[ARC5] Slightly OT: Transformers

Thu Nov 28 13:30:45 EST 2013

  HA!  Dennis!
  You've been reading the text books!  This is the "official" way to
  measure temperature rise in a power transformer!
  It's ages since I've seen this method described.

  73 de Les Smith
  vk2bcu at operamail.com

On Fri, Nov 29, 2013, at 3:47, Dennis Monticelli wrote:
> It seems to me that one could measure the cold resistance of a winding
> (say
> the primary), then put the transformer under load, and then remove the
> load
> and take a fresh resistance reading right away.  The temp rise of the Cu
> is
> what you are trying to limit and that is easily calculated via the tempco
> of Cu which is about +0.39% per degree C.  The max temp rise of the
> winding
> should be kept below 150C.  This assumes the insulation is in decent
> shape
> and can handle 200C which modern transformer do.  You may wish to de-rate
> for old iron.
> 
> Dennis AE6C
> 
> 
> On Thu, Nov 28, 2013 at 8:19 AM, J. Forster <jfor at quikus.com> wrote:
> 
> > Steel quality sets max flux density.
> >
> > Circular mils is cross-section of copper in the windings, hence copper
> > loss.
> >
> > Generally transformers are designed so:\
> >
> > Copper loss = core loss.
> >
> > -John
> > =================
> >
> >
> >
> > > Ratings vary from 500 to 1000 circular mills per amp depending upon the
> > > quality of the steel used. The 500 rating goes back to the 30's and was
> > > repeated for decades in the ARRL Handbook but in WW2 and later in
> > consumer
> > > electronics materials improved.
> > >
> > > There was a posting somewhere of estimating the VA of a transformer by
> > > measuring the core but I cant find it right now.
> > >
> > > Carl
> > >
> > > ----- Original Message -----
> > > From: "Fuqua, Bill L" <wlfuqu00 at uky.edu>
> > > To: "Eric Mynes" <kc8wzb at gmail.com>; <ARC5 at mailman.qth.net>
> > > Sent: Wednesday, November 27, 2013 11:16 PM
> > > Subject: Re: [ARC5] Slightly OT: Transformers
> > >
> > >
> > >>  In the late 60's or 70's there was a multipage article in Electronics
> > >> Magazine on power  transformers
> > >> and how you can determine the rating of a transformer up to kW range.
> > >> The
> > >> magazine is gone now
> > >> but perhaps there is a URL that has the PDF of those magazines.
> > >> 73
> > >> Bill wa4lav
> > >>
> > >> ________________________________________
> > >> From: arc5-bounces at mailman.qth.net [arc5-bounces at mailman.qth.net] on
> > >> behalf of Eric Mynes [kc8wzb at gmail.com]
> > >> Sent: Wednesday, November 27, 2013 6:10 PM
> > >> To: ARC5 at mailman.qth.net
> > >> Subject: [ARC5] Slightly OT: Transformers
> > >>
> > >> Greetings all,
> > >>
> > >> I have some questions about transformers and this seems to be the only
> > >> group I'm in now that deals with tube rigs.  I hope you don't mind
> > >> elmering
> > >> me a bit by answering a few questions.  I mention slightly off topic
> > >> because one day (hopefully soon) I'll start building a power supply to
> > >> use
> > >> with my ARC 5 rigs, but for now, I just want to be able to power some
> > >> basic
> > >> homebrew tube transmitters.
> > >>
> > >> So, my questions go along the lines of...  I have several transformers
> > >> that
> > >> have followed me home from hamfests or someone has given me.  But most
> > >> are
> > >> not labeled in any fashion as to what they are rated for.  As stated
> > >> above,
> > >> I'd like to build a small power supply that can run some homebrew tube
> > >> rigs.  I might actually use some of the thousands of tubes that followed
> > >> me
> > >> home from hamfests instead of leaving them piled in boxes with no use.
> > >> I've tried googling any number or marking on the transformers trying to
> > >> find a manufacturer or specifications and haven't had any luck.  How can
> > >> I
> > >> test these safely as to not hurt myself or the transformer so that I
> > >> find
> > >> out at least the voltages I should expect out of them?  Right now, I'm
> > >> not
> > >> too concerned about finding how many amps they will provide as much as
> > >> now
> > >> much voltage is on the end of the wire.  The number of amps question
> > >> will
> > >> come soon though.
> > >>
> > >> Currently I have a transformer on my bench that has the following
> > >> markings
> > >> 110v004h82
> > >> 352052
> > >>
> > >> It appears to have 3 windings.  A black set (I presume is the primary),
> > >> a
> > >> red set with CT, and a green set with CT.
> > >>
> > >> I'm kind of skittish at just applying 110v to the black wires and seeing
> > >> what the others have for voltages.  So, I figure why not ask some hams
> > >> that
> > >> might have a better clue than me.
> > >>
> > >> Please respond to me off the list as I don't want to waste too much of
> > >> the
> > >> list's bandwidth on something that might be determined as an elementary
> > >> question that we all should know.  I'll be quick to say that I'm a very
> > >> much at an elementary stage on using HV and know enough to ask questions
> > >> before just trying things.
> > >>
> > >> Thank you for the bandwidth and Happy Thanksgiving to all
> > >>
> > >> 73,
> > >> Eric
> > >> k8ohz
> > >> ______________________________________________________________
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