[ARC5] Transformer Ratings.

[Bob Groh]

My interpretation: the 30VA rating is applicable only to the 'whole
transformer' but with the proviso that 30 VA rating only applies to both
windings of each type.

i.e. each 12V windings by itself is only good for 1/2 of the total VA
rating, i.e. 15 VA / 12V = 1.25A each.
Put them in series (24V) and you can get 1.25A.  Put them in parallel and
you can get 2.5A (i.e. 1.25A per winding).

Ditto for the primaries - each primary is rated for 1/2 the total VA so 15
VA/115V or 0.13A

You can mix and match but you shouldn't exceed the current rating for any
one winding. I also think you would want to keep an eye on core current (I
am out on a limb here) but suppose you wanted to use one primary for the
input and the other primary as an output along with both secondaries. I
would probably be a bit conservative and split the 15VA rating of the input
among the 3 outputs.

To more explicitly answer your question: if you parallel both primaries and
drive with 115 VAC and parallel both 12V secondaries and use to drive your
rectifiers then the output current rating (of the transformer) would be
12VAC at 2.5A.  I think.

73
Bob Groh, WA2CKY


On Mon, Jan 10, 2022 at 7:29 AM David Stinson <arc5 at ix.netcom.com> wrote:

> A transformer with dual 12 V windings and dual 115 V windings
> rated at 30 VA.
> Am I correct in calculating that this transformer can source
> roughly 400 mills if used in a 12-Volt to B+ DC-DC converter circuit?
> Thanks.
>
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