I had physics only in high school, with your help; I hope I could
modify the transformer and utilize the vanity lights I bought oversea
years ago. Those lights come with a simple transformer that is
supposed to convert 220v to 12v. When the input power is 110v here,
the output is only 6v and lights are too dim for its function. It's
not cost efficient to buy a new transformer for each of light. So, I
am trying to modify the transformer. When I used only 1/2 of original
length of magnetic wire, the output voltage was decreased by half.
However, when I double the length of magnetic wiring, the output
voltage did not increase, but kept at a constant 6v. When I measured
the voltage between the light and VT1 or R2 (see picture 1,
http://necklace4all.ecrater.com/product.php?pid=2159832), I got my
desired voltage 12v. Should R2 be removed and replace a wire at the
red marks shown in the picture 2 (click to enlarge the photo)? Any
suggestions in plain English will be deeply appreciated. Thanks all
in advance.

Christina

On Mon, 10 Mar 2008 08:29:37 -0700, song.yc wrote:

> I had physics only in high school, with your help; I hope I could modify
> the transformer and utilize the vanity lights I bought oversea years
> ago. Those lights come with a simple transformer that is supposed to
> convert 220v to 12v. When the input power is 110v here, the output is
> only 6v and lights are too dim for its function. It's not cost
> efficient to buy a new transformer for each of light. So, I am trying
> to modify the transformer. When I used only 1/2 of original length of
> magnetic wire, the output voltage was decreased by half. However, when I
> double the length of magnetic wiring, the output voltage did not
> increase, but kept at a constant 6v. When I measured the voltage
> between the light and VT1 or R2 (see picture 1,
> http://necklace4all.ecrater.com/product.php?pid=2159832), I got my
> desired voltage 12v. Should R2 be removed and replace a wire at the red
> marks shown in the picture 2 (click to enlarge the photo)? Any
> suggestions in plain English will be deeply appreciated. Thanks all in
> advance.
>
> Christina

What sort of bulbs does the vanity have? The picture you give is of a
power supply with a rectifier that would provide DC, and possibly some
voltage regulation (I suspect that the "VT" parts are surge protection,
but I try not to underestimate the oddity of someone else's nomenclature).

Most of the 12V halogen lamps that I have had die on me have perfectly
good transformers -- it always seems to be the socket or the wiring in
the head that gives up the ghost. If the bulbs will run off of 12V AC,
then poll your friends -- if they have a dead halogen fixture chances are
you can use the transformer from that.

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html

On Mar 10, 8:29=A0am, song...@gmail.com wrote:
> I had physics only in high school, with your help; I hope I could
> modify the transformer and utilize the vanity lights I bought oversea
> years ago. =A0Those lights come with a simple transformer that is
> supposed to convert 220v to 12v.

Three solutions are feasible. One is to rewire the transformer (this
may be provided for, the internal wiring might be two windings
that can be series-connected for 220v, or parallel-connected for
110V). A second, is to connect to 220V (it's not the common plug,
but US houses do have 220V for water heaters, stoves, etc.).
Third, one can replace the transformer (120V transformers of
this type are used for lawn lighting, and for similar vanity lights),

It'll take a technician to rewire the transformer, an electrical
contractor
or similarly competent individual to make up a suitable wall plug
connection, but replacing the transformer is just a matter of ... some
money. Count up the lamps, and calculate the power and/or
current requirement, before you go shopping.

There's another variant, the so-called autotransformer, which provides
a 220V output and plugs into a 110V socket. It's a little more
expensive,
but it solves the 220V problem for ALL your electric appliances,
up to the unit's power limit.

Thanks Tim and Whit for your suggestions. I have over 10 of those
lights. It may not be cost efficient to get all new transformers.
Also, it's not easy to get 220v in all the bathrooms. So I am still
thinking diy of transformer modification.
I did put a radio together from a IC board back in high school and
enjoyed work then very much. So, I hope I can do it now.
As Tim pointed out that Part "VT" are regulators. I could pinpoint at
one of them and give me desired voltage as the meter indicated. I
just was not sure how to rewire the transformer to bypass one of
regulator and its sub-group parts. Do you think if I remove R2 and
connect two red dots shown in photo2, http://necklace4all.ecrater.com/product.php?pid=2159832,
will it work? Thanks again!

