[ARC5] Slightly OT: Transformers

J. Forster jfor at quikus.com
Thu Nov 28 12:16:22 EST 2013 

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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