort of core???

Anyone got any other ideas about ways to play around with these secondary 
and even the aluminum primary coils or any other suggestions?
Paul
Think Positive
  ----- Original Message ----- 
  From: jimlux
  To: Tesla Coil Mailing List
  Sent: Thursday, November 12, 2009 09:41
  Subject: Re: [TCML] primary tubing - now Aluminum wiring failures


  Quarkster wrote:
  > Jim -
  >
  > The terminations of the aluminum wire become oxidized, develop some
  > resistance across the termination, and eventually overheat.
  >
  > There are several contributing factors:
  > 1. Aluminum exposed to air immediately develops a high-resistance oxide
  > film;
  > 2. Aluminum wire is quite soft and "cold-flows" under pressure;
  > 3. Aluminum's high rate of thermal expansion can cause a
  > "self-degenerating" thermal-cycling problem where a small amount of
  > resistance creates localized heating, which causes the wire (and any
  > clamped connections) to expand. When the electrical load on that circuit
  > is removed, everything cools off, and if the aluminum has cold-flowed,
  > there is now less clamping pressure, which allows further oxidation in
  > the connection, which creates more resistance, which gets hotter the
  > next time the circuit is loaded, etc, etc.
  >
  > I've personally seen wire-nuts on aluminum wiring that got so hot that
  > the plastic wire-nut body completely melted away, leaving only the
  > conical steel spring from inside the wire-nut holding the wires 
together.
  >
  > Aluminum house wiring was a cost-saving measure that was implemented
  > without adequate testing, and turned out to be a complete disaster, a
  > great example of shoddy Engineering.
  >
  > Regards,
  > Herr Zapp



  It's a bit more complex than that, even.  Aluminum comes in dozens of
  different alloys, some more suitable than others for wiring.  Another
  aspect implicated in the house wiring issues is that about the same time
  that they started using aluminum wire as a cost savings measure, they
  also changed from brass to steel screw terminals on receptacles and
  switches. That aggravated the differential thermal expansion problem.

  There are modern aluminum wires that are perfectly safe, used with the
  correct terminations.

  As others have pointed out, most distribution transformers these days
  use aluminum wire.  My old Piper Cherokee 140 used aluminum wire (for
  weight saving).  There are miles of coaxial cable out there with
  aluminum shield.



   From a TC standpoint, I don't think aluminum buys you a whole lot.  On
  the primary, the difficulty in making a good adjustable tap point is
  probably a deal breaker, even if copper tubing costs as much as it does.
  On the secondary, it might be an OK trade, if you go up in size enough
  to account for the increased resistivity.  That will mean you get fewer
  turns per inch, so, for a given size coil you'll get fewer turns, so the
  inductance will be less, which will affect the tuning and the Lp/Ls ratio.

  I know several folks have made experiments of one kind or another, but I
  don't think they've spanned the necessary range of conditions to fully
  account for all the various factors;e.g. how do you disentangle the
  effect of changing the inductance in the seconday.. you'd need to wind
  one with aluminum wire, then wind another with (smaller) copper wire so
  the AC resistance is the same, but making sure the turns per inch makes
  the inductance come out right.  And for close wound coils (like a
  secondary), the AC resistance calculation is non trivial, because the
  fields from turns i-1 and i+1 affect the current distribution in turn i.
  (aka proximity effect).  That would change for the spacewound copper
  wire coil.

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