Batteries, Machines and Electricity Systems
Follow Energy Through an Electrical System
Trace sources, converters, controllers and loads without confusing energy roles.
You must choose between real alternatives covered by “Follow Energy Through an Electrical System” for a defined machine, circuit or installation.
Use an energy-path block diagram to diagnose an electrical system, distinguish component roles, and select measurements that test one boundary at a time without confusing isolation, command and power faults.
- Select or check first
- Trace function before naming a failed component. Define the expected input and output of each stage. Find the first boundary where valid input exists but the expected output does not. Then test the enabling conditions and load before condemning that stage.
- Controlling assumption
- Circuit state, waveform, source impedance, ratings, temperature and protection topology match the equipment being analysed.
- Top risk
- The map is not permission for live probing. Before opening equipment, identify all electrical, mechanical, thermal and stored-energy hazards.
- Proof
- Check the exact manufacturer data, units and limits, then verify the result by calculation, measurement or a controlled acceptance test.
Start with the basics Optional foundation before “Follow Energy Through an Electrical System”
Electrical-engineering basics
Electrical behaviour becomes easier to reason about when every voltage has a reference and every current has a complete return path.
- Voltage
- Voltage is potential difference between two points. A voltage statement is incomplete unless both points or its reference are known.
- Current
- Current is charge flow through a path. It does not disappear after a component; in a complete circuit it returns to the source.
- Resistance and impedance
- Resistance opposes steady current. Impedance extends that idea to changing signals and can depend on frequency through capacitance and inductance.
- Power and heat
- Electrical power is the rate of energy transfer. Some becomes useful output and some becomes heat that must stay within component and enclosure limits.
- Rating versus operating point
- A rating is a limit or qualified condition, not a target. The operating point must remain inside all relevant voltage, current, power, temperature and timing limits.
How to use this article: Draw the source, load, reference and return path before calculating. Treat exposed or stored electrical energy as hazardous until isolation is proved.
On this page
A symptom appears at the end of a chain, but its cause can be anywhere upstream. “The motor does not turn” might mean no stored energy, an open protection device, missing converted voltage, an absent command, a switch that cannot deliver current, a mechanical overload or a failed motor. A block diagram prevents random replacement by asking what energy and information should cross each boundary.
Build a six-stage diagnostic map
Diagram description
Blocks are labelled Supply, Conversion, Control, Switching, Load and Evidence, with isolation and stored-energy safety placed before measurement.
| Stage | Input question | Output evidence |
|---|---|---|
| Supply | Is the source present, connected and within its operating range? | Voltage under the relevant load; protection and return path intact |
| Conversion | Does the converter receive valid input and enable? | Correct rail, polarity, waveform and current capability |
| Control | Are sensors, references, interlocks and commands plausible? | A defined enable, duty, state or setpoint |
| Switching | Does the power device receive the command and have a complete power path? | Controlled voltage/current reaches the load |
| Load | Is it electrically and mechanically able to accept energy? | Current, torque, light, heat, motion or another intended conversion |
| Evidence | Is the observer trustworthy? | Independent measurement agrees with an indicator or reported state |
Component symbols make more sense when tied to energy roles
Diagram description
Five devices are paired with their dominant teaching role and a concise limitation, including the transformer requirement for changing flux and real losses in every device.
| Part | Useful role | Question that prevents a common mistake |
|---|---|---|
| Battery | Stores chemical energy and establishes a source voltage | Can it hold terminal voltage at the demanded current? |
| Inductor | Stores magnetic-field energy while current changes | Where can its current flow when a switch opens? |
| Transformer | Transfers AC or switched energy through changing magnetic flux | Is there changing flux, correct turns ratio and an allowed load? |
| MOSFET | Controls a power path from a gate command | Are gate-to-source voltage, polarity, timing and thermal limits correct? |
| Lamp | Converts electrical energy mainly into light and heat | Is the correct voltage/current actually present at the lamp terminals? |
Use measurements that split the problem
| Step | Action | Record |
|---|---|---|
| 1. Define | State the expected behavior and operating condition | Command, load, supply and environmental state |
| 2. Make safe | Identify every source and stored-energy mechanism | Isolation boundary and verified safe state |
| 3. Inspect | Look for loose, burnt, corroded or mechanically blocked parts | Observed condition without assuming cause |
| 4. Divide | Test a middle boundary with an appropriate instrument | Expected range, measured value and reference points |
| 5. Narrow | Move upstream or downstream according to the result | The first failed transfer and all enabling conditions |
| 6. Confirm | Repair the cause and retest under representative load | Before/after evidence and protection operation |
Power balance at a stage
P_in = P_useful + P_loss + dE_stored/dt
During steady operation the stored-energy term may average near zero, but during startup, charging, braking or switching it matters. A stage can show input voltage yet fail under load because available power is limited or being dissipated elsewhere.
- P_in
- power entering the chosen boundary, W
- P_useful
- intended power leaving it, W
- P_loss
- heat and other unintended conversion, W
- E_stored
- energy temporarily stored in electric, magnetic, chemical or mechanical form, J
Example: a low-voltage fan is commanded on but does not rotate
First verify the supply at rest and while the command is active. Then verify converter output, the controller’s enable and the voltage across—not merely near—the switching device and motor. If rated voltage reaches the motor but current is near zero, suspect an open connection or winding. If current is excessive with no motion, disconnect safely and investigate a stall or winding fault. If voltage collapses only under load, move upstream to source, wiring, connector and protection impedance. The measured pattern chooses the next step.
For meter setup and a disciplined measurement sequence, use Using a Multimeter and a Diagnostic Sequence. To distinguish current paths from opens and shorts, review Series, Parallel, Open and Short Circuits.
One-minute questions
Questions to answer before you apply this lesson
What should I select or check first for Follow Energy Through an Electrical System?
Trace function before naming a failed component. Define the expected input and output of each stage. Find the first boundary where valid input exists but the expected output does not. Then test the enabling conditions and load before condemning that stage.
Which assumption can change the conclusion?
Circuit state, waveform, source impedance, ratings, temperature and protection topology match the equipment being analysed.
What can go wrong if I copy the example directly?
The map is not permission for live probing. Before opening equipment, identify all electrical, mechanical, thermal and stored-energy hazards.
How do I verify the result in the real system?
Check the exact manufacturer data, units and limits, then verify the result by calculation, measurement or a controlled acceptance test.
Sources and further reading
- Selection and Use of Work Practices — 29 CFR 1910.333U.S. Occupational Safety and Health Administration · 2026-10-13Primary regulatory source reviewed for de-energizing exposed live parts and the qualified-work exception framework.
- Isolation and Verification ProceduresU.S. Occupational Safety and Health Administration · 2026-10-13Reviewed for isolating energy sources, rendering stored energy safe and verifying de-energization.
- Energy Control Program: Stored Energy and VerificationU.S. Occupational Safety and Health Administration · 2026-10-13Reviewed for residual-energy control, reaccumulation checks and verification principles.