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Message-ID: <009a01ca0591$50cba2c0$0900a8c0@AM>
From: "Alan Melia" <alan.melia@btinternet.com>
To: <rsgb_lf_group@blacksheep.org>
References: <E1MR4ck-00019O-GI@www14.emo.freenet-rz.de> <003501ca0554$292717a0$0900a8c0@AM> <B336A8E1DF4446438376D22996761106@lindavideo>
Date: Wed, 15 Jul 2009 21:59:44 +0100
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Subject: Re: Re: LF: Microwave oven transformers
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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 .
> >
> >
> >
> >
>
>