Re: basics of transformer


"John Fields" <jfields@xxxxxxxxxxxxxxxxxxxxx> wrote in message
news:dr0tt1dlghf1goo1pejlbl12rsoeb2ulhc@xxxxxxxxxx
> On Mon, 30 Jan 2006 14:42:07 -0600, "Abstract Dissonance"
> <Abstract.Dissonance.hotmail.com> wrote:
>
>>I have a 40VCT .25A transformer and I'm wondering what those numbers
>>mean..
>>
>>does the 40VCT mean 40VAC from the center tap? If so across its full
>>secondary its 80VAC? and the .25A means that it can handle at most .25A
>>across its secondary coil(since its a step down from 120VAC the max
>>current
>>in its primary should be smaller... ~80/120*.25?).
>
> ---
> 40VCT means that with the rated voltage into the primary and the
> rated load on the secondary, the secondary voltage will be 40V
> across the entire secondary. (20V from the center tap to either
> end.)
> ---
>
>>Also should I assume these are all RMS values?
>
> ---
> Yes.
> ---
>
>> When I put my variac up to
>>100VAC and hook it up to my transformer I get about 40 volts across the
>>hole
>>secondary(hence 20V's across from the center tap). But this means that at
>>the mains(117VAC?) I'll be getting more than 40VAC across the full
>>secondary? Is this ok to have the transformer have a little more than its
>>voltage rating?
>
> ---
> Yes. It's supposed to because of the fact that since there will be
> resistive losses in the primary and secondary windings when the
> transformer's secondary is fully loaded, there will be an inevitable
> rise in voltage across the primary when it's less than fully loaded.
> The difference between the no-load and full load voltage is known as
> the regulation of the transformer, and for small transformers like
> you have is typically 30%
>
>
> --
> John Fields
> Professional Circuit Designer

cool...


Thanks a lot,
Jon


.

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