Wiring your own... (mumble)... transformers

[AndrewT]

Hi,
I am too lazy to read the whole thread, so may have this already.

Buy a 15-0 +15-0 400VA transformer.
Strip off the outer insulation and add on extra turns to gives 18-0 then repeat for the other winding.
Re insulate.

 

[Christer]

Hi,
I am too lazy to read the whole thread, so may have this already.

So you missed it was started four years ago and that Lisandro has probably got a transformer long ago.

Don't worry, I also have a tendency to jump straight into threads sometimes.

 

[jamesjmcgee]

" Buy a 15-0 +15-0 400VA transformer. Strip off the outer insulation and add on extra turns to gives 18-0 then repeat for the other winding.

I know this is a real old thread but... How many turns to make 18v from a 15v transformer?

 

[AndrewT]

Hi,
start with a 230:15-0, 15-0 transformer.
Off load, it is about 230:16 giving a turns ratio of ~ 14.4:1
i.e. 14times as many turns on the primary as on each secondary.

If you want 18V loaded, the off load voltage will be ~19.2v. This requires a turns ratio ~ 12:1
To get this ratio you either have to increase the secondary turns number or decrease the primary turns number.

I do not recommend you touch the primary. Change the secondaries by adding turns.

If you want 220:18 or 240:18 these require a different turns ratio and you need to add the appropriate number of turns to get your target output voltage at your standard supply voltage.

As a start point do not strip any insulation.
Just wind 10 turns around the toroid core and measure the AC voltage from the ten turn winding.
Compare that to the off load voltage of the 15V winding. Now calculate the required turns to give your target output.

 

[unclejed613]

for a little bit of "thinking outside the box", here's a source of toroid cores you might not expect. it's a bit of work to get them ready to use, but they are BIG and they are usually FREE. get a deflection yoke from a large CRT TV, such as a 32". take the yoke off of the CRT. remove the wire. don't expect to re-use the wire, because the glue that holds it in place on the yoke tends to break enamel off of the wire, leaving areas of bare wire (unless you know someone who can re-enamel the wire...). once you get the yoke stripped down, the plastic frame should come apart easily. depending on the manufacturer, you will have a split toroid that clips together with steel spring clips (be very careful not to damage the brittle ferrite when removing these) or in some cases a single piece ferrite ring. while not exactly a nice shape for winding power transformers, it does function well, and looks, well. a little different (wow, a conical power transformer)...