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Name___________________________
Time Block_________
CTC Truck and Diesel Watts Homework 15 points possible
Watts are the standard unit of measurement of electrical power. One watt is one
ampere of current flowing at one volt. Watts are typically rated as AMPS x VOLTS
or VOLT-AMP (V-A) (From TechEncyclopedia). Watts are used in many automotive
applications from light bulbs to stereo systems. Computer systems monitor the
amperage flow through different circuits to determine if systems are working
properly or not. Replacing a light bulb with one that has a different wattage can
cause the computer to indicate a failure in the lighting system. Installing a new
stereo system to a circuit that is not designed to handle additional amperage can
cause damage to the circuit.
If someone wanted to install this stereo system in a vehicle how would they know
how many amps the system will draw on a circuit it is hooked up to? Amplifiers are
rated in Watts. In this picture we have a 4 channel amp and a mono amp driving
all of the speakers. Since there are no speakers hooked up to the Receiver it will
only draw about 2 amps at the most. Let’s say that the 4 channel amp is rated for
225 watts per channel maximum output and the mono subwoofer amp is rated for
600 watts maximum. (Amp is short for Amplifier; don’t confuse the name Amp with
the electrical term Amps (short for Amperage) which is current flow).
First of all we need to know the total maximum watts which is all of the channels of
the 4 channel amp added up and then add to the maximum watts of the mono amp
= _______________ watts (2pts.)
Second we need to know our voltage with the engine running which is about 14
volts.
Now we take the total wattage and divide by the voltage to see how many amps of
current the stereo system amplifiers will draw at their maximum output
________________ (2pts.) and then remember to add the 2 amps for the Receiver for
our stereo system total maximum amperage draw ________________ (1pts.)
Let’s say its night time. The stereo is on near maximum, the fog lights are on (2 x
55 watt bulbs) the head lights are on (2 x 75 watt bulbs), the parking and tail light
bulbs (8 x 7 watt bulbs) and the heater blower motor is running (15 amps).
How many amps do the fog lights draw? _______________ (2pts.)
How many amps do the head lights draw? _______________ (2pts.)
What is the total amperage of all the lights? _______________ (2pts.)
What is the total amperage of the lighting system, blower motor and stereo system
combined? _______________ (2pts.)
If the Alternator maximum output is 120 amps (at 14 volts) what is the difference
between our charging system output and the total draw on the system?
_______________ (2pts.)
A big advantage of LED lights is that they draw very little current. If a vehicle has
a lot of lighting and uses LED lights it can significantly reduce the total draw on the
charging system.