If a marine radiotelephone receiver uses 75 watts of power and a transmitter uses 325 watts, how long can they both operate before discharging a 50 ampere-hour 12 volt battery?
• Power (watts) and how it relates to current (amps) and voltage (volts) • How to use battery capacity in ampere-hours (Ah) to find time • Adding transmitter and receiver loads together to get total power/current
• How can you convert the power used by the radio (in watts) and the battery voltage (in volts) into current draw (in amps)? • Once you know the total current draw, how do you use the 50 ampere-hour rating to find how many hours the battery can supply that current? • Are you remembering to combine BOTH the transmitter and receiver power when calculating total load on the battery?
• Use the relationship P = V × I to find current from power and voltage • Make sure you add the receiver and transmitter power before converting to current • When using ampere-hours, check that your final step is time = capacity (Ah) ÷ current (A) and then convert hours to minutes if needed
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