I have a DC adapter that requires a 220V 50/60 Hz input, and it has a 3.2 V, 1500mA output. If I have access to a 110 V system, what are the potential issues with taking a soft iron core, winding an (insulated)primary wire around it with 10 loops and a secondary with 20 loops, and using this to transform the 110 V input into a 220 V input? It should be possible and safe because of the low wattage involved right? What would be the best way to do this without buying a transformer?
Disclaimer: I have no intention of actually doing this.
Safety issues ?
Well the windings may have a maximum voltage rating… they may have been made for turning 110 into 55 , or something else lower… not higher.
Sometimes the primary winding gets hot even with no load…eg it wasn’t a design tested for 110 to 220 use. Something to do with resonance ? and a capacitor changes the resonant frequency away from the mains frequency ?
You’d have to make sure the wire you are using is rated for the voltage/current required. Albeit, 3.2V at 1.5A is a whopping 4.8Watts. The 110 and 220 voltage do exist. Also, it would be horribly inefficient unless you can get real nice and tight and even windings.
Is this 3.2V AC or DC?
3.2V DC. How inefficient could it be? And would it matter? As you note, it’s just a 5 W output.
Well yea, you could wind your own transformer. But why would you? I could certainly see doing it for educational purposes. But for a permanent application, I would never recommend someone wind their own power transformer if one can be purchased. A COTS transformer will meet certain safety and efficiency standards, whereas your homebrew transformer will not.
Furthermore, if I had an AC-to-DC adapter that required a 240 VAC input, and my power source was 120 VAC, my solution would not be to use a step-up transformer. My solution would be to simply buy an adapter that required 120 VAC input. They’re pretty cheap, ya know.
For the sake of science : I did try to do exactly the same thing in high school (220v to 110v with 10 turns of wire on the secondary and 20 …). The result was a big flash and the fuse blew off.
On investigating, I realized that the wires you use must be able to at least stand the current produced even if you consider it as a pure impedance. So in reality a 110v to 220v transformer (5w rated) will have a few hundred turns of wire in the primary and double that in the secondary - so that amperes drawn are not too high (when the secondary is open) and there is not a heat problem.
As to your 3.2 V adaptor : there’s a good chance that it will work with 110v since it maybe a SCR type and not transformer based. Have you checked ?
The basic idea is OK, but there are a number of issues with the realisation.
You can’t do this with only 10 or 20 turns. Whilst the turns ratio is OK, you are not creating a device with enough inductance to prevent the primary turns from looking mostly like a dead short.
Another way of looking at is that a transformer is an impedance transforming device. In a perfect device if you have an infinite impedance on the output (ie nothing is connected) the input should also look like an infinite impedance - and no current should flow in the primary either. When the output has a load attached, the reflected impedance on the input allows current to flow in the primary. The trick is that you need to couple the primary and secondary together magnetically with enough efficiency to make this happen. This is the mutual inductance. 10 turns isn’t going to do it. Not at 50 or 60 Hz. This is why mains transformers have hundreds of turns.
Also, a proper mains transformer is wound so that the mains windings are totally separated from the secondary windings. This is partly to avoid bad things if there is a serious failure (many thousands of volts breakdown are usually required), and also to reduce the inter-winding capacitance - which has a habit of coupling common node noise from dirty mains into the output.
yeah you need lots of wire in a coil to provide impedance and a field.
It is possible to make your own transformer. Using a laminated core instead of a solid soft iron core is a lot better. With a solid core you lose a lot of energy to eddy currents induced in the core. A laminated core is much more efficient.
As others said, you need a LOT more turns of wire. The easiest way to do this is to create a jig to help you automatically wind the wire. You can do it by hand, but it’s a royal pain in the butt to do so. You need to make a lot of turns and you need to make the coils neat with the wires packed nicely together. It’s extremely tedious to do by hand.
Personally, given the cost of an off the shelf 110/220 transformer, I don’t think it’s worth the effort to wind your own, though it is fun to do once in your life just for the learning experience.
ETA: Also, make sure your wire insulation is sufficient. Remember, 220 volts AC is not 220 volts peak to peak, that’s RMS. The peak voltage is up around 311 volts. Allow for a bit of a safety factor as well.