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

[jmfranke]

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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