The Power transformer
my Example is
the Primary is 220 volts (Philippines Base) but you can Deduce it by Dividing by 2.
the Secondary is 12-0-12volts or 0-12volts
we are going to compute specifies 12 volts output with 750ma current (my Example) converting milliamperes to ampere will give us. .75a , multiplying voltage by current gives us wattage or power.
12x.75 = 9 watts
after having solved for the wattage of the transformer, which is 9 watts, look at Tables 1, where 9 watts is listed, follow the table horizontally and pick up the date for the center leg, thickness and turns per volt.
Center leg - 3/4
thickness - 3/4
turns per volt - 10
see at Table 1 and Table 2
the nest step is to compute for the number of turns for the the primary and secondary coils respectively. the number of turns per volts in the primary is equal to the number of turns per volts in the secondary.
Primary coil - 220 volt (PHILIPPINES Base)
Secondary coil - 12 volts
Number of turns (primary) = 220x10 = 2200 turns
Number of turns (secondary) = 12x10 = 120 turns
having computed for the number of turns in the primary and secondary coils. determine the sizes of wire for these coils in the next step . before computing for the guage or size of wire (AWG) must find out the current capacities of wires and their corresponding sizes. this data is provided in table 2 .
the power formula is used again in solving for the currents of wires in the primary and secondary. dividing the watts over voltage gives us the current of the wire:
note:
I = Current, W = Wattage, E = Voltage
I = w/e
I secondary = 9watts/12volts = .75 a
I primary = 9watts/220volts = .04a
after having solved for the currents of wires pick up the corresponding sizes of wires from table 2. choose the closest current listed in the table.
Size of wires (Primary) - #35
Size of wires (Secondary) - #23
in case of a multi-voltage secondary, the higher voltage should be taken for computation. if the transformer has multiple secondary coils, the wattage of each coil is computed and then summed up. in other words, the wattage of the primary is equal to the total wattage of all secondary coils.
if the secondary coil is only center-taped, half of the wattage and current is taken to compute for the wattage of that coil.
the primary is 220-0 volts, the secondary is 12-0-12 volts