Christina

Ed, thanks for your help.

The red wires go to the power line.

I measured from the red dot to the big solder blob near C1. It gave
reading around 60 volts; I have to set the meter at 250 volts to read.

I could find any print or label for VT1 and VT2. Those transformers
are not made in US. I opened several transformers from different
lights. None of them give any label. But VT1 and VT2 look like
regulator with three legs.

Christina

On Mar 11, 4:29=A0am, song...@gmail.com wrote:
> I had physics only in high school, with your help; I hope I could
> modify the transformer and utilize the vanity lights I bought oversea
> years ago. =A0Those lights come with a simple transformer that is
> supposed to convert 220v to 12v. =A0When the input power is 110v here,
> the output is only 6v and lights are too dim for its function. =A0 It's
> not cost efficient to buy a new transformer for each of light. =A0So, I
> am trying to modify the transformer. =A0When I used only 1/2 of original
> length of magnetic wire, the output voltage was decreased by half.
> However, when I double the length of magnetic wiring, the output
> voltage did not increase, but kept at a constant 6v. =A0When I measured
> the voltage between the light and VT1 or R2 (see picture 1,http://necklace=
4all.ecrater.com/product.php?pid=3D2159832), I got my
> desired voltage 12v. =A0Should R2 be removed and replace a wire at the
> red marks shown in the picture 2 (click to enlarge the photo)? =A0Any
> suggestions in plain English will be deeply appreciated. =A0Thanks all
> in advance.
>


That does not look like a simple transformer power supply to me. Are
these lights dimmable or something? Anyway, to change the output you
need to halve the number of turns in the primary, not double the
secondary as you need to get 2x more current flowing in primary
turns. But, is it worth it for your time, 12V halogen transformers
are really inexpensive.

Cheers

On Mar 11, 4:29=A0am, song...@gmail.com wrote:
> I had physics only in high school, with your help; I hope I could
> modify the transformer and utilize the vanity lights I bought oversea
> years ago. =A0Those lights come with a simple transformer that is
> supposed to convert 220v to 12v. =A0When the input power is 110v here,
> the output is only 6v and lights are too dim for its function. =A0 It's
> not cost efficient to buy a new transformer for each of light. =A0So, I
> am trying to modify the transformer. =A0When I used only 1/2 of original
> length of magnetic wire, the output voltage was decreased by half.
> However, when I double the length of magnetic wiring, the output
> voltage did not increase, but kept at a constant 6v. =A0When I measured
> the voltage between the light and VT1 or R2 (see picture 1,http://necklace=
4all.ecrater.com/product.php?pid=3D2159832), I got my
> desired voltage 12v. =A0Should R2 be removed and replace a wire at the
> red marks shown in the picture 2 (click to enlarge the photo)? =A0Any
> suggestions in plain English will be deeply appreciated. =A0Thanks all
> in advance.
>

That does not look like a simple transformer power supply to me. More
like some sort of switching power supply? What is VT1 and 2 and that
small ring ?transformer doing?
But anyway if it were a simple transformer, to change the output you
need to halve the number of turns in the primary, not double the
secondary as you need to get 2x more current flowing in primary
turns.
If it's a swichmode supply it may be altered by changing the duty cyle
but I doubt you'd double it. You would then need to also alter the hf
transfomer winding ratio. You'd need an oscilloscope to work out where
to make the change(s). If this does not sound too simple and it's not,
switchmode supplies can be tricky to get right (and reliable).
If you can I'd just throw the PS away and buy a cheap halogen power
supply they can can be got for ~$6 look on ebay.

Cheers

Hello Ed and PLOSSL,

It is more complicated than I can handle. I am giving up on changing
the output voltage now. It is better to find a right transformer or
halogen power supply. Thanks you all for your help!

Christina