RL current transient calculator

Ideal series RL current step at one time.

circuits-rl-transient.napkin / editable

SCENARIO COMPARISON

Compare the numbers.

This source describes an analytical model. Its quantities and checks are the view.

Scenario	timeConstants	currentA
	0.01	1.0376
	0.01	0.830078

All calculated quantities are listed with the inputs. Switch to Source to inspect the equations.

SCENARIOS / CALCULATED VALUESSAME SOURCE

Change an input to see the consequences.

current budget1.04 A✓ passes

BASELINE INPUTS

voltage12 Vresistance10 ohminductance100 mHtime20 ms

CALCULATED

timeConstant0.01 s

current1.0376 A

Edits change the baseline source.

THE SOURCE

Edits below update the same model.

# RL current transient
# Scope: Ideal series RL current step at one time.
# Status: illustrative worked example; engineering review pending.
# Inputs are example values. Checks are editable example requirements, not standards.

voltage = 12 V
resistance = 10 ohm
inductance = 100 mH
time = 20 ms

timeConstant := inductance/resistance [s]
current := voltage/resistance*(1-exp(-time/timeConstant)) [A]

check current budget: current <= 1.5 A

scenario alternative: voltage = 9.6 V

Calculated from your source · not saved

Baseline · Baseline

current budget1.04 A ✓ passes

alternative · alternative

current budget0.83 A ✓ passes

Illustrative first-order example. Checks are editable requirements, not design standards. The broader topic may require additional equations, data, and validation.

Formula and units

This example uses the following equations. Input names and units match the editable source above.

time constant: timeConstant = inductance/resistance [s]
current: current = voltage/resistance*(1-exp(-time/timeConstant)) [A]

Original worked example

These are the baseline values in the downloadable source. Edits above let you test your own values.

Given

voltage: 12 V
resistance: 10 ohm
inductance: 100 mH
time: 20 ms

Calculated

time constant: 0.01 s
current: 1.0376 A

Assumptions and limits

Ideal series RL current step at one time.

The requirement checks use the limits written in this example. Passing a check does not establish that the model covers every load, material behavior, or operating condition in a real design.

Download this .napkin example ↓

Take it further with your agent

Napkin keeps the inputs, equations, checks and assumptions together in one study. Your agent sets it up; you change the numbers.

Try with Claude ↗

codex 'Use Napkin (https://napkin.engineering/mcp, or the local Napkin plugin) to build a study: RL current transient. Inputs: resistance; inductance; source; initial current. Outputs: current rise/decay; stored energy. Model scope: Ideal or parameterized lumped components. Read napkin_capabilities and the current snapshot. Ask me for the values that matter, label assumptions with units, author .napkin source, validate it and apply it with napkin_source using the current revision, then open the study. Add checks for the limits I supply. Keep unsupported analyses explicit.'

Claude needs the Napkin connector; Codex needs the Napkin plugin. Set up your agent ↗

The broader study

The topic brief below describes the broader scope. The worked example above states the particular calculation it implements.

Inputs: resistance, inductance, source, initial current
Outputs: current rise/decay, stored energy
Modes: calculate, compare, sweep
Drawing: Schematic and waveform

EXECUTABLE WORKED EXAMPLE · FIRST-ORDER MODEL · CHECK THE SCOPE & ASSUMPTIONS