[ARC5] Slightly OT: Transformers

[J. Forster]

The 'rule of thumb' for transformer wire size is 500 circular mils/Amp.

-John

===================




>
> On Nov 27, 2013, at 6:10 PM, Eric Mynes <kc8wzb at gmail.com> wrote:
>>
>>
>> Currently I have a transformer on my bench ...
>> 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.
>
> Eric,
>
> The normal color code for transformers has been mentioned. I would expect
> yours to be:
> Blk - Blk  primary
> Red-CT-Red  high voltage
> Grn - CT - Grn  filament.
> With no Yellow secondary (usually rectifier filament) I would expect your
> unit is meant for use with solid state rectifiers.
>
> Here is a good web page that explains more:
> http://www.radioremembered.org/xfmr.htm
>
> A web search for “transformer color code” will bring many more.
>
>> I'm kind of skittish at just applying 110v to the black wires and seeing
>> what the others have for voltages.
>
> A very reasonable caution.  Another email suggests applying 12 volts (one
> tenth the likely primary voltage) to the black leads to see what the other
> winding voltages are.  This is a very good technique.  If you have a
> variac and a 12 volt transformer available, it makes even more sense -
> start at zero with the voltmeter attached to a secondary and see what
> happens.  The posted advice of using a light bulb, and not connecting your
> meter before switch-on is good.
>
>> ... don't want to waste too much of the list's bandwidth on something
>> that might be determined as an elementary
>> question
>
> This is a very fine question and well worth our time on the list. Asking
> questions before trying things will keep you safe, informed, and learning!
>
> The table at the website:
> http://wb0nni.dakotamade.com/xfmrpwr.html
> Is very useful.  (the left most power column should be 0.1 not 1.) The
> abbreviation IVS (Intermittent Voice Service) is likely equivalent to the
> term ICAS (Intermittent commercial and amateur service) used in tube
> ratings.
>
> The ARRL Handbooks of a long time ago offered a graph version of this
> table, plotting power rating vs. cross section core area.  Either will get
> you started.  (Count the power used in all secondaries.)  For filament
> windings that bring the actual winding wire out for connection, you can
> estimate current rating by wire size.  I think this is done less seldom
> than it used to be: modern transformers seem to use all flexible leads.
>
> I have not seen advice or tables that make a correction for potted
> transformers.  Oil filled military transformers are rare, but we do
> sometimes find steel cased, tar-filled commercial transformers.  I suggest
> using a number from the table, and under-loading the transformer you have
> by a modest amount.
>
> Having a collection of transformer company catalogs is very useful.
> www.bunkerofdoom has many such catalogs.
>
> You’ll have a success with all the advice from the list, I’m sure.
>
> Roy
>
>
> Roy Morgan
> RoyMorgan at alum.mit.edu
> K1LKY Since 1958
>
> ______________________________________________________________
> ARC5 mailing list
> Home: http://mailman.qth.net/mailman/listinfo/arc5
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:ARC5 at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>
>