From Wikipedia, the free encyclopedia says: http://en.wikipedia.org/wiki/Isolation_transformer. Google for more information.
So maybe you should have one, but do not want to lay out the money for one ( they are surprisingly expensive ). This instructable describes one I built and gives you tips to build your own. With a bit of luck you can find a salvage transformer ( or 2 ) and put it together for cheap.
Step 1: Materials and Tools
- I used 2 identical old filament ( 6v ac ) transformers
- Case in my case a plastic card file.
- 120 volt wire, male and female plugs.
- Soldering iron
- Usual hand tools.
- 25.2VCT@ 2Amp $13 http://www.electronicsurplus.com/Item/127056/Triad_Magnetek%20-%20Transformer_%2025_2VCT_%202Amp_%20-%20F41X/
- Transformer. Dual 60V 200mA. $6 http://www.electronicsurplus.com/Item/134169/Vishay%20_%20Dale%20Electronics%20-%20Transformer_%20Dual%2060V%20200mA_%20-%20IPL-2329-11/
- Transformers. 20VAC 4Amps http://www.electronicsurplus.com/Item/8036/Unmarked%20-%20Transformers_%2020VAC%204Amps_%20-%2011-5-1558-55%20%20649-22/
- 115:12 VAC 6 AMP TRANSFORMER $7.50 http://www.surpluscenter.com/item.asp?item=15-1077&catname=electric
Step 2: Theory
There are a couple of ways of using more or less random transformers to make an isolation transformer. One way is to have 2 transformers with the same output voltage ( in my case 6 volts ) You can use one transformer to step the voltage down to 6 volts and the other transformer “backwards” to step the voltage up from 6 volts to 120. The transformers need not be identical they just need one voltage in common. Total power ( or really volt amps, VA ) should be limited to the lowest rating of any of the windings. This is how I first set up my isolation transformer.
A second way is to use a transformer rated for either 120 or 220 volts. Normally these have 2 completely separate primaries, you are expected to use them in parallel for 120 volts and in series for 220 volts. Instead use one as an input the other as an output. s makes a 1:1 transformer or an isolation transformer.
You might want to use a couple of microwave transformers to make you pair of transformers, just rewire to have equal low voltage sides. ( for higher power use as many secondary windings as will fit ). I would not keep the high voltage secondaries, I think this is too dangerous. The following instructable may help:
- How to: High current Microwave oven Transformer by HazzWold1993 https://www.instructables.com/id/How-to-High-current-Microwave-oven-Transformer/