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[OM] Re: [OT]Transformers (was Noisy T32 (wax potting))

Subject: [OM] Re: [OT]Transformers (was Noisy T32 (wax potting))
From: Joe Gwinn <joegwinn@xxxxxxxxxxx>
Date: Fri, 17 Oct 2003 13:50:51 -0400
At 3:17 PM +0000 10/17/03, olympus-digest wrote:
>Date: Fri, 17 Oct 2003 10:06:25 +0100
>From: "Julian Davies" <julian_davies@xxxxxxxxxxxxxx>
>Subject: [OM] Re: [OT]Transformers (was Noisy T32 (wax potting))
>
>The problem is the drilling, not the bolting. By putting a drill through a
>transformer, the laminations will be shorted and  eddy current will be
>increased.
>Transformers designed to be bolted have the laminations punched and deburred
>prior to being coated all over for insulation, then  assembled with the
>holes aligned to allow the bolt or rivet. The laminations stay insulated and
>the bolt does not contribute an eddy - current path of its own.

Yes, that's certainly how it's done in production.

In Moose's case, if I recall there was already a hole in the laminations, and 
all he had to do was to provide the bolt.

But for retrofitting a small power transformer, I wouldn't worry about a new 
hole or two, even if it does raise the loss slightly.  I suppose leaving space 
so the bolt can have a insulating sleeve would help, as then any connection 
would have to be via the burrs.

I would be far more worried about accidentally damaging the transformer while 
drilling, unless I could remove the core from the winding.  If the core is 
removable, then it ought to be possible to deburr the holes.  But this is a lot 
of work.

Anyway, this is why I preferred wax potting.  No disassemby needed, and wax 
won't hurt anything.

CH suggested using real electrical potting varnish, which would certainly work 
very well, but as he said it's hard to get these materials, at least in small 
quantities.  But CH does give me an idea -- ordinary shellac, available at 
paint stores everywhere, would work and again isn't going to hurt anything.  
Shellac can also be thin enough that it will simply soak into the transformer.  
Remove the shellac by soaking in alcohol.


>Julian
>
>Who got quite familiar with this designing and building valve amplifiers in
>a previous life.

Maybe it matters for an audio output amp, which has to handle a wideband (20 to 
20000 Hz) signal without distortion, but for a one-frequency power transformer 
it likely matters far less, so long as the power loss isn't excessive.

Valve amps are making a comeback in hi-fi circles (for the mellow tube sound) 
and never died for guitar amps (for a better grade of distortion), so a new 
career awaits you.

Joe Gwinn


>- ----- Original Message ----- 
>From: "Joe Gwinn" <joegwinn@xxxxxxxxxxx>
>To: <olympus@xxxxxxxxxxxxxxx>
>Sent: Thursday, October 16, 2003 2:41 AM
>Subject: Re: [OM] Noisy T32 (wax potting)
>
>
> > At 7:04 AM +0000 10/15/03, olympus-digest wrote:
> > >Date: Tue, 14 Oct 2003 15:41:05 -0500
> > >From: clintonr@xxxxxxxxxxxxxxxx
> > >Subject: Re: [OM] Noisy T32
> > >
> > Moose's report that in power transformers it's often the laminations, not
>the winding, that makes the noise is correct.  Bolting the laminations
>together is a standard practice, and will not cause a problem because the
>laminations are individually insulated.  In fact, many transformers are
>riveted together.


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