Alternating current (AC) is used in power transmission lines and in high-power devices, such as household appliances and lighting fixtures. Its characteristics make it ideal for long distance transmission and for the distribution of large quantities of electricity; it is used in devices that do not require a particularly controlled source of energy, such as devices for the generation of heat and light. Lower-powered appliances and other electrical devices, on the other hand, require a more controlled source of energy: direct current (DC). Since the household electricity supply is in the form of alternating current (AC), in many cases this must be converted to direct current (DC). Use the guidelines in this article to learn how to make an AC / DC converter.
Steps
Step 1. Choose a Transformer
A transformer consists of two magnetically coupled lead wire windings. One winding is called “primary”, and is powered by the main source of alternating current (AC). The other winding, called "secondary", will provide power to the AC / DC converter. The transformer, as well as the other components necessary for the realization of the AC / DC converter, are easily available in electronics or DIY stores.
- Size the windings. The power grid supplies 120 volts alternating voltage; if we converted it directly into direct voltage, we would obtain a much higher value than that required by household appliances and other electrical devices. For this purpose, the dimensions of the primary and secondary windings are suitably related so as to produce, on the secondary, an output voltage lower than the input voltage.
- Choose the secondary winding. The alternating voltage output from the secondary should be calibrated in order to have the same voltage as the direct voltage we want to obtain.
Step 2. Connect the primary winding to the main source of alternating current (AC)
The terminals of the transformer have no polarity, and can therefore be connected in any way.
Step 3. Connect the secondary winding to a full wave rectifier bridge
The transformer and rectifier terminals have no polarity, and can therefore be connected in any way.
- Build a full wave rectifier. It can be built with 4 rectifier diodes, rather than directly using a full wave rectifier device. These diodes are marked with the indication of the positive pole (cathode) and the negative one (anode). The four diodes must be connected in a ring: the cathode of diode 1 must be connected to the cathode of diode 2; the anode of diode 2 to the cathode of diode 3; the anode of diode 3 to the anode of diode 4; the cathode of diode 4 to the anode of diode 1.
- Connect the rectifier to the secondary winding of the transformer. The secondary winding should be connected to the cathodes of diodes 3 and 4; no polarity is required for these connections. The connection point between the cathodes of diodes 1 and 2 will represent the positive output terminal of the rectifier; the connection point between the anodes of diodes 3 and 4, the negative one.
Step 4. Connect a smoothing capacitor
Connect a polarized capacitor to the rectifier output terminals. The positive terminal of the capacitor must then be connected to the positive terminal of the regulator. This capacitor must be sized in such a way that its capacitance, in farads (F), is equal to (5 times the current that the AC / DC converter must deliver) divided (the secondary flow rate multiplied by 1, 4 times the frequency). The frequency may vary from country to country, but is typically 50 or 60 hertz (Hz).
Step 5. Add the final adjustment
Choose one of the voltage regulators available on the market, so that you can adjust the output voltage of the AC / DC converter to the desired value. The regulator is a device with 3 terminals: one common, one input connected to the smoothing capacitor, and one output. The latter will represent the output of the AC / DC converter.
