12VAC to 24VAC transformer needed

I need to find a transformer (converter?) that will allow me to
upconvert from 12VAC to 24VAC in order to drive a small motorized
device (50 watts) for continuous duty. I tried using a 110V/220V
'travel' transformer -- it gave me the correct voltage but not enough
output current (probably not enough turns on the windings). I need a
transformer rather than an electronic converter since I am driving an
AC motor... isolation isn't an issue so I could go with an
Autotransformer. All of the transformers I see out there are for high
voltage primaries (110V or more). Thanks.

 

Thanks Larry -- seems like an obvious solution once you mentioned it
and MUCH better than finding a something special.

 

Hi Ed ... that was exactly the approach that I tried before (with the
'travel' transformer)... it just didn't give me enough current on the
output -- presumably it had a low number of turns. I think Larry
(above) gave me something to run with but thanks for the feedback!

 

[Chris]

Larry Brasfield wrote:

htewam@yahoo.com> wrote in message
news:1118691011.414013.202840@f14g2000cwb.googlegroups.com...
I need to find a transformer (converter?) that will allow me to
upconvert from 12VAC to 24VAC in order to drive a small motorized
device (50 watts) for continuous duty. I tried using a 110V/220V
'travel' transformer -- it gave me the correct voltage but not enough
output current (probably not enough turns on the windings). I need a
transformer rather than an electronic converter since I am driving an
AC motor... isolation isn't an issue so I could go with an
Autotransformer. All of the transformers I see out there are for high
voltage primaries (110V or more). Thanks.


The method I suggest below will require a slightly larger
transformer than one designed for your purpose, but it
would only leave about half the copper unused. For a
one-off application, that may be better than trying to
find an unusual transformer.

If you can find any transformer with a 24 VAC center-tapped
secondary rated for your load current (which appears to be a
bit above 2 A), then you can drive the center-tap and one end
with your 12 VAC and take 24 VAC from the ends. Be sure
to cover the primary lead ends as they will (likely) have a higher
voltage. This will function as an auto-transformer, with about
2 A flowing thru each half of the 24 V winding for a total of
4 A applied to the center-tap. If the center-tap is brought out
as a single wire, you need be sure it is good for 4 A. (If the
secondary is split, as is common, the wires should be large
enough for the rated current.)

--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.

Elegant. I like it.

But if the OP desires isolation, he might also want to get two
transformers of at least 70VA rating (12VAC * 6A or more secondary,
24VAC * 3A or more secondary) and backfeed the first transformer to
supply the second like this (view in fixed font or M$ Notepad):
`
` |
` T1 T2
` o------. ,-----|-----. ,-------o
` 12VAC In )|( )|( 24VAC Out
` )|( | )|(
` o------' '-----------' '-------o
` Sec. Pri. | Pri. Sec.
`
` |
`
` T1: Pri. 120VAC Sec. 12VAC 6A
`
` T2: Pri. 120VAC Sec. 24VAC 3A

created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

T1 is set up backward (the 12VAC is supplying the secondary of the
transformer, and the 120VAC primary is the output). This is called
backfeeding a transformer. The output of T1 is used to supply T2,
which outputs a standard 24VAC.

Good luck
Chris