1

Applying Math to Wire Sound

Using formulas and conversions to wire up sound

2

Problem We have a classic Camaro and we will be

installing a 1200 watt amp and a head unit that is rated at 100 watts.

What size alternator will be needed to ensure proper operation of the charging system?

How much circuit protection will be needed to ensure proper operation?

3

Seen this in math? Convert 4500cc to in3. 1 in3 = 16.387cc

16 = 5y, Solve for y.

333

608.274387.16

4500387.161

14500 inin

ccincc

2.3516

y

4

Math Terms Ohms Law: E = I x R E = Voltage I = Amps R = Ohms

Watts Law: W = E x I W = Watts E = Volts I = Amps

5

Horse Power 1 Hp = 746 Watts One Hp can raise

550 lbs 1 foot in one second

6

Applying Ohms law & Watts law

Ohm’s Law : E = I x R• 1998 Ford F-150 needs 180 starting amps to crank

the engine. What is the resistance if the voltage is 12V?• 12 = 180 x R

ohmsR 07.018012

7

Applying Ohms law & Watts law Watts Law: W = E x I If a 500 watt speaker

need 10 amps to operate, what is the voltage requirement?• 500 = E x 10

E

E

5010500

8

Applying Unit Conversions A10,000 watt lighting

system is being installed on and off road Chevy Silverado. How much horsepower is being used to power these lights if the available voltage is 12 volts?• 1 horsepower = 746

watts

hphpwattshpwatts 4.13

74610000

7461

110000

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Let’s look at the original problem again! We have a classic Camaro and will be

installing a 1200 watt amp and a head unit that is rated at 100 watts.

What size alternator will be needed to ensure proper operation of the charging system?

How much circuit protection will be needed to ensure proper operation?

10

Calculations Given values

• 12 volt system• 80 amp alternator• We will be adding

1300 watts in sound

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Using Watts law to find the total amperage needed for the sound system Recall, Watt’s Law:

W=E x I Watts = Voltage X

Amperage Total wattage added =

1300 Voltage = 12 1300 Watts Divide by

12 Volts = 108 Amps The system will require

108 amps working at max output

33.108121300

I

12

Calculating Total System Amperage We need to find the reserve amperage of

our camaro. We know the alternator is rated at 80

amps and by researching our stock vehicle option package our peak draw is 60 amps so our reserve would be 20 amps.

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Putting it All Together System voltage = 12 volts Total Amp draw of our stock car = 60 amps Our reserve = 20 Amps Our new system will require 108 amps max

for a total of 1300 Watts By adding 108 amps to our car the total peak

demand would be 168 amps. Add in our reserve and our Camaro will need

a 188 amp Alternator to operate under peak load.

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What will this cost us in performance? 1300 watts divided by 746 = 1.74

horsepower

hphpwattshpwatts 74.1

7461300

7461

11300

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Try This Problem…. A vehicle with a 12 volt

system and a 100 amp alternator has the following circuits: 30 amp a/c heater

30 amp power window/seat 15 amp exterior lighting 10 amp radio 7.5 amp interior lighting

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Name: ___________________

1) Find the total resistance of the entire electrical system based on the car’s system described above.

2) Find the unused amperage if all of the above circuits are active.

3) If a 1000 watt amplifier is added to the audio system, how much unused amperage (negative or positive) will be left?

4) Will a larger amp alternator be required to operate the circuits? If yes, calculate the minimum amperage needed?

5) If a larger alternator is needed and given alternators come in 100 amp intervals, what size alternator do you need to fulfill the requirements of the charging system?

6) You have successfully installed your amplifier. Should you be concerned about a reduction in horsepower? To answer this question calculate the following:

– Based on the original alternator size, how much horsepower is being used by the alternator?

7) By adding the new alternator, how much horsepower will the engine lose if the total engine horsepower equals 385 hp?

17

Now it is your turn…..

Think of a problem similar to the car stereo problems we have solved today or even one you have experienced yourself.

Write it up and make your recommendations for how to solve the problem, be sure to show your work as we have in this lesson.