I need to know how and auto transformer works and how i can get 240 with it thanks in advance and if theres a website thats explains transformers that would be great (: thnx again !!
An autotransformer (sometimes called autoformer)[1] is an electrical transformer with only one winding. The winding has at least three electrical connection points called taps. The voltage source and the load are each connected to two taps. One tap at the end of the winding is a common connection to both circuits (source and load). Each tap corresponds to a different source or load voltage. In an autotransformer a portion of the same winding acts as part of both the primary and secondary winding. Operation he ratio of secondary to primary voltages is equal to the ratio of the number of turns of the winding they connect to. For example, connecting at the middle and bottom of the autotransformer will halve the voltage. Depending on the application, that portion of the winding used solely in the higher-voltage (lower current) portion may be wound with wire of a smaller gauge, though the entire winding is directly connected.
An auto transformer works like a regular transformer. It has one winding and therefore does not provide isolation, As a circuit it is an inductor with a fixed tap. If the applied voltage is across the outer terminals and the output taken from the tap than to one outer terminal it is a step down autotransformer. If the applied voltage is from the tap to an outer terminal with the output taken across the outer terminals then it is a step up auto transformer. You can get 240 volts from a 120 volt dual winding transformer by connecting the primaries in series and applying 120 volts to one winding and get 240 volts across both windings in series. Leave any secondaries unconnected. Remember this is not isolated so be careful as it is a shock hazard. If the output is zero then you need to reverse the connections to one winding. They must be connected so that the voltages add. The output current is the same as the normal primary current
Auto transformer is a single coil wound on a core(iron/ferrite) having three terminals. Out of three, two terminals are fixed on each side. But central terminal is provided in such a manner which can move on the coil from one side to another side. Voltage input is fed across two ends, and output is taken across central point and ground point. Accordingly one end/ common end/ becomes common to both input and output. In some cases, top (phase) terminal, winding is continued further to a tertiary point left open, and variable point moves up to this tertiary point then, in auto transformer only, step up of output is achieved. Please note that input and output voltages can not be isolated in auto transformer. However we same some money since same winding is used common to primary and secondary.
