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Making a small transformer Answered

would you like to check this project out?
it needs a small transformer with 230v input, 12v output 100 to 150 mA. How much turn main and secondary do i need? it said that i have to reverse connected the transformer.

Sorry for asking, i'm not an electrical engineering student



For that project I believe they used s stalk 230 volt to 12 volt step down transformer and connected the circuit to the 12 volt output to drive the voltage up.

They used the secondary winding as the primary winding.

You are looking at a 20 to 1 transformer working at a 100% efficiency which never happens, so depending on the transformer core it will be more like 30 or 40 turns to one turn.

If your circuit is connected to a primary of 10 turns of 30 AWG the secondary will be 300 to 400 turns of 40 AWG.

You might find it easier to buy a cheep AC adapter from 230 to 12 volts open it up and take out the rectifier and connect the circuit to the 12 volt side of the transformer.

There is a lot to making a transformer like fish paper, resin, wire size to current not to mention core types like toroid or flyback.

I hope this helps.


Thank you for the fast reply sir...
is it different with AWG and SWG measurement?
is it affecting the transformers lifetime if i decreasing the wire size?
can i reuse a bobbin from CFL lamp? it's around 1 cm each side

i'll plan to makin it from scratch since i can't found it from local shop

sorry for my bad english
im curious of the transformer making you mention above :)

2014-06-02 22.09.51.jpg

Sorry for taking so long to get back to you.

Like Steve said AWG and SWG are different standards.

I have seen those inductor cores from CFLs they are small but you might be able to use it by wrapping the wire in the same way people do flybacks.

Keep the windings it has and add to the side ten turns I have done that and it worked.


it's a transformer... cuz it has 4 legs... sorry for a little details...
inductor just have 2 legs, isn't it?
correct me if im wrong.

should i wind the main layer of 12v first sir?
is there any tricky technique to test the output?

sorry too much ask... ill rate your answer, cuz u give me a looooot of details :)


Inductors of that type all have 4 to 6 legs check with a multi meter to be sure there is a wire between them.

Then take a wire and wrap it around on of the sides like I did on the transformer in this pic.

On one side I have the feed back coil 5 turns on the other I have the primary coil 10 turns.

Connect the output of your driver to the wires you added to the transformer and measure the output on the secondary with a meter.

You may need a capacitor and a diode on the output to get it up to full voltage so you can measure it.

Magnetic Wire 3.JPG

it's from another project board isn't it?

the key is just measure the output voltage right? so all i have to do is make the 40 to 400 turns of wire like you said before...

Its my first coil gun.

It kicks 3 volts up to 300.

If you want to kick 12 volts up to 240 volts, it is 10 turns on the primary, 400 turns on the secondary and that is at 50% efficiency on the transformer.


I think building a transformer from scratch, I mean, from like laminated iron and magnet wire, I think that would be very challenging even for someone who is an electrical engineering student.

If you cannot find this transformer from the usual places you buy parts from, it may be possible to salvage one from some inexpensive (preferably used or junk) piece of consumer electronics.

For example, I have seen a similar transformer inside a mains powered, LED alarm clock, like the one shown in this picture:


from Giovannire's fake-bomb alarm clock 'ible, here:


Anyway, if you happen to own one of those style of alarm clocks, it might be worthwhile to open it up, and carefully measure the AC voltage on the secondary side of that little transformer. I am expecting it to be around 12 volts AC.

By the way, the cost, physical size, and weight of a line frequency (50 or 60 Hz) transformer tend to scale with the amount of physical power the transformer can handle. In terms of power the "size" of the transformer you're looking for is about 2 watts, since

12V*0.15A = 1.8 W ~=2 W

In terms of physical size, a transformer like this will be about the same volume as the one in the disassembled alarm clock in the picture linked above, roughly a cube, about 3 cm on a side.

Thank you sir for the fast reply...
Yep, my local shop just have a 3A transformer...

i can found only 220v to 9v from a PC speakers
can i reuse the bobbin of this transformer?

it's around 1 cm each side, i found it in a CFL lamp...

btw i just plan to make this project

2014-06-02 22.09.51.jpg

I think the 220VAC to 9VAC transformer from the PC speakers might work as it is, no need to rewind it, for the homemade muscle stimulator you linked to at http://redcircuits.com/Page124.htm

I think the turns ratio on a 220VAC to 9VAC line frequency transformer is probably close enough (to that of a 220VAC to 12VAC transformer) for a project like this. You noticed in the notes for that circuit, the author suggests varying the input battery voltage as a way of varying the output voltage; i.e. lowering the battery supply voltage will lower the output voltage.

The little 1cm sized "transformer" from the CFL lamp might be an inductor. Examine it more closely. If it only has one winding, then it is just an inductor.

BTW, I thought I would mention: those tiny ferrite


transformer cores, like the one shown in the CFL in the attached picture, those are often held together by some very sturdy glue, so that it is difficult to take them apart without breaking them.

Immersing the transformer in boiling water, for about 10 minutes or so, is a trick that sometimes works to weaken the glue so the transformer core can come apart without breaking.