Re: Re: LF: Microwave oven transformers

["Ken" <ken.h.wright@btinternet.com>]

Hi Everyone.
It looks as if I have really started something going, the main problem is 
obtaining the transformers, for too expensive to buy new. The obvious source 
are Council Tidy Tips, the problem there is that scrap microwave ovens come 
under the EU. WEEE directive, however some Tidy Tips are licensed to sell 
items like these, it is a matter of contacting various local authorities to 
find a licensed site, alternatively there is always Ebay.
KEN

73 de M0KHW



----- Original Message ----- 
From: "Alan Melia" <alan.melia@btinternet.com>
To: <rsgb_lf_group@blacksheep.org>
Sent: Wednesday, July 15, 2009 9:59 PM
Subject: Re: Re: LF: Microwave oven transformers


> 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
> 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 .
> > >
> > >
> > >
> > >