To: rsgb_lf_group@blacksheep.org
Date: Wed, 15 Jul 2009 17:28:38 -0400
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From: riese-k3djc@juno.com
Subject: Re: Re: LF: Microwave oven transformers
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On Wed, 15 Jul 2009 21:59:44 +0100 "Alan Melia"
<alan.melia@btinternet.com> writes:
> Hi Ken yes I appreciate the usage. I was a little concerned that if 
> the
> transformer was not designed for that kind of use it might not 
> necessarily
> have sufficent insulation from that end of the winding to ground to 
> survive
> the different stresses of of bridge rectifier. However Bob says he 
> has been
> using one like that for years so I guess they must have been 
> conservatively
> designed. I have had problems with transformers parallel primaries 
> and
> series secondaries ( a common way of getting high voltages for 
> valves ....in
> my youth :-))  ) breaking down under the voltage stress. I have 
> several
> transformers I salvaged from MOs and I now feel a lot happier about 
> their

I was able to mount a porcelain stand off at the same hole the ground lug
was mounted to ,, I think I then added a gob of clear silicon from the
local
hardware store,,, was surprised that it held up,, but it did

Bob K3DJC 


> use in HV PSUs. In the 50s.60s I was brought up with thick 
> insulation and
> porcelain standoffs :-))
> 
> An interesting thread.
> Best Wishes
> Alan G3NYK
> 
> ----- Original Message -----
> From: "Ken" <ken.h.wright@btinternet.com>
> To: <rsgb_lf_group@blacksheep.org>
> Sent: Wednesday, July 15, 2009 7:04 PM
> Subject: Re: Re: LF: Microwave oven transformers
> 
> 
> > Hi Alan.
> > The earthy end of the HV winding should be lifted from earth, and 
> a
> fullwave
> > bridge used .
> >
> > Ken
> > 73 de M0KHW
> > ----- Original Message -----
> > From: "Alan Melia" <alan.melia@btinternet.com>
> > To: <rsgb_lf_group@blacksheep.org>
> > Sent: Wednesday, July 15, 2009 2:57 PM
> > Subject: Re: Re: LF: Microwave oven transformers
> >
> >
> > > Hi all, I am very please to see not everyone sticks to a 12 volt 
> maximum
> > > supply voltage
> > > :-))
> > >
> > > One though that occurs to me is that if one side of the MO 
> transformer
> is
> > > grounded in oven service........one ought to check that the 
> winding as a
> > > whole is sufficiently well insulated from ground to stand 
> floating 2kV
> > > above
> > > ground. There may not be the same clearance /insulation on the 
> grounded
> > > end
> > > of the secondary as the intended high-voltage end?? On the other 
> hand it
> > > might be quite OK. I have a certain cynicism about "consumer 
> designs".
> > >
> > > Alan G3NYK
> > >
> > >
> > > ----- Original Message -----
> > > From: <dl4yhf@freenet.de>
> > > To: <rsgb_lf_group@blacksheep.org>
> > > Sent: Wednesday, July 15, 2009 2:34 PM
> > > Subject: Re: Re: LF: Microwave oven transformers
> > >
> > >
> > > These special transformers need the magnetic bypass because a 
> magnetron
> > > looks (as a load) like a Z diode.
> > > So they are powered, more or less, with a constant current 
> source rather
> > > than a constant voltage source.
> > >
> > > In other words, the "generator" (transformer) must have a large 
> source
> > > impedance, and that's what the magnetic bypass in the 'former 
> does.
> > >
> > > Cheers,
> > >  Wolf .
> > >
> > >
> > >
> > >
> >
> >
> 
> 
> 
> 
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