[R-390] Bucking Transformer / Autotransformer Question
Bob kb8tq
kb8tq at n1k.org
Wed Jul 15 22:57:00 EDT 2020
Hi
There is *no* difference between a filament transformer wired this way or that
and an autotransformer …. none.
In both cases, if you are “dropping” voltage, the primary current back feeds the
line.
Bob
> On Jul 15, 2020, at 10:50 PM, Barry <n4buq at knology.net> wrote:
>
> As I replied to Roy just now, I'm thinking the autotransformer configuration may be the better way to go. I could get fancy and set it up with switches to that all of the tap combinations could be used for inputs and outputs to do both bucking and boosting with a few different values. Might be a fun project.
>
> Thanks,
> Barry - N4BUQ
>
> ----- Original Message -----
>> From: "Bob kb8tq" <kb8tq at n1k.org>
>> To: "Barry" <n4buq at knology.net>
>> Cc: "R-390 Forum" <r-390 at mailman.qth.net>
>> Sent: Wednesday, July 15, 2020 3:18:05 PM
>> Subject: Re: [R-390] Bucking Transformer / Autotransformer Question
>>
>> Hi
>>
>> The load current goes through the secondary. If you have a randomly chosen
>> 12V filament transformer, it likely
>> will do a fine job.
>>
>> The math:
>>
>> 10A load current
>> 10A secondary current (in the 12V winding)
>> 1A primary current (to feed 10A at a 10:1 ratio into the 12V winding)
>>
>> Obviously, 10A is a pretty big load ….
>>
>> Bob
>>
>>> On Jul 15, 2020, at 3:02 PM, Barry <n4buq at knology.net> wrote:
>>>
>>> I'd like to employ a bucking transformer for some of my equipment -
>>> particularly a Fluke 760A calibrator. I have a pretty hefty old
>>> transformer with two, separate 10V secondaries that can deliver 1.0A and
>>> 10.0A. It also has a tapped primary with taps at 115V, 120V, 126V, and
>>> 132V (I think I'm remembering all those correctly).
>>>
>>> I was thinking that since my mains voltage is right around 126V, then I
>>> could connect that to the mains and use the 115V tap in an autotransformer
>>> configuration. I'm unsure, though, whether that is the best way to do
>>> this and whether the primary windings will have to carry more current than
>>> it's capable of supplying.
>>>
>>> While I could connect one of the secondaries as a standard bucking
>>> configuration, I was thinking the autotransformer configuration might be
>>> better/simpler.
>>>
>>> Any thoughts on this approach? I'm just unsure of how much current that
>>> small section of primary would need to supply. I think it would be the
>>> total current drawn by the load but I might be thinking of that
>>> incorrectly so thought I'd ask.
>>>
>>> Thanks,
>>> Barry - N4BUQ
>>> ______________________________________________________________
>>> R-390 mailing list
>>> Home: http://mailman.qth.net/mailman/listinfo/r-390
>>> Help: http://mailman.qth.net/mmfaq.htm
>>> Post: mailto:R-390 at mailman.qth.net
>>>
>>> This list hosted by: http://www.qsl.net
>>> Please help support this email list: http://www.qsl.net/donate.html
>>
>>
More information about the R-390
mailing list