1. Electrical Basics
Power & Ohm’s Law

2. Group 1 Work together to understand the information in your section.
You will have 10 minutes to review the material and present it to the class.

3. Current
With some applied force, electrons will move from a negatively charged atom to a positively charged atom. This flow of electrons between atoms is called current.
Current is represented by the symbol I

4. Voltage
When there is a lack of electrons at one end of a conductor and an abundance at the other end, current will flow through the conductor. This difference in “pressure” is referred to as voltage.
This “pressure” is sometimes referred to as “electromotive force” or EMF.
Voltage is represented by the symbol E

5. Resistance
Resistance is the opposition to the flow of electrons (aka “current”).
Every material offers some resistance.
Conductors offer very low resistance.
Insulators offer high resistance.
Resistance is represented by the Symbol R
Resistance is measured in Ohms Ω

6. Measuring Current
Current is measured by literally counting the number of electrons that pass a given point.
Current will be the same at any point of a wire.
The basic unit for counting electrons is the "coulomb“.
(French physicist Charles Augustin de Coulomb in 1780’s)

7. Measuring Current (cont)
1 coulomb = 6.24 x 1018 electrons = 6,240,000,000,000,000,000
= more than 6 billion billion electrons!
If 1 coulomb of electrons go by each second, then we say that the current is 1 "ampere" or 1 amp
(Named after André-Marie Ampère, 1826)

8. Measuring Voltage Voltage is measured in volts.
A voltage of 1 volt means that 1 "Joule" of energy is being delivered for each coulomb of charge that flows through the circuit.
A “Joule” is the basic unit of energy in the metric system - its about the amount of energy it takes to lift two pounds a height of 9 inches.
(Named after James Prescott Joule)

9. Measuring Resistance Resistance is measured in ohms.
Symbolized with the letter “R” or with the
symbol “Ω”
(Named after the German physicist Georg Ohm, 1827)

10. Key Terms Conductor Allows the Flow of Electrons Insulator-
Stops/ Minimizes the Flow of Electrons
Resistor
Resists the Flow of Electrons
Semi-Conductor
Acts as both a Conductor / Insulator
Diode
Stops the flow of Electrons in one direction
Capacitor
Stores excess voltage
Shunt
Redirects the Flow of Electrons when triggered

11. Key Conversions Standard Test Conditions (STC)
A set of reference measurement conditions.
(25° C, or 77° F, 1000 W/m2, AM1.5 (air mass) )
1 Meter = 3.28 Feet
1 cm = Inches
1 Amp x 1 Volt = 1 Watt (Power)
1 HP = 746 Watts
Standard Operating Conditions (NOC)
A more realistic set of reference conditions.
(25° C or 77° F, 800 W/m2, 1 m/s wind speed)

12. Key Conversions Degrees Fahrenheit = (1.8 x C°) + 32
Degrees Celsius = (F° – 32) x 0.555
1 Langley = W/m2
(Unit of energy distribution over an area. This unit is used to measure solar irradiation or “insolation”.
1 kWh/m2 = 3.6 MJ/m2

13. Group 2 Work together to understand the information in your section.
You will have 10 minutes to review the material and present it to the class.

14. OHM’S LAW
A battery is a collection of cells that are contained in the same case and connected together electrically to produce a desired voltage. A battery cell is the basic unit in a battery that stores electrical energy in chemical bonds and delivers this energy through chemical reactions. Battery designs can vary by type and manufacturer, but many share the same basic components and store electricity using similar electrochemical reactions. See Figure 6-1.
Chapter 6-14

15. Ohm’s Law How is resistance, voltage, & current related? E = I R Or…
E = I x R
where: E = voltage in volts
I = current in amps
R = resistance in ohms

16. Ohm’s Law Using E = I R E = .003 (I) x 3,000 (R) E = 9 volts (or 9 v)
By the way...
“milli” = 1/1000
So a milli-Amp
Is 1/1000 of an amp
1mA = 1/1000A
or .001A
Using E = I R
E = .003 (I) x 3,000 (R)
E = 9 volts (or 9 v)

17. Ohm’s Law
What if you know the voltage & resistance but not the current?
What if you know the voltage & current but not the resistance?

