[ARC5] Slightly OT: Transformers

Thu Nov 28 18:04:07 EST 2013

Yes, it is certainly non-uniform but insulation of wire and windings is the
biggest problem.  Cu temp tells you more about that.   I didn't read about
this anywhere, just thunk it up.  Nice to know it is accepted practice.

Dennis AE6C

On Thu, Nov 28, 2013 at 9:16 AM, J. Forster <jfor at quikus.com> wrote:

> You certainly can use the Cu as a thermometer, but the temperature inside
> a transformer is non-uniform.
>
> -John
>
> ================
>
>
>
> > 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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> >> >> -----
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> >> 11/27/13
> >> >>
> >> >
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> >>
> >>
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