10 bite-sized lessons
Select a lesson. Mark it complete when you can explain the key idea in your own words.
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4-pin & 5-pin automotive relay
Operate a ground-switched relay. A protected, constant 12 V feed powers terminal 30 and one side of the coil (86). The control switch grounds terminal 85. When energized, terminal 30 connects to 87; on the 5-pin changeover relay, 30 disconnects from normally closed 87a.
*Voltage measured from terminal 87 to chassis ground, with the lamp/load attached. Illustrative ideal 12 V source; high-resistance fault modeled as a series 2 Ω contact.
Keyed voltage to chassis ground (simplified circuit).
Solenoid actuation & flyback
A solenoid uses current through a coil to generate a magnetic field and move a plunger. This simplified teaching model shows trends rather than predicting the exact force or travel of a specific automotive solenoid.
With a suitable diode across a DC coil, current recirculates and decays, limiting switch voltage. The plunger may release more slowly.
What changes with PWM?
Pulse-width modulation switches the supply on and off. Duty cycle changes average electrical input and can change holding force or position, depending on driver circuitry, mechanical load, inductance and frequency. It does not make the instantaneous ON current equal to duty cycle × V/R.
For the simple idealized model shown here: ON current = V/R; average input power ≈ duty × V²/R. Real inductive current and heating depend on waveform and driver design.
Follow the evidence
For each case, interpret the observations and pick the next justified diagnosis or test. Each case can be completed once for progress; revisit it as often as you want.
What does the evidence support?
Prove you can explain it
Answer all 10 questions. Score at least 8/10 to earn the in-browser mini-course badge. The knowledge check assesses concepts, not hands-on technician certification.
Course completion
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