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

[Geoff]

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
>
>
> --------------------------------------------------
> From: "Bill Cromwell" <wrcromwell at gmail.com>
> Sent: Sunday, December 09, 2012 8:11 PM
> To: <arc5 at mailman.qth.net>
> Subject: Re: [ARC5] Radio Shack transformers - was:Vibrator Power Supplies
>
>> Hi,
>>
>> I ran mine overnight on my BC-453 watching for some of the experimental
>> stations on 600 meters. That RS transformer only powers the tube
>> heaters.  It wasn't over heated but was running a shade less than a
>> quarter of it's "rated" load. It was warm enough I wouldn't want to load
>> it any further. A separate transformer provides B+. That other
>> transformer has an unused heater winding and was actually *cold* to the
>> touch. The garage is allowed to cool into the upper 50s overnight in the
>> Michigan winter. I'm glad this was pointed out. Now to start sprinkling
>> some bucking transformers around.
>>
>> 73,
>>
>> Bill  KU8H
>>
>>
>>
>>
>> On Sun, 2012-12-09 at 15:39 -0800, J. Forster wrote:
>>> I just measured the core loss of a Radio Shack 12.6V @ 2A transformer. 
>>> The
>>> unit is low loss to about 115 VAC, then rises rapidly:
>>>
>>> VAC      Power
>>>
>>> 090       2
>>> 100       2
>>> 110       3
>>> 120       4
>>> 130       6
>>> 138       8
>>>
>>> The instrument was a Sencore PR570 which analog multiplies V & I, so 
>>> it's
>>> real power, not reactive. This is virtually all core loss. Since the
>>> transformer is unloaded, the copper losses are small.
>>>
>>> -John
>>
>>
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>
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