Discover how a 1 farad capacitor powers RTC backup, MCU hold-up, and pulse loads. Includes energy formulas, ESR specs, PCB layout tips, and manufacturer table.

Most engineers spend their careers working in the microfarad range — 100 µF here, 470 µF there. Then a project comes along that needs to keep a microcontroller alive through a 500ms power interruption, or provide a burst of current to a GPS module during acquisition, and suddenly a 1 farad capacitor enters the conversation. That number stops people. One full farad. Not microfarads. Not millifarads. A farad — the same unit that defines the base SI measure of capacitance, and a value that would have required a capacitor the size of a car using conventional electrolytic technology just decades ago.

Today, a 1F supercapacitor fits in a package roughly the size of a AA battery, costs under two dollars in quantity, and opens the door to a category of energy storage that sits between conventional capacitors and rechargeable batteries. Understanding where this component fits — and where it doesn’t — is what separates designs that work from ones that look good on paper and fall apart in the field.

What Is a 1 Farad Capacitor and How Does It Differ from Regular Capacitors?

A 1 farad capacitor is not simply a scaled-up electrolytic. It belongs to a fundamentally different component family: the electrochemical double-layer capacitor (EDLC), also called a supercapacitor or ultracapacitor. The operating principle is different, the energy storage mechanism is different, and the design implications are different.

In a conventional aluminum electrolytic capacitor, charge is stored in a thin aluminum oxide dielectric layer. In a supercapacitor, there is no dielectric in the traditional sense. Instead, charge accumulates at the interface between a high-surface-area electrode (typically activated carbon) and an electrolyte solution — an effect called electrostatic double-layer capacitance. Because the electrode surface area is measured in hundreds to thousands of square meters per gram, capacitance values that would be physically impossible with dielectric technology become routine.

Supercapacitor vs. Battery vs. Electrolytic Capacitor

Property	Electrolytic Cap	1F Supercapacitor	Li-Ion Battery
Capacitance	µF range	1F – 3000F	N/A (Wh rated)
Energy Density	Very low	Medium-low	High
Power Density	Very high	High	Medium
Charge/Discharge Cycles	Unlimited	100,000 – 1,000,000+	300 – 2,000
Charge Time	Microseconds	Seconds to minutes	Minutes to hours
Self-Discharge	Negligible	Moderate (weeks)	Low (months)
Voltage Range	Fixed (stable)	Varies with charge state	Relatively flat
Temperature Range	–40°C to +105°C	–40°C to +65/85°C	–20°C to +60°C
Cost per Farad	High	Very low	N/A

The key insight is that supercapacitors don’t replace batteries and they don’t replace bypass capacitors. They occupy a specific niche: applications that need energy delivery over seconds or minutes, with very long cycle life and the ability to charge and discharge repeatedly without degradation.

Key Specifications of a 1 Farad Supercapacitor

When you open the datasheet for a 1F supercapacitor, the numbers you need to understand are quite different from what you’d look at for a standard electrolytic. Here’s what actually matters in a real design:

Parameter	Typical Value (1F EDLC)	Engineering Notes
Rated Capacitance	1.0 F ±20%	Measured at low frequency, DC bias applied
Rated Voltage	2.5V – 5.5V	Most common: 2.7V, 5.0V, 5.5V
ESR (DC internal resistance)	80 – 400 mΩ	Limits peak current delivery
Max Continuous Current	0.5 – 2.0 A	Thermal limitation
Leakage Current	1 – 10 µA	After 30 min at rated voltage
Operating Temperature	–40°C to +65°C or +85°C	Affects capacity and ESR
Shelf Life	10 years (stored uncharged)	Stored at recommended voltage
Cycle Life	> 500,000 cycles	At rated conditions
Physical Size	Ø8–16mm coin / radial	Voltage rating affects size significantly

Voltage Rating: The Most Critical Parameter

Unlike a battery that maintains a relatively flat voltage during discharge, a supercapacitor’s terminal voltage is directly proportional to its state of charge. A 1F capacitor charged to 2.7V that discharges to 1.35V has delivered exactly half its stored energy. This is not optional knowledge — it fundamentally determines whether your circuit will function throughout the discharge cycle.

The stored energy in a 1 farad capacitor at rated voltage is:

E = ½ × C × V²

At 2.7V: E = ½ × 1 × 2.7² = 3.645 joules

At 5.5V (series pair or higher-rated device): E = ½ × 1 × 5.5² = 15.1 joules

And the usable energy — from V_max to V_min — is:

E_usable = ½ × C × (V_max² – V_min²)

If your circuit requires minimum 1.8V and you start at 2.7V:

E_usable = ½ × 1 × (2.7² – 1.8²) = ½ × (7.29 – 3.24) = 2.025 joules

These joule-level energy figures put 1F supercapacitors in a clear application space: short-duration backup, pulse energy delivery, and real-time clock (RTC) maintenance — not multi-minute holdups or sustained load supply.

