phsautomotivesalsphsautomotivesals basic electricity circuits ohms law and formulas

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Basic Electricity

Circuits

Ohms Law and formulas

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(I or A) Current ‑ Flow of electrons through a conductor as a result of pressure applied ‑I‑ Intensity -A- Amperage

(E or V) Voltage ‑ Force or electrical pressure that moves electrons ‑E‑ Electromotive force -V- Voltage

(R) Resistance ‑ Opposition to current flow or electrical restriction

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Series Circuit ‑ Single path same current flows through each

component

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Series Circuit Laws

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E = volts Most auto techs use the letter V

The sum of the individual voltage drops in a series circuit equals the

applied voltage.

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Two Definitions you will need to know when dealing with voltage.Open Circuit Voltage or OCVVoltage when no load is applied to the car. Applied Voltage Voltage when a load is applied to the car. (Headlights are on)

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I = current or amps Most auto techs use the letter A

In a series circuit, the current flowing in the circuit is the same

at any point.Terms to know

Note It = current Total

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R = resistance Individual resistance in a series circuit add up to the total circuit resistance.

Rt = R1 + R2+ R3

Terms to know

Rt = Resistance Total

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Parallel Circuit ‑ More then one path, voltage is the same at each

branch of the circuit.

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Parallel Circuit Laws

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E = volts In a parallel circuit, the voltage is the same across

each branch.

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I = current or amps The total current in a parallel circuit is

equal to the sum of the individual branch currents.

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R = resistance The total resistance in a parallel circuit is

always less than the smallest resistive branch

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Series parallel, combination of

both circuits

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It takes one volt to push one amp though one ohm of resistance

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Ohm’s Law

to find E = I x R

I = E ÷ R

R = E ÷ I

E

I x R

Amperes = I - Intensity

Volts = E - Electromotive force

Ohms = R - Resistance

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Ohm’s Law For Auto techs’

to find V = A x R

A = V ÷ R

R = V ÷ A

V

A x R

Amperes = A - Amperage

Volts = V - Voltage

Ohms = R - Resistance

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Series CircuitResistance TotalRt = R1 + R2+ R3

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R1 = 1002R2 = 99R3 = 984Rt = 2085

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Series Circuit Current Total

Et It= Rt

It = Amps Total

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R1= 2 ΩR2= 2 ΩR3= 2 ΩRt= 6 Ω

V or E = 12

Et 12 2 It= Rt 6

R1 = 2 Ω

R2 = 2 Ω

R3 = 2 Ω

Series Circuit Current TotalExample

12V

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Series Circuit Voltage drop across each resistor

E= It X R1

E= It X R2

E= It X R3

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R1= 2 ΩR2= 2 ΩR3= 2 ΩRt= 6 Ω

R1 = 2 Ω

R2 = 2 Ω

R3 = 2 Ω

Series Circuit Current TotalExample Finding Volts

It X R1 = E2 X 2 = 4It X R2 = E 2 X 2 = 4It X R3 = E2 X 2 = 44+4+4= 12 Volts

It = 2

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R1= 2 ΩR2= 4 ΩR3= 6 ΩRt= 12 Ω

R1 = 2 Ω

R2 = 4 Ω

R3 = 6 Ω

Series Circuit Current TotalExample 2

It X R1 = E1 X 2 = 2It X R2 = E 1 X 4 = 4It X R3 = E 1 X 6 = 62+4+6 = 12 Volts

It = 1

12V

Et 12 1 It= Rt 12

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To find Voltage drop across each resistor you first must find It . Take Voltage (12) and divide by Rt Which is 10 the answer is 1.2 = It

Then take It X R1 = Voltage drop of R1

1.2 X 2 = 2.4

It X R2 = Voltage drop of R2

1.2 X 4 = 4.8

It X R3 = Voltage drop of R3

1.2 X 4 = 4.8 2.4 + 4.8 + 4.8 = 12

R1 = 2 Ω

R2 = 4 Ω

R3 = 4 Ω

12V

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• If there are only 2 resistor’s and they are the same size just take voltage divide by 2 and you have voltage drop V ÷ 2

• Any number of Resistor’s all the same size. V ÷ # of Resistor’s = Voltage Drop

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R1 x R2

Rt = ----------- R1 + R2

Parallel circuitResistance Total

if only 2 Resistors

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R1 x R2

Rt = ----------- R1 + R2

R2 = 4 Ω

R1 = 2 Ω

2 X 4 = 8Rt 1.33 = -------------- 2 + 4 = 6

Note Rt is less the Smallest resistor

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if 3 or more Resistors

1 _ 1 1 1 1 R1+ R2+ R3+ R4

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Rt if 3 or more Resistors 1 _ 1 1 1 R1+ R2+ R3

R1 = 2 Ω

R2 = 4 Ω

R3 = 6 Ω

1 _ 1 1 1 2 + 4 + 6

1 .5 + .25 + .167

1_ .917

Rt = 1.09 Ω

==

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if Resistors are all the same value

Value of one Resistance Rt= ------------------------------ Number of Resistances

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Parallel circuitCurrent flow

Et It= Rt

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Parallel circuitCurrent flow

Et It= Rt

12V 6A = 2 Ω

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Parallel circuitCurrent flowof a branch

I branch a = E R1

I branch b = E R2

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The Power Triangle or Joules Law

• For calculating using

• Power (W) Current (A) and voltage (V)

• Used in the same way as the Ohms Law triangle we can use the same method to see the relationship between power (W), current (A) and Voltage (V).

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The Power Triangle• Power = Current x Voltage

• P = A x V

• Current = Power over Voltage

• A = P ÷ V

• Voltage = Power over Current

• V = P ÷ AP

A x V

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The Power Triangle

• P = Watts

• Horsepower (hp) Some electrical devices such as electric motors have a power (W) rating in horsepower to which a conversion of 1hp=746W would be required for calculations.

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The history of the terminology • Each of the units of measurement are named after famous experimenters in

electricity and energy

• Voltage, Volts (V) named after the Italian Alessandro Volta known especially for the development of the first electric cell or modern translation "the battery" in 1800.

• Amps (A) named after the Frenchman Andre M.Ampere one of the main discoverers of electromagnetism.

• Ohms (Ω) named after the German Georg Simon Ohm a physicist who began his research with the recently invented electrochemical cell (invented by the Italian Alessandro Volta). Using equipment of his own creation, Ohm determined that there is a direct proportionality between the potential difference (Voltage) applied across a conductor and the resultant electric current now known as Ohms Law.

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The history of the terminology • Each of the units of measurement are named after famous experimenters in

electricity and energy

• Watts (W) named after the Scotish inventer and mechanical engineer James Watts who's name was adopted as a measurement by the second congress of the British association for the advancement of science in 1889.

• Joule (J) named after the English physicist James Prescott Joule in recognition of his work on heat and it's relationship to mechanical work or energy.

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The end

Thanks to the toolboxshop.com for the info on power

http://www.thetoolboxshop.com/guides-3-w.asp

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