What Are Capacitors in Parallel?

Capacitors are connected in parallel when their corresponding terminals are connected to the same two circuit nodes.

        ┌──────||────── C1 ──────┐
        │                        │
+V ─────┼──────||────── C2 ──────┼──── GND
        │                        │
        └──────||────── C3 ──────┘

Unlike capacitors in series, capacitors connected in parallel have the same voltage across each capacitor.

V1 = V2 = V3 = Vtotal

Parallel Capacitance Formula

The equivalent capacitance of capacitors connected in parallel is the sum of their individual capacitances.

For capacitors, the formula is:

CT = C1 + C2 + C3 + ...

This means adding a capacitor in parallel always increases the total capacitance.

Parallel Capacitor Calculator

Example — Two 100 µF Capacitors in Parallel

Suppose two 100 µF capacitors are connected in parallel.

C1 = 100 µF

C2 = 100 µF

The equivalent capacitance is:

CT = 100 + 100

CT = 200 µF

Therefore, two identical 100 µF capacitors in parallel produce an equivalent capacitance of 200 µF.

Equal Capacitors in Parallel

When identical capacitors are connected in parallel:

CT = N × C

where N is the number of capacitors.

For example, four 100 µF capacitors connected in parallel produce:

CT = 4 × 100

CT = 400 µF

Voltage Across Parallel Capacitors

Every capacitor connected in parallel has the same voltage across it.

V1 = V2 = V3 = Vtotal

For example, if three capacitors are connected across a 24 V supply, each capacitor has 24 V across its terminals.

The voltage rating of every individual capacitor must therefore be suitable for the applied voltage.

Charge Stored by a Capacitor

The charge stored by a capacitor is calculated using:

Q = C × V

For a parallel capacitor bank, the total charge is:

QT = CT × V

The total charge is also equal to the sum of the charge stored by each individual capacitor:

QT = Q1 + Q2 + Q3 + ...

Parallel Capacitor Charge Calculator

Example — Charge Stored

Suppose a 100 µF capacitor is charged to 12 V.

Q = C × V

Q = 100 µF × 12 V

Q = 1200 µC

This is equal to:

Q = 1.2 mC

If another 100 µF capacitor is connected in parallel, the total capacitance becomes 200 µF and the total stored charge becomes 2.4 mC at the same voltage.

Energy Stored in Parallel Capacitors

The energy stored in a capacitor is:

E = ½CV²

For a parallel capacitor bank, use the equivalent capacitance:

ET = ½CTV²

The total energy is also equal to the sum of the energy stored in each individual capacitor.

Capacitor Energy Calculator

Increasing Power-Supply Filter Capacitance

Connecting capacitors in parallel is commonly used in power supplies when a larger total capacitance is required.

For example:

4700 µF + 4700 µF

= 9400 µF

The capacitors must have suitable voltage ratings and should be appropriate for the ripple current and operating temperature of the application.

Parallel Capacitors in Amplifier Power Supplies

Large electrolytic capacitors are frequently connected in parallel in audio amplifier and power-supply applications.

For example:

4 × 10,000 µF

CT = 40,000 µF

The parallel arrangement increases the total capacitance while all capacitors remain exposed to the same supply voltage.

When selecting capacitors for this type of application, voltage rating, ripple-current capability, ESR, temperature rating and physical mounting should be considered.

Capacitor Voltage Rating

Although capacitors in parallel have the same voltage, the voltage rating of each individual capacitor still matters.

If a capacitor is rated for 25 V, it should not be connected across a supply that exceeds its permitted operating voltage.

For reliable designs, an appropriate voltage margin should be used.

Polarized Capacitors in Parallel

Polarized capacitors such as aluminum electrolytic capacitors can be connected in parallel provided their polarity is respected.

+V ─── +| |− ───┐
                │
+V ─── +| |− ───┼── GND
                │
+V ─── +| |− ───┘

All positive terminals connect to the positive rail and all negative terminals connect to the negative rail.

Never reverse the polarity of a polarized electrolytic capacitor.

Capacitors With Different Values

Parallel capacitors do not need to have identical capacitance values. Their values simply add.

For example:

100 µF + 220 µF + 470 µF

CT = 790 µF

This can be useful when combining different capacitor values to obtain a desired total capacitance.

Capacitors With Different Voltage Ratings

Capacitors connected in parallel may have different voltage ratings, but every capacitor must have a voltage rating suitable for the actual voltage applied across the network.

The capacitor with the lowest voltage rating effectively limits the maximum safe operating voltage of the parallel bank.

Parallel Capacitors and Ripple Current

Connecting several capacitors in parallel can also distribute ripple current between the capacitors.

The actual current sharing depends on capacitor characteristics, including ESR and impedance.

For high-current power supplies, the manufacturer's ripple-current specifications should be checked.

Parallel Capacitors and ESR

Connecting capacitors in parallel can reduce the effective ESR of the capacitor bank.

This is one reason multiple electrolytic capacitors are often used instead of a single very large capacitor in power supplies.

The actual ESR depends on the capacitor construction, frequency, temperature and operating conditions.

Parallel vs Series Capacitors

Common Applications

• Power-supply filter capacitors
• Audio amplifier power supplies
• DC smoothing
• Energy storage
• Decoupling networks
• High-capacitance banks
• Ripple-current distribution
• Creating non-standard capacitance values

Common Mistakes

• Forgetting that every capacitor sees the full supply voltage.
• Using a capacitor with an insufficient voltage rating.
• Reversing the polarity of electrolytic capacitors.
• Ignoring ripple-current requirements.
• Ignoring capacitor temperature rating.
• Assuming all capacitors share ripple current equally.
• Ignoring ESR in high-current applications.

Key Points

• Parallel capacitances add directly.
• The voltage is the same across every parallel capacitor.
• Total charge is the sum of individual capacitor charges.
• Parallel capacitors increase total capacitance.
• Parallel capacitors can reduce the effective ESR of a capacitor bank.
• Every capacitor must have an appropriate voltage rating.
• Electrolytic capacitor polarity must be respected.
• Ripple current and temperature ratings should be checked in power applications.