[ARC5] Vibrator Power Supplies

[Leslie Smith]

An addition to Roy's experiment:  measure the primary current as the
primary winding voltage is increased.

(1) Set the subject transformer up with rated load and fed from a
variac.
     Plot primary winding current vs primary supply voltage.
    Estimate working voltage as 85% of the voltage where the current
    falls over the "knee" of the input I-V voltage.
    Alternately, estimate the point at which the I-V curve deviates from
    a linear response.

(2) Repeat, but w/out load.
 
Compare the loaded and unloaded results to estimate the value where
saturation begins.


  Les
  vk2bcu at operamail.com


On Sun, Dec 9, 2012, at 10:07, Roy Morgan wrote:
> 
> On Dec 7, 2012, at 8:50 PM, Geoff wrote:...
> > A lot of the old gear transformers are already starting saturation  
> > at 123 and are toast at 130. The use of bucking transformers to get  
> > down to 110-113 is very popular and the heat reduction is dramatic.
> 
> Geoff,
> 
> Thanks for your experience in the power supplies.  I often suggest  
> bucking transformers and sometimes note that you can run the primary  
> of it from either the line, or the reduced, bucked, output voltage.  I  
> had not realized that an older transformer from the junque boxe might  
> not do well running on the higher voltage line.
> 
> Experiment request to the group:
> 
> Find a recent Radio Shack small filament transformer  Run it at modern  
> line voltage and load it with a resistive load at or very near the  
> rating of the thing.  Look at the load voltage with a scope and see  
> how hot it gets in free air after an hour of running.  I've read that  
> they operate well into saturation with squared off voltage peaks, and  
> get quite hot.  This implies that the designers cut the iron used  
> below a happy amount,  and are counting on modern materials and  
> insulation to keep it running at least past the warrantee period. (IS  
> there a warrantee?  Maybe not.)
> 
> A search at http://www.radioshack.com
> returns NO hits for "filament transformer" but does list some  
> candidates for "transformer".
> They don't believe in filaments any more!
> The 12 volt offerings are:
> 
>   Model: 273-1352  |  Catalog #: 273-1352
> 
> 12.6V CT 1.2A Standard Center Tap Transformer with leadsPrice:$10.49
> 
> Model: 273-1511  |  Catalog #: 273-1511
> 
> 12.6V CT 3.0A Chassis-Mount Transformer with Leads
> 
>   Model: 273-1365  |  Catalog #: 273-1365
> 
> RadioShack® 12V CT 450mA Std Chassis-Mount Xformer w/ LeadsPrice:$7.49
> 
> 
> Model: 273-1385  |  Catalog #: 273-1385
> 
> 12.6V 300mA PCB-Mount Miniature TransformerPrice:$4.99
> 
> 
> 
> By the way this item:
> 
> RadioShack® Audio Output Transformer
> Model: EI-19  | Catalog #: 273-1380
> 
> Claims 1000 ohms primary, 8 ohms secondary and 300 to 10 khz  
> response.  Might do for command set use.  Price is $2.99  No power  
> level given.
> 
> Roy
> 
> Roy Morgan
> k1lky at earthlink.net
> K1LKY Since 1958 - Keep 'em Glowing!
> 
> 
> 
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