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'[OT] XFORMER'
2002\11\04@102829 by techhead

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I have a transformer rated at 220 VAC primary, 24 VAC secondary @ 750
VA. I am looking for 12 VAC out so I will connect the 220 primary to 110
VAC and get the 12 output. I think I know the answer to this but wish to
avail myself of the experience and knowledge of others. I don't see
problems but was concerned with noise, heating, life expectancy etc. of
doing this.
I would appreciate some feedback.
Thank You.

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2002\11\04@114723 by Manu Nair

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Heating, noise and life expectancy would not be too much of an issue. The
issue would be the 750VA power rating which would be reduced to 375VA, if
you lower the voltages. In an ideal transformer, noise, heating and life
expectancy would be unaffected by lowering the voltages.

There is always some saturation that occurs at full rated voltage resulting
in some additional noise, heating and reduced life expectancy. But, for your
application, the transformer should exhibit lower noise, heat and show an
increase in life expectancy (because of the lowered stress), if you keep it
well below your new constraints. Hope this helps.

\manu

{Original Message removed}

2002\11\04@123201 by Mike Singer

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Techhead wrote:
> I have a transformer rated at 220 VAC primary, 24 VAC secondary @ 750
> VA. I am looking for 12 VAC out so I will connect the 220 primary to
110
> VAC and get the 12 output. I think I know the answer to this but wish
to
> avail myself of the experience and knowledge of others. I don't see
> problems but was concerned with noise, heating, life expectancy etc.
of
> doing this.

  Rewind the secondary, or find a new transformer.
  The sort of a garbage is scattered here, there and
everywhere

Mike.

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2002\11\04@144016 by Herbert Graf

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> I have a transformer rated at 220 VAC primary, 24 VAC secondary @ 750
> VA. I am looking for 12 VAC out so I will connect the 220 primary to 110
> VAC and get the 12 output. I think I know the answer to this but wish to
> avail myself of the experience and knowledge of others. I don't see
> problems but was concerned with noise, heating, life expectancy etc. of
> doing this.
> I would appreciate some feedback.

       Well, surprisingly, the issue isn't so much the voltage but the frequency.
A transformer is designed for a certain frequency and voltage, changing one
or the other may put you in a "bad" area of core saturation. However, if the
220V transformer is rated for 50Hz and you are feeding it 120V 60Hz that
danger is very remote, IMHO. TTYL

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2002\11\04@154446 by David Minkler

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I'm not sure how you are planning on using this transformer.  Is this a
one-up project or regular production?  What is the size of your load?

You should actually see improvements in noise (assuming you mean
mechanical noise from the transformer), heating and life expectancy.
Your load needs to draw no more current than the secondary was
originally rated for so, you will see a consequent reduction (to half)
of the original VA rating of the transformer (I'm assuming the
transformer is a single primary/single secondary type).  You should have
no problems with magnetic saturation (you are reducing the applied
volt-seconds).  The only real concern here is overtemping one of the
windings due to drawing too much current.

I'm not sure why Mike suggests you rewind the secondary.  While you
could regain the original VA rating by rewinding the transformer, you'd
have to rewind the primary as well.  If this is for a one-up and you
stay under 375VA you should be just fine.

Best regards,

Dave

Mike Singer wrote:
{Quote hidden}

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2002\11\04@163210 by techhead

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Rewinding the xformer is not an option. This is a one time hobbyist
application and the load is far under the rating. The xformer is one
that has been sitting on a shelf for years and this is more to get rid
of it than anything else. What I like, and why I ask the question is the
different views I get. Provides fuel for thought that may apply to
other, future projects. As for this project, (remote garage door
position indicator) it is getting a green light at this time, as I see
no serious objections. Still I thank everyone for their replies.

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2002\11\04@165320 by Mike Singer

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David Minkler wrote:
.
> I'm not sure why Mike suggests you rewind the secondary.  While you
> could regain the original VA rating by rewinding the transformer,
you'd
> have to rewind the primary as well...
.
> > Techhead wrote:
> > > I have a transformer rated at 220 VAC primary, 24 VAC secondary
> > > @ 750VA. I am looking for 12 VAC out so I will connect the 220
> > > primary to110 VAC and get the 12 output.

  Wisehead (Olin's copyright) :-) has 220 v transformer, he
didn't say he hadn't 220 v mains option. So I suggested
just to rewind secondary with thicker wire. For this kind of
the power it would be only few dozens of turns.

Best wishes,

Mike.

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2002\11\04@172202 by Mike Singer

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Techhead wrote:
> Rewinding the xformer is not an option. This is a one time hobbyist
> application and the load is far under the rating. The xformer is one
> that has been sitting on a shelf for years and this is more to get rid
> of it than anything else...

  The cheapest way is to throw it away and buy proper PSU,
PC AT for example for 10$.

 Mike.

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2002\11\04@184112 by Dwayne Reid

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At 09:26 AM 11/4/02 -0600, techhead wrote:
>I have a transformer rated at 220 VAC primary, 24 VAC secondary @ 750
>VA. I am looking for 12 VAC out so I will connect the 220 primary to 110
>VAC and get the 12 output. I think I know the answer to this but wish to
>avail myself of the experience and knowledge of others. I don't see
>problems but was concerned with noise, heating, life expectancy etc. of
>doing this.

The VA rating will decrease in direct proportion to the reduction in input
voltage.  As long as this is not a problem, go right ahead and use it.

Lets work some numbers.  24 Vac @ 750 VA is 31.25 Amps.  Output current is
limited by wire size, so it can't change.  If you change the primary
voltage such that you now have only 12 Vac at the output, max output
current is still 31.25 A which is 375 VA.

dwayne

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2002\11\04@195253 by David Minkler

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Ahhh

Mike Singer wrote:
{Quote hidden}

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