In agricultural circuits the voltage is determined by the source of the electrical energy. Standard domestic service is 120 or 240 V. Agricultural equipment may have electrical systems that operate on 6, 12, 24, or 48 V.
Amperage is determined by measuring the circuit with an ammeter or by calculations using Ohm's law, E = I x R. In Ohms law "E" stands for electrical motive force, in volts, "I" is intensity, in amperage or amps, and "R" is resistance, measured in Ohms. When the resistance is known, the amperage can be determined by rearranging Ohm's law. The total amperage of a circuit can be calculated by dividing the source voltage by the total resistance of the circuit. Rearranging Ohm's law for amperage:
Problem: Determine the total amperage for the series circuit illustrated in Figure 26.5. Use 120 V for the source.
Solution: Using Ohm's Law:
I (amp) = —--- =-=-= 12.371- ■ ■ or 12 amp v R (Ohms) 2.5 Q + 3.2 Q + 4.0 Q 9.7 Q v
A circuit with 9.7 Q of resistance and a source voltage of 120 V will have a current flow of 12 amps.
The same procedure is used to determine the amperage of a parallel circuit. The source voltage is divided by the total resistance in the circuit.
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