Building the transformer is quite easy.
Material needed:
Transformer (you have)
Magnet wire of the proper size for the amperage you desire
Insulating "paper", I have used tablet back and gasket material
Tape (I use self adhesive glass tape from MSC)
I also use insulating varnish again can be found at MSC
Tools
Hacksaw
Hammer
Punch
Big screwdriver
Drill(press) with a pretty good sized drill (say 1/2")
The process I use to make my transformers is as follow, as usual, YMMV or you may find a better way to do it.
!ABOVE ALL, WORK SAFELY AND BE CAREFULL!
Process:
Carefully saw off one side of the High Voltage winding and be sure NOT to knick the 110V or ~3V winding. Both of the lower voltage windings have always been wound together on all the transformers that I have messed with.
Now, I have found it easier to get the rest of the HV winding out by drilling into the center of the winding mass to make room to start pulling wires out. Some will wrap on the drill.
When you have a hole in the middle.
start pulling the wires out of the core (one side at a time). Remove ALL the wires and discard. When you get all the wires out, you can either remove the insulating paper or leave it for use on your new transformer winding.
When you have it all cleaned out, I usually use an air hose to be sure all the little chips etc are completely blown out of the clean core area as well as any that may have dropped into the 110/3V windings (you will keep these)
When every thing is clean, I usually put the core in a vice on the bench to hold it firmly. You now want to use your insulating paper to cover ALL exposed edges of the core. You don't want to knick the insulation on your magent wire or you will not have a good transformer (ask me how I know
After wraping the insulation on the core, I use glass tape to hold it in place. There are other tapes that can be used but this is my preference.
Measure the perimiter or the core to see how long a piece of wire it will take to make one turn and then multiply by the number of turns you think you will need. My experience is .9 to 1.0V per turn. Add a few feet of wire to this "estimate". For example, for the 40V AC that I just made, I used a piece of wire about 40ft long and only cut off a little bit at the end!
Start winding and be sure to leave a "tail" sticking out to connect to your circuit when done. Thread the wire through the core and carfully lay each winding next to the last one as best you can. When you fill that layer, I then wrap that winding with a layer of tape. Continue until you have what you think is the correct number of turns for the voltage wanted.
Now we are almost ready to test the actual voltage of the transformer.
BE CARFULL AS YOU WILL BE WORKING WITH POTENTIALLY LETHAL VOLTAGE/CURRENT!
REPEATING:
BE CARFULL AS YOU WILL BE WORKING WITH POTENTIALLY LETHAL VOLTAGE/CURRENT!
Scrape the ends of the wires that you have just wound and using an ohm meter, check to make sure you have continuity of the winding.
Also, check to make sure that you DO NOT HAVE continuity between the winding and the core. (In the former case, the transformer will not work, and in the second, you will see magic smoke in the following test
Set you volt meter to the appropriate scale and connect to the ends of the winding that you just made.
Using a FUSED power cord, hook it to the transformer and get ready to plug it in. Before plugging in, be sure there is nothing that will short out the windings of the transformer or anyone will get shocked.
BE CAREFULL AS YOU WILL BE WORKING WITH POTENTIALLY LETHAL VOLTAGE/CURRENT!
Now plug the power cord in the wall there should be a slight "chunk", but don't worry at this point. If things seem wrong, UNPLUG the cord immediately and find out why.
If all seems well, read the voltage on the meter. Is it the desired voltage that you want???
Hopefully yes, but if not; UNPLUG THE CORD and either add a winding or two or (?) to increase the voltage or remove a winding or (?) and test again.
Repeat as necessary until your voltage is correct.
If you have surplus wire, cut off the excess again leaving enough to allow you to connect to your circuit. I then spray the winding with my insulating varnish and let dry at least overnight before using the transformer.
Ok, now that you have the main winding for your servo, you may want to add another winding for say your 5V/12V controls and breakout board.
Repeat the above process as needed to wind additional winding(s) as necessary using the appropriate sized wire.
WIRE SIZING:
Based on what I have found, wire sizing is based on approximately 750 to 1000 CM per amp of current and having said that, I find that #14 does quite well on my setup of 3 servos each being fed by a gecko with a 5 amp fuse on it and haven't blown anything yet:})
If you work cleanly and carefully, you can make your own transformer this way and have the voltage(s) and current ratings that you want