18. Ohm’s Law
Knowing any 2 values, E, I, or R one can find the 3rd one by simple algebraic manipulation of the formula E= I x R
DEFINITIONS:
>An arithmetic operation is +, -, x, or ÷
>The opposite operation of:
+ is –
x is ÷
- is +
÷ is x

19. Ohm’s Law To manipulate the formula E = I / R…
RULE: Whatever arithmetic operation is done to one side of the equation must be done to the other side.
So…
E = I x R
Becomes…
I = E / R or R = E / I

20. Ohm’s Law R = E / I R = 9 (E) / .003 (I)
By the way...
“k” = 1000
So…
3k = 3,000
3kA = 3,000 amps
3kV = 3,000 volts
3 kΩ = 3,000 ohms
R = E / I
R = 9 (E) / .003 (I)
R = 3,000 ohms (or 3k ohms or 3k Ω)

21. Ohm’s Law I = E / R I = 9 (E) / 3,000 (R)
I = .003 amps (or .003A or 3 milliamps or 3 mA)

22. Ohm’s Law (cont)
For those who are not comfortable with algebra, there's a trick to remembering how to solve for any one quantity, given the other two...

23. Ohm’s Law (cont)

24. Group 3 Work together to understand the information in your section.
You will have 10 minutes to review the material and present it to the class.

25. Power
Sometimes we want to know the rate at which energy is delivered, not how much energy is delivered per coulomb of charge.
The rate at which energy is delivered is called power.
Power is defined as: Power = Energy / Time.

26. Power
The unit of power corresponding to 1 joule per second is called a “watt”.
1 watt = 1 joule per second.

27. Power Remember… Voltage “V” tells us the number of joules per coulomb
Current tells us the number of coulombs per second
So…
Power = number of watts = number of joules/second 
= joules/coulomb x coulombs/second = V x I

28. Power I = current in amps (A) V = voltage in volts (V)
Or the power formula…
P = I x V Or
P = IV
Where P = power in watts (W)
I = current in amps (A)
V = voltage in volts (V)

29. Power What if you know the power & voltage but not the current?
What if you know the power & current but not the voltage?

30. Power
Knowing any 2 values, P, I, or E, one can find the 3rd one by simple algebraic manipulation of the formula P=I E
DEFINITIONS:
>An arithmetic operation is +, -, x, or ÷
>The opposite operation of:
+ is –
x is ÷
- is +
÷ is x

31. Power To manipulate the formula P = I x E…
RULE: whatever arithmetic operation is done to one side of the equation must be done to the other side.
So…
P = I x E
Becomes…
I = P / E or E = P / I

32. Power
Additional Power Formulas

33. Group 4 Work together to understand the information in your section.
You will have 10 minutes to review the material and present it to the class.

34. SERIES DC CIRCUITS
&
PARALLEL DC CIRCUITS

35. What are “series” & “parallel” circuits?
Two basic ways to connect more than two circuit components: series & parallel.
These components can be electronic components such as resistors & capacitors or they can be power sources such as batteries, solar cells, or solar modules.
Self-discharge is the gradual reduction in the state of charge of a battery while at steady-state condition. Self-discharge is also referred to as standby or shelf loss. Self-discharge is a result of internal electrochemical mechanisms and losses. The rate of self-discharge differs among battery types and increases with battery age. Self-discharge rates are typically specified in percentage of rated capacity per month. Higher temperatures result in higher self-discharge rates, particularly for lead-antimony designs. See Figure 6-8.

36. SERIES CIRCUITS
The defining characteristic of a series power circuit is that there is only one path for electrons to flow.
The power sources are connected end-to-end in a line to form a single path for electrons to flow…
Temperature and discharge rate affect capacity. Warmer batteries are capable of storing more charge than colder batteries. See Figure 6-3. However, high temperatures decrease the useful life of a battery. Manufacturers generally rate battery performance and cycle life at 25°C (77°F). For the best trade-off between capacity and lifetime, the system should be designed for the recommended discharge rate and the battery should be located where the average temperature will be close to the manufacturer’s recommendation. Any differences from the rated conditions affect the actual capacity of the battery.

