[ARC5] Radio Shack transformers - was:Vibrator Power Supplies

[WA5CAB at cs.com]

It should probably be noted that the effective buck voltage (the amount 
that the voltage to the load is reduced) is (for the same buck/boost 
transformer) slightly less with the auto-transformer connection than it would be with 
the secondary connected in series with the load (standard buck connection).  
As an unrealistic but easy to understand example, if the primary has 100 
turns and the secondary 10 turns, with the secondary connected in series with 
the load, the reduction would be 10/100 or 10%.  With the secondary 
connected in series aiding with the primary (autotransformer connection), the 
reduction will be 100/110 or about 9.09%.

In a message dated 12/09/2012 22:39:59 PM Central Standard Time, 
geoffrey at jeremy.mv.com writes: 
> There was a study done a few years ago on another forum using the various 
> 
> possible configurations. It was determined, for a quality transformer at 
> least, that the autotransformer configuration is the most efficient by a 
> hair. There were some caveats which I dont remember and I'll see if I can 
> find the info.
> 
> 
> ----- Original Message ----- 
> From: "jmfranke" <jmfranke at cox.net>
> To: <wrcromwell at gmail.com>; <arc5 at mailman.qth.net>
> Sent: Sunday, December 09, 2012 8:24 PM
> Subject: Re: [ARC5] Radio Shack transformers - was:Vibrator Power Supplies
> 
> 
> >For this same reason, for reducing voltage it is better to put the 
> bucking 
> >transformer secondary in series with the bucking transformer primary. The 
> 
> >phasing of the secondary is selected to reduce the voltage across the 
> >primary. What is being done is the secondary winding is being added to 
> the 
> >turns in the primary winding. The supply neutral is connected the free 
> end 
> >of the primary and the supply line is connected to the free end of the 
> >secondary. The output neutral is connected to the input neutral and the 
> >output line is connected to the tap between the primary and secondary. 
> The 
> >reduces the voltage across the primary which reduces the transformer 
> >losses. Too many transformers are designed with the input voltage getting 
> 
> >close to core saturation and the method suggested in the BAMA article 
> puts 
> >the higher line voltage across the primary, which pushes the bucking 
> >transformer even closer to saturation.
> >
> >John  WA4WDL
> 

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