[ARC5] Slightly OT: Transformers

Peter Gottlieb hpnpilot at gmail.com
Thu Nov 28 14:16:24 EST 2013 

It's in common use for utility transformers, and indeed the standard. Note that it does not tell you any hot spot temperatures, more like an average. 


Peter

> On Nov 28, 2013, at 1:30 PM, Leslie Smith <vk2bcu at operamail.com> wrote:
> 
>  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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>>>>> 
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>>>> 
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