Current and amperage
Why can a tiny sensor use milliamps while a starter motor can pull 200–400+ amps from the same 12 V battery?
What this lesson covers
CORE TEACHING Current; load demand; resistance; power relationship at a practical level; mA vs A; in-series measurement; clamp measurement; excessive current. Add V=IR and P=VI using actual vehicle examples; explain series current vs parallel branch current; current division; why lower resistance generally allows more current at the same system voltage. PRACTICAL DEMONSTRATIONS AND TESTS Measure current of bulb/small motor; starter current with clamp; compare healthy vs stalled/high-current motor if available. Use two bulbs in parallel and compare total current with one bulb; calculate one simple starter/blower example without turning the lesson into classroom maths. ADVANCED / SCAN TOOL LAYER Use current waveform concept: motors, injectors and fuel pumps can reveal mechanical/electrical condition from current patterns. KEY DIAGNOSTIC QUESTIONS How much current should this load need? Is current too high, too low, or zero? What would each tell me? MUST-COVER CHECKPOINTS Start with the complaint; draw the circuit; identify expected inputs/outputs; perform physical tests; interpret evidence; prove the failed section; retest after repair.
What you will be able to do
Why can a tiny sensor use milliamps while a starter motor can pull 200–400+ amps from the same 12 V battery?
Where it sits in the programme
- Builds on
- Lesson 5: Multimeter use without blowing it up
- Feeds into
- Lesson 7: Complete starter motor diagnosis