Practical Applications of the 1 Farad Capacitor

Real-Time Clock and SRAM Backup

This is probably the single most common application of a 1F supercapacitor in commercial electronics. Many microcontrollers and processors have an RTC subsystem and battery-backed SRAM that draws only 1–10 µA when the main supply is removed. A 1F capacitor at 3V can supply 1 µA for:

t = C × ΔV / I = 1 × (3.0 – 1.8) / 0.000001 = 1,200,000 seconds ≈ 13.9 days

That’s nearly two weeks of RTC backup from a single 1F supercapacitor, with no battery to replace, no disposal concerns, and essentially unlimited cycle life. This is why you see supercapacitors replacing coin cells in industrial controllers, smart meters, and building automation equipment where maintenance access is limited.

Microcontroller Hold-Up During Power Interruption

A microcontroller performing a write to non-volatile memory at the moment of power loss can corrupt data or lose critical state. A 1F supercapacitor, pre-charged to the rail voltage, can power a low-power MCU (drawing say 5–20 mA at 3.3V) long enough to complete the write and shut down gracefully:

At 10 mA load, from 3.3V to 2.0V:

t = C × ΔV / I = 1 × 1.3 / 0.010 = 130 seconds

That’s over two minutes — far more than the 50–500 ms that most graceful shutdown routines require.

Pulse Power for Wireless Transmission

GSM, LoRa, and other wireless modules can demand peak currents of 1–2A during transmission bursts, far exceeding what a coin cell or thin battery can supply without heavy voltage droop. A 1F supercapacitor in parallel with the power source absorbs these transients and provides the burst current locally, allowing a smaller, cheaper primary supply to run the system between transmissions.

Energy Harvesting Buffer

In solar and thermoelectric harvesting systems that generate irregular, low-average-power energy, a 1F supercapacitor can buffer the harvested energy and release it in controlled bursts when the application needs it. The unlimited cycle life is especially valuable here — a solar-powered sensor node that charges and discharges its energy buffer thousands of times per year would destroy a lithium battery in months but leaves a supercapacitor unaffected after years of operation.

Automotive and Industrial Memory Backup

In automotive EEPROM, instrument cluster, and infotainment systems, supercapacitors maintain voltage to memory circuits during ignition switch-off transients. The 1F value is common in lower-power systems; larger modules use stacked or higher-capacitance devices.

PCB Design Considerations for 1F Supercapacitors

Placing a capacitor on a PCB that stores joules rather than millijoules demands a different level of design care. Here’s what experienced engineers pay attention to:

Inrush Current Limiting

When you first apply power to a discharged supercapacitor, it looks like a near short-circuit. The initial charge current is limited only by ESR and the impedance of your source. A 1F cap with 200 mΩ ESR connected to a 5V rail can draw 25A instantaneously. This will trip current-limited supplies, damage thin PCB traces, and stress the source.

The solution is a series inrush limiting resistor — typically 10–100Ω — during initial charge. Once charged, this resistor can be bypassed with a FET or left in circuit if the IR drop is acceptable for your application. Purpose-built supercapacitor charger ICs (like the Texas Instruments TPS61225 or Maxim MAX38888) handle this automatically with controlled current ramp-up.

Polarity and Voltage Clamping

Supercapacitors are polarized. Reversing polarity, even briefly, can permanently damage the device. On a PCB where reverse polarity events are possible (automotive environments, field-replaceable modules), a protection diode or FET-based protection circuit is not optional.

Additionally, do not exceed the rated voltage. A 2.7V-rated device connected to a 3.3V rail without a voltage clamp will degrade rapidly. A simple Zener or a dedicated voltage clamp circuit keeps the supercapacitor within its safe operating area.

Self-Discharge and Leakage

Supercapacitors have significantly higher self-discharge than batteries. A charged 1F supercapacitor left on the shelf loses charge over days to weeks, depending on temperature and the specific device. For backup applications where the device may sit charged but unused for months, validate the leakage current specification against your minimum required voltage at end of standby period.

Layout and Thermal Placement

Keep the supercapacitor away from hot components. Elevated temperature accelerates aging and increases leakage current. ESR also increases at low temperatures, reducing peak current capability — important for cold-start automotive applications.

