Seeking help for layman: Double the output voltage in a simple transformer

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

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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,

will it work? Thanks again!

Christina

Do the red wires go to the lights?

Very carefully, with your meter set to AC and 20 volts or higher, measure from the large red dot to the big solder blob near C1. What do you get?

VT1 and VT2 should have something printed on them, on one side or the other. Can you see what is printed on them and post it?

Ed

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

So the white wires go to the lights?

VT1 & VT2 could also be transistors, or SCRs or triacs.

Do you know the specs on the lights? How many are in the string, and what current they need?

Ed

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

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