The electrical units for power, current, voltage and resistance are interlinked, so that when one alters it changes the values of all the other variables in the circuit. Watts, the units of power, are linked to milliamperes, often shortened to milliamps or ma, because Ohm's Law states that Watts / Volts = Amps. You can calculate the current flowing through the component if the wattage and voltage are known.
- Skill level:
- Moderately Easy
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Things you need
Establish the wattage to convert to milliamps, and the voltage applied to the circuit. For example, a circuit consisting of a 24-watt bulb powered by a 12-volt battery has a wattage of 24 and a voltage value of 12.
Divide the watts by the voltage to calculate the current. In the example from Step 1, 24 watts / 12 volts resolves to a current of 2 Amps.
Multiply the current value in Amps by 1,000 to convert it to milliamps. A milliamp is 1/1,000 of an Amp. In the previous example, a 24-watt load, with a 12-volt power supply, uses a current of 2,000 ma.
Tips and warnings
- The relationship between watts, volts, amps and ohms is expressed by Ohm's Law, Voltage = Current x Resistance. Electricians rearrange the law to solve equations involving power, current, voltage or resistance.
- Always use the correct arrangement of the Ohm's Law formula when converting between electrical units.
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