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Subject: Re: welding a transformer core
X-Newsreader: Microsoft Outlook Express 5.50.4807.1700
Date: Mon, 16 Dec 2002 23:22:36 GMT
NNTP-Posting-Date: Mon, 16 Dec 2002 18:22:36 EST
Organization: Magma Communications Ltd.
"John Crighton" wrote in message
> On 16 Dec 2002 01:50:17 -0800, email@example.com (Viktor
> Mikhailovich Polesov) wrote:
> >I milled out the welds of a salvaged microwave oven transformer to
> >disassemble the core to get the secondary wiring out, in order to
> >rewire it with a heavy gauge wire. This is a laminate core
> >transformer, with the core made of many small sheets of what appears
> >to be laminated stainless steel stacked and welded together. I
> >suppose if I had been more stubborn I could have gotten the secondary
> >out without disassembling the core, but I'm impatient. Even still it
> >was a huge pain and even after disassembling the core, I still had to
> >resort to hack-sawing the secondary wiring.
> >So now I have a transformer core that I need to weld back together.
> >Can anyone say for certain if stainless is commonly used here, and if
> >so should I use MIG or TIG to put it back together? Heat dissipation
> >while welding is a concern, because I used insulated wiring in the new
> >secordary as opposed to enameled wire. I don't want to melt the
> >insulation during the welding. I suppose I would be better off with
> >TIG in this regard, no?
> >I'm working on making a spot welder of the sort described here:
> >The owner of this web page does not discuss inductive effects. Aren't
> >you in danger of frying the primary-side SCR without some provisions
> >in this area?
> Hello Viktor,
> I note what you say about disassembling being a pain, I found
> that too initially but now I can disassemble a transformer like
> this one fairly quickly.
> I use a band saw to make about a 1mm deep cut along each weld.
> Using a stone mason's or bricklayer's chisel called a bolster which
> has a blade about 4" (100mm) wide, I split the joint. There is
> usually enough of the original weld on both the "E" and the "I"
> to hold the laminations together.
> Like you, I also hacksawed the secondary winding but now
> I use two pieces of 2" by 2'' by 1/8" angle iron to support
> the secondary winding. Then use a wooden block and a
> hammer to knock the core and loosen the complete
> secondary winding away from the core.
> I have used the Mig and Tig to weld the "I" piece back
> to "E" piece but now I like to tack weld little "L" shaped
> brackets to both the "I" and "E" sections so that they
> can be screwed/ bolted together. I have been making
> chokes recently and it is nice to have the ability to adjust
> the gap between the "I" and "E". Makes the core nicer
> to use for future experimenting.
> The laminations are not stainless steel but a special
> type of steel made for transformer use. There are various
> grades of this special steel and microwave oven transformer
> cores are low grade, I was told by a transformer expert.
> Anyway, I found that ordinary MIG and TIG wire were fine
> for welding the laminations of the core.
> That particular spot welder project interests me also. I have
> been on the look out for some suitable electrode material
> at the scrap yard. No luck yet.
> Since I would be using SCR's or semiconductor relay from
> the scrap yard, probably many times more robust than needed
> at a cheap price, I would not be worried about them.
> Good luck with your project. Let us know how you get on.
> John Crighton
I noticed your "making chokes" comment. I used 2 microwave transformer cores
to make chokes/inductors/reactors for my AC to DC converter for my Miller
buzzbox. Looking for any hints on tuning the gap between the Es and Is for
max inductance without saturation. Can you help?
PS It's a good thing these microwave transformers are cheaply made and the
Es and Is are not alternated as in a good transformer!
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