Popular 1 Farad Supercapacitor Series and Manufacturers

Series	Manufacturer	Voltage	ESR	Temp Range	Form Factor
BCAP0001	Maxwell (now Vishay)	2.7V	180 mΩ	–40 to +65°C	Radial
HVC0810-2R7105	Elna	2.7V	200 mΩ	–40 to +70°C	Radial
CPX3225A105	Murata	5.5V	120 Ω (coin)	–20 to +70°C	SMD Coin
SCMT22C105	Vishay	5.5V	60 Ω (coin)	–40 to +85°C	SMD Coin
FG0H105ZF	Panasonic (Gold Cap)	5.5V	50 Ω	–25 to +70°C	Radial
FS0H105ZF	Panasonic (Gold Cap)	5.5V	35 Ω	–25 to +70°C	Radial
SCP Series	Seiko (Seiko Instruments)	5.5V	150 Ω	–25 to +70°C	SMD Coin

Note: Coin-cell style supercapacitors tend to have higher ESR (ohm range) and are optimized for ultra-low current backup applications. Radial through-hole devices have much lower ESR and handle pulse currents far better. Choose based on your current requirements, not just capacitance.

Useful Resources for Engineers

Vishay (Maxwell) Supercapacitor Product Page https://www.vishay.com/en/capacitors/supercapacitors/ Includes BCAP series datasheets, application notes on charge balancing and inrush limiting.

Panasonic Gold Cap (EDLC) Lineup https://industrial.panasonic.com/ww/products/capacitors/edlc Full parametric selector for coin-type and radial EDLC devices with downloadable datasheets.

Murata Supercapacitor Products https://www.murata.com/en-us/products/capacitor/supercapacitor SMD coin-type devices optimized for RTC backup on compact PCBs.

Texas Instruments Supercapacitor Charger ICs https://www.ti.com/power-management/battery-chargers/supercapacitor-chargers/overview.html Application notes covering inrush limiting, balancing, and voltage regulation for supercapacitor systems.

Elna America EDLC Series https://www.elna-america.com/capacitors/double-layer/ Radial and SMD supercapacitors with application notes covering backup time calculations.

IEC 62391-1 — Fixed electric double-layer capacitors for use in electronic equipment. The governing international standard for supercapacitor testing and characterization.

CAP-XX Supercapacitor Design Guide https://cap-xx.com/resources/ Application notes on sizing, pulse power design, and energy harvesting with supercapacitors.

5 FAQs About the 1 Farad Capacitor

Q1: Can I use a 1F supercapacitor to replace a coin cell battery? For very low-current applications like RTC backup drawing under 5 µA, a 1F supercapacitor can replace a CR2032 for applications where the main power is available regularly enough to recharge it. The supercapacitor will not match a coin cell’s multi-year standalone backup capability, but if power is cycled at least monthly, it typically maintains enough charge to bridge power interruptions indefinitely. The big advantage is zero battery disposal concerns and essentially unlimited cycle life.

Q2: What happens if I charge a 1F supercapacitor to more than its rated voltage? The device will not fail immediately, but electrolytic decomposition begins above the rated voltage, generating gas inside the sealed housing. This causes physical swelling, accelerated ESR increase, and ultimately seal failure or case rupture. Even 100–200mV above rated voltage significantly shortens service life. Always use a regulated charge circuit with a voltage clamp set at or below the rated voltage.

Q3: Can I connect two 1F supercapacitors in series to get a higher voltage rating? Yes, and this is a common technique to achieve 5.4V or 5.5V from two 2.7V-rated cells. However, you must add a cell balancing circuit (either passive resistors or active balancing ICs) to prevent voltage imbalance between the cells. Without balancing, manufacturing variation in leakage current causes one cell to charge above its rated voltage while the other sits undercharged, damaging the overstressed cell over time.

Q4: How do I measure how much charge is left in a 1F supercapacitor? Unlike a battery where voltage is relatively flat across the discharge curve, a supercapacitor’s voltage directly indicates its state of charge. If you know V_max (charged) and V_min (discharged cutoff), and you measure the current terminal voltage, you can calculate remaining energy using E = ½ × C × V². This makes supercapacitor fuel gauging considerably simpler than battery state-of-charge estimation.

Q5: Why does my 1F supercapacitor feel warm during charging? Is it failing? Some warmth during rapid charging is normal — it’s I²R heating in the ESR. For a 100mΩ ESR device charging at 1A, that’s 100mW of dissipation. If the device becomes uncomfortably hot (above roughly 50°C case temperature), either the charge current is too high for the device’s ripple current rating, the ambient temperature is too elevated, or the ESR has degraded indicating an aging or damaged device. Check charge current against the datasheet maximum and consider a slower charge rate or higher-rated device.

Putting the 1 Farad Capacitor in Perspective

The 1 farad capacitor is not a drop-in replacement for anything you already have in your design toolkit. It’s a new tool with a specific job description: bridging the gap between capacitors and batteries for applications that need seconds to minutes of stored energy, with cycle life that makes lithium chemistry look short-lived by comparison.

Sized correctly, charged properly, and protected against overvoltage and polarity reversal, a 1F supercapacitor sitting on a well-designed PCB will quietly do its job for the life of the product — outlasting the microcontrollers it protects, the connectors it’s mounted near, and in many cases, the product itself. That’s a component worth understanding thoroughly before you put it in a design.