Grade 9 · From USB to Field System: ESP32 water quality

Battery safety and fuses

Follow the student handout to build, test and document this stage of the water-quality system.

Prepared lesson material. Start this task when your teacher introduces it; it is not currently assigned homework.

For this lesson

2 pages · Use the handout for the complete instructions, examples and response spaces.

Read the handout text online

For diagrams, visual examples and the full layout, open the handout above.

Lesson 3: Battery Safety, Switches, and Fuses

Protected power build and inspection record

Grade 9 MYP Design | From USB to Field System

Name: __________________

Class / team: __________________

Date: __________________

Today’s goals • Explain how a fuse protects wiring. • Build the positive and negative distribution paths. • Pass an unpowered inspection.

Non-negotiable rule The battery stays disconnected while wiring changes are made. Teacher approval is required before power is applied.

BATTERY_POS -> MAIN_SWITCH.INMAIN_SWITCH.OUT -> FUSE_3A.INFUSE_3A.OUT -> POSITIVE_DISTRIBUTIONBATTERY_NEG -> NEGATIVE_DISTRIBUTION

☐ Battery is disconnected.

☐ Positive and negative wires use clear color labels.

☐ Switch is in series with battery positive.

☐ Fuse is after the switch and before downstream distribution.

☐ Positive and negative are in separate WAGO/terminal blocks.

☐ No loose copper strands are visible.

☐ No conductor can touch the opposite polarity.

Check	Method	Result	Teacher initials
Polarity and labels	Visual
Fuse location	Netlist + visual
Switch operation	Continuity, unpowered
Positive-to-negative short	Continuity/resistance, unpowered
Wire retention	Gentle pull test

Why must the fuse be close to the positive source rather than near the final component?

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What can a fuse protect against, and what can it not protect against?

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A student says, “It is only 12V, so it cannot be dangerous.” Write a technically accurate response.

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