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Basic DC Electricity

Wednesday September 13th 2023

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Welcome

Please share the following in the chat:�

your name and preferred pronouns
school and school location
grade level and subject you teach
which emoji represents your feelings about teaching electricity?

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Land Acknowledgement

We are currently on unceded Lisjan Territory of Huchuin that is now known as Oakland, Berkeley, Alameda, Piedmont, Emeryville and Albany, California. The Confederated Villages of Lisjan are one of many Ohlone nations.

Whose land are you on? Visit native-land.ca or google Native Land Digital.

Visit https://sogoreate-landtrust.org/

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Learning Objective and Agenda

CCC 3 �Scale, proportion and quantity

SEP 5 �Using mathematics and computational thinking

Teachers will be able to describe and explain the relationships between voltage, current and power by using mathematics and computational reasoning so that they can track how power is transferred between components in a stand alone solar system

5E lesson plan

DCI PS3 Energy

Agenda

Engage - Fatal Electricity
Explore - Voltage, current and power
Explain - Series and Parallel Wiring
Elaborate - Charging using a DC outlet
Evaluate - Quiz!

Norms

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Need help accessing �our curriculum? �Please stay on at the end!

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Fatal Electricity

Which of the following statements do you �think is most correct?

For a person to be injured or killed by an electric current there needs to be both a high voltage and a high current
It doesn’t matter whether the current or voltage is high; it’s the product of these two values - a high transfer of power will injure or kill you
A very small current can kill you if it is pushed through your body with a high enough voltage
A large current will kill you even if the voltage is low�

ENGAGE

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Fatal Electricity

Which of the following statements do you think is most correct?

For a person to be injured or killed by an electric current there needs to be both a high voltage and a high current
It doesn’t matter whether the current or voltage is high; it’s the product of these two values - a high transfer of power will injure or kill you
A very small current can kill you if it is pushed through your body with a high enough voltage
A large current will kill you even if the voltage is low�

Source: OSHA Basic Electricity Safety

“In industry, 30 volts is generally considered to be a conservative threshold value for dangerous voltage. The cautious person should regard any voltage above 30 volts as threatening, not relying on normal body resistance for protection against shock.” Source

ENGAGE

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Calculating Voltage, Current and Power

EXPLORE

Voltage (V)	Current (A)	Power (W)
12 V	0.5 A
	2 A	6 W
12 V		12 W
12 V		60 W
	1.2 A	6 W

Complete on Jamboard

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Calculating Voltage, Current and Power

EXPLORE

Voltage (V)	Current (A)	Power (W)
12 V	0.5 A	6 W
3 V	2 A	6 W
12 V	1 A	12 W
12 V	5 A	60 W
5 V	1.2 A	6 W

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VOLTAGE and CURRENT Water Analogy

High Voltage

Low Voltage

High Current

Low Current

EXPLORE

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VOLTAGE and CURRENT Fulcrum Analogy

EXPLORE

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SERIES and PARALLEL WIRING

EXPLAIN

What does this analogy tell us about how voltage and current are combined in series wiring and in parallel wiring?

How is power generation affected by different wiring methods?

Which is the safe way to wire solar panels?

Solar panels in series

Solar panels in parallel

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SERIES and PARALLEL WIRING

EXPLAIN

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Charging using a DC outlet

ELABORATE

All DC USB outlets are 5V

Battery in the Solar Suitcase is 12V

If you have a 0.5A current running from the charge controller to the load then what current is being transferred from the USB charger to a phone which is plugged in to charge?

What value remains constant through this transfer of energy?�

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Charging using a DC outlet

12V x 0.5A = 6W

5V x 1.2A = 6W

Cell phone battery is about 4 Amp hours, how long will an empty battery take to fully charge if it is receiving a current of 1.2 A?

ELABORATE

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Quiz time!

EVALUATE

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Additional Reference Slides Below

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DIRECT CURRENT VS ALTERNATING CURRENT

Credit: https://evenmix.com/ac-vs-dc-current/

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VOLTAGE�measured in Volts (V)

CURRENT�measured in Amps (A)

image: www.circuitbread.com

Two analogies: Water/Pressure and Gravity/Force

The first term to review is voltage which is the force or electrical pressure behind the electrons. In order for electricity to move from a source to an appliance, it needs to have electrical pressure. Voltage is also described as Potential Difference, in DC electricity, the difference measured in voltage between two sides of a circuit, the positive and the negative. You can demonstrate this as height. If you lift a ball above the ground you are increasing the difference between the ball and the ground, so that when you drop the ball, it will hit with more force. If you lift the ball up 2 feet, you can call this 2 volts, and if you lift it up to 6 feet, it will be 6 volts, and thus have 3 times the difference and 3 times greater potential, and hit the ground with 3 times more force. So potential difference is related to force.

Electrical concepts are difficult to visualize, so often water analogies are used as a way to visualize what is happening in an electrical circuit. In these analogies, the water molecules represent the electrons and the water pipe represents the electrical wires.

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Which waterfall represents the higher voltage? Why?

VOLTAGE Water Analogy

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Which river represents the higher current? Why?

Can you make any comparisons of the “voltage”of these rivers?

CURRENT �Water Analogy

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POWER�measured in Watts (W)

These images show the same waterfall in different seasons.

Using the terms you have just learned, describe the similarities and differences.

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POWER�measured in Watts (W)

Power = Voltage x Current

Watts = Volts x Amps

(W) = (V) x (A)

High voltage

High current

High power

High voltage

Lower current

Lower power

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POWER�measured in Watts (W)

Power = Voltage x Current

Watts = Volts x Amps

(W) = (V) x (A)

Example: If you are drawing a 5A current from a 12V battery, what power are you producing?

Power = 12V x 5A� = 60W

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DEMONSTRATION OF POWER

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DEMONSTRATION OF POWER

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ENERGY

Watts x hours = Watt-hours (Wh)

Typical light bulb = 50 W

50 watts x 5 hours = 250 watt-hours

ELECTRICITY BASICS FOR SOLAR | 26

WSS LED = 5W

5 watts x 5 hours = 25 watt-hours

Watt-hours(Wh)

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DC Electricity resource page

Value Measured in Symbol

Voltage Volts (V) V

Current Amps (A) I

Power Watts (W) P

Energy Watt-hours (Wh) E

Equations

Power = Current x Voltage

Watts = Volts x Amps W = V x A

Energy = Power x Time

Watt-hours = Watts x hours Wh = Watts x hours