37. Series Rule #1
The total output current (measured in amps) is equal to the individual power source.
By the way...
“milli” = 1/1000
So a milli-amp (mA)
Is 1/1000 of an amp
Temperature and discharge rate affect capacity. Warmer batteries are capable of storing more charge than colder batteries. See Figure 6-3. However, high temperatures decrease the useful life of a battery. Manufacturers generally rate battery performance and cycle life at 25°C (77°F). For the best trade-off between capacity and lifetime, the system should be designed for the recommended discharge rate and the battery should be located where the average temperature will be close to the manufacturer’s recommendation. Any differences from the rated conditions affect the actual capacity of the battery.
150 mA
150 mA
150 mA
150 mA
Chapter 6-37

38. Series Rule #2 The total output voltage
(measured in volts) is equal to the sum of the individual power sources.
150 mA
150 mA
150 mA
150 mA

39. Series Power Sources
150 mA
Each cell?

40. Each solar panel = 4 VDC @ 100mA
Series Power Sources
Total?
Each solar panel = 4 100mA

41. Parallel Circuits
The defining characteristic of a parallel power circuit is that all the positive terminals are connected together and all the negative terminals are connected together…
Temperature and discharge rate affect capacity. Warmer batteries are capable of storing more charge than colder batteries. See Figure 6-3. However, high temperatures decrease the useful life of a battery. Manufacturers generally rate battery performance and cycle life at 25°C (77°F). For the best trade-off between capacity and lifetime, the system should be designed for the recommended discharge rate and the battery should be located where the average temperature will be close to the manufacturer’s recommendation. Any differences from the rated conditions affect the actual capacity of the battery.
Chapter 6-41

42. Parallel Circuits Parallel Rule #1
The total output current (measured in amps) is equal to the sum of the currents of the individual power sources.
1.5 VDC
1.5 VDC
1.5 VDC
150 mA
150 mA
150 mA

43. Parallel Circuits Parallel Rule #2
The total output voltage (measured in volts) is equal to the voltage of the individual power sources.
1.5 VDC
1.5 VDC
1.5 VDC
150 mA
150 mA
150 mA

44. Parallel Circuits
600 mA
Each cell?

45. Each solar panel = 4 VDC @ 100mA
Parallel Circuits
Total?
Each solar panel = 4 100mA

46. Series or Parallel?

47. SERIES / PARALLEL CIRCUITS
We can have circuits that are a combination of series and parallel to increase both amperage (current) and voltage…
Temperature and discharge rate affect capacity. Warmer batteries are capable of storing more charge than colder batteries. See Figure 6-3. However, high temperatures decrease the useful life of a battery. Manufacturers generally rate battery performance and cycle life at 25°C (77°F). For the best trade-off between capacity and lifetime, the system should be designed for the recommended discharge rate and the battery should be located where the average temperature will be close to the manufacturer’s recommendation. Any differences from the rated conditions affect the actual capacity of the battery.
Chapter 6-47

48. Each solar panel = 4 VDC @ 100mA
SERIES / PARALLEL CIRCUITS
Temperature and discharge rate affect capacity. Warmer batteries are capable of storing more charge than colder batteries. See Figure 6-3. However, high temperatures decrease the useful life of a battery. Manufacturers generally rate battery performance and cycle life at 25°C (77°F). For the best trade-off between capacity and lifetime, the system should be designed for the recommended discharge rate and the battery should be located where the average temperature will be close to the manufacturer’s recommendation. Any differences from the rated conditions affect the actual capacity of the battery.
Each solar panel = 4 100mA
Chapter 6-48

49. RULE SUMMARY: Series Circuits
The total output current (measured in amps) is equal to the individual power source.
The total output voltage (measured in volts) is equal to the sum of the individual power sources.

50. RULE SUMMARY: Parallel Circuits
The total output current (measured in amps) is equal to the sum of the currents of the individual power sources.
The total output voltage (measured in volts) is equal to the voltage of the individual power sources.

51. Group 5 Work together to understand the information in your section.
You will have 10 minutes to review the material and present it to the class.

52. FORMULA SUMMARY
Ohm’s Law:
E = I * R
I = E / R
R = E / I

53. FORMULA SUMMARY Power: I = P / E P = E2 / R E = P / I
P = I x E P = I2 x R
I = P / E P = E2 / R
E = P / I

54. FORMULA SUMMARY
Resistance in a Series Circuit:

55. FORMULA SUMMARY
Resistance in a Parallel Circuit: