Inductor Network Combiner

Build a series, parallel or mixed inductor network and read the equivalent inductance live. Set the supply current and the table gives you each inductor’s share of the current, its flux linkage and the energy stored in its magnetic field.

Inductor network

L1FIRST
L2
L3

Supply currentA

Equivalent inductance

L_eq =6.97 mH2 groups · inductor rules match resistors (series add, parallel reciprocal)

The one reactive component that follows the resistor rules

Inductors in series add, and inductors in parallel combine by reciprocal sum — identical to resistors, and the opposite of capacitors. If you can do resistor networks you can already do these. The catch is elsewhere: inductors couple to each other through their magnetic fields, and the formulas above quietly assume they do not.

Energy lives in the magnetic field

A capacitor stores energy in an electric field as ½CV²; an inductor stores it in a magnetic field as ½LI². That is why the table above is driven by a current rather than a voltage — current is the state variable for an inductor, the way voltage is for a capacitor. It is also why interrupting an inductor’s current produces a large voltage spike: the field has to dump its energy somewhere.

Mutual inductance breaks the simple rules

Two inductors close enough to share flux add or subtract a mutual term M = k√(L₁L₂), so the series total becomes L₁ + L₂ ± 2M — plus if the fields aid, minus if they oppose. The combiner assumes no coupling, which is the right assumption for shielded parts or ones mounted at right angles, and the wrong one for two coils side by side on the same axis.

Learn more → Inductors — Learn

Quick experiments

Confirm series inductors just add. Two 10 mH inductors in series give 20 mH. No reciprocals, no surprises — inductors behave like resistors here, which makes them the easy case after capacitors.
Halve it in parallel. Switch the second to parallel and the total drops to 5 mH, below the smaller member. Two equal inductors in parallel always give half, mirroring two equal resistors.
Watch energy scale with the square of current. Double the supply current and look at the energy column. Each entry goes up four times, not two, because W = ½LI². This is why an inductor's saturation current matters far more than its resistance.
See current divide in inverse proportion. Put 1 mH in parallel with 10 mH. The smaller inductor takes most of the current, because it presents less opposition to a change in current — the same inverse split as parallel resistors.
Compare flux linkage across a series chain. In series every inductor carries the same current, so flux linkage Ψ = LI is proportional to inductance alone. Set three different values and the table shows the largest inductor holding the most flux — and the most energy.

Formula reference

Inductors in series: $L_{total} = L_1 + L_2 + \cdots + L_n$
Same rule as resistors — assuming no coupling.
Inductors in parallel: $\frac{1}{L_{total}} = \frac{1}{L_1} + \frac{1}{L_2} + \cdots + \frac{1}{L_n}$
Always smaller than the smallest member.
Energy stored: $W = \tfrac{1}{2} L I^2$
In the magnetic field. Quadruples when current doubles.
Flux linkage: $\Psi = L I$
In webers. The magnetic analogue of charge.
Induced voltage: $v = L \frac{di}{dt}$
Why interrupting inductor current makes a spike.
Mutual inductance in series: $L_{total} = L_1 + L_2 \pm 2M, \quad M = k\sqrt{L_1 L_2}$
Plus when the fields aid, minus when they oppose.

Symbol	Meaning	Unit
$L_{total}$	Equivalent inductance	H
$I$	Current through the inductor	A
$W$	Energy stored in the field	J
$M$	Mutual inductance between two coils	H
$k$	Coupling coefficient, 0 to 1	—

Common mistakes

Applying the capacitor rules to inductors.
Inductors follow the resistor rules: series adds, parallel reciprocates. Capacitors are the odd one out, not inductors. Mixing them up gives an answer that is wrong in the obvious direction.
Ignoring mutual coupling between nearby inductors.
Two coils sharing flux add a ±2M term to the series total, which can shift the result substantially. The simple formula only holds for parts that are shielded, spaced, or mounted at right angles to each other.
Treating inductance as constant regardless of current.
A ferrite-cored inductor saturates: past its rated current the core stops responding and inductance collapses, often abruptly. Datasheets quote a saturation current for exactly this reason, and it is usually the limiting spec.
Forgetting the winding resistance.
Every inductor has series DC resistance, and in a power path that DCR causes real loss and heating. Two inductors in parallel halve the inductance but also halve the DCR, which is sometimes the actual reason for doing it.
Switching an inductor's current off abruptly.
v = L di/dt means a fast interruption produces a very large reverse voltage — enough to destroy the switching transistor. Relay and motor drivers need a flyback diode across the coil to give that energy somewhere to go.

Frequently asked questions

How do inductors combine in series and parallel?

Exactly like resistors: series inductances add, and parallel ones combine by reciprocal sum. Inductors are the reactive component that follows the familiar rules, and capacitors are the odd one out.

How much energy does an inductor store?

Half times inductance times current squared. Because the current is squared, doubling it quadruples the stored energy, which is why saturation current is usually the limiting specification on a power inductor.

What is mutual inductance and when does it matter?

When two coils share magnetic flux, a mutual term M equal to k times the square root of L1 times L2 is added or subtracted, so a series pair becomes L1 plus L2 plus or minus 2M. It matters whenever inductors sit close together on the same axis, and can be ignored for shielded parts or coils mounted at right angles.

What is flux linkage?

Inductance multiplied by current, measured in webers. It is the magnetic analogue of charge on a capacitor, and in a series chain it is proportional to inductance alone because every inductor carries the same current.

Why does switching off an inductor create a voltage spike?

Because the induced voltage is inductance times the rate of change of current. Interrupting the current abruptly makes that rate enormous, so the voltage can reach hundreds of volts. A flyback diode across the coil gives the stored energy a path and protects the switching device.