5/45 Capacitor: What It Means, How It Works, and How to Choose the Right One

A 5/45 capacitor is generally a dual run capacitor with two capacitance values— 5 µF and 45 µF—integrated into one component . In HVAC equipment, the smaller section is commonly used for the condenser fan motor, while the larger section is typically used for the compressor. The capacitor’s voltage rating, tolerance, terminal configuration, physical dimensions, and application must also match the equipment requirements.

What Is a 5/45 Capacitor?

When you see a capacitor labeled 5/45 µF , 45/5 µF , or 5+45 µF , the notation generally describes a dual-capacitance motor-run capacitor , rather than a single 5 µF or 45 µF capacitor.

The component contains two electrically separate capacitor sections that share a common terminal. A typical dual run capacitor has three terminals:

• C — Common
• FAN — Fan motor connection
• HERM — Compressor connection

For a typical HVAC application, the 5 µF section is associated with the fan motor , while the 45 µF section is associated with the compressor . The exact application, however, should always be verified against the equipment schematic and capacitor specification.

The key point is that 5/45 does not mean 5 divided by 45 . It represents two capacitance values contained within the same dual capacitor.

What Do the 5 µF and 45 µF Values Mean?

Actual equipment requirements can vary, so the original equipment specification should take precedence over a generic application description.

How Does a 5/45 Capacitor Work?

A motor-run capacitor provides the appropriate phase relationship between current and voltage in an AC motor circuit. This helps the motor produce the torque and operating characteristics required by the application.

In an HVAC condenser, the two capacitor sections serve different motor circuits.

The 45 µF section is typically connected between C and HERM and supports the compressor motor.

The 5 µF section is typically connected between C and FAN and supports the condenser fan motor.

Because both capacitor sections are housed in a single component, manufacturers can simplify wiring and reduce the number of separate components required inside the equipment.

This is one reason dual run capacitors are widely encountered in air-conditioning and refrigeration equipment. Commercially available 5/45 µF capacitors are commonly specified for motor-run and HVAC applications, with examples available at both 370 VAC and 440 VAC ratings.

5/45 vs. 45/5 Capacitor: Are They Different?

In most dual-capacitor applications, 5/45 and 45/5 describe the same two capacitance values.

The order in which manufacturers print the values can vary. What matters is the actual electrical specification and the terminal labeling.

For example:

• 5/45 µF
• 45/5 µF
• 5+45 µF
• 45+5 µF

can all describe a dual capacitor containing 5 µF and 45 µF sections .

However, you should not select a replacement based on the printed numbers alone. The voltage rating, tolerance, terminal configuration, physical dimensions, temperature rating, and equipment requirements also need to be checked.

Common Specifications to Compare

The capacitance value alone is not enough to identify a suitable replacement.

How to Read a 5/45 Capacitor Label

Suppose a capacitor is marked:

5/45 µF ±5%, 440 VAC, 50/60 Hz

The basic interpretation is:

• 5 µF: one capacitor section
• 45 µF: second capacitor section
• ±5%: capacitance tolerance
• 440 VAC: rated AC voltage
• 50/60 Hz: intended operating frequency

The terminals may then be marked C, FAN, and HERM .

A 5/45 µF 440 VAC dual capacitor is commercially available in HVAC/motor-run configurations, while similar 5/45 µF products are also available with a 370 VAC rating.

Do not assume that a higher voltage rating automatically makes any capacitor a suitable replacement. The replacement still needs to meet the equipment manufacturer's requirements and physical/electrical specifications.

5/45 Capacitor vs. Single 45 µF Capacitor

These two components are not automatically interchangeable.

A single 45 µF capacitor provides one capacitance section.

A 5/45 µF dual capacitor provides two sections:

5 µF + 45 µF

If the equipment requires both the compressor and fan capacitor sections, replacing the dual capacitor with a single 45 µF component would eliminate the separate 5 µF section.

Conversely, a dual capacitor may sometimes be used where only one section is required, but compatibility and the equipment manufacturer's wiring requirements must be verified before making such a substitution.

How to Test a 5/45 Capacitor

A dual run capacitor can be evaluated by measuring its individual sections.

After following the appropriate electrical safety procedures and isolating the capacitor from the circuit, measurements are typically made between:

• C and HERM → 45 µF section
• C and FAN → 5 µF section

The measured values should be compared with the capacitor's specified tolerance. For example, a ±5% specification means the acceptable range is determined from the nominal capacitance and the stated tolerance.

For a nominal 45 µF ±5% section:

45 × 5% = 2.25 µF

So the theoretical tolerance range is:

42.75–47.25 µF

For a 5 µF ±5% section:

5 × 5% = 0.25 µF

So the theoretical range is:

4.75–5.25 µF

Actual testing procedures should follow the meter manufacturer's instructions and appropriate electrical safety practices.

Common Mistakes When Choosing a 5/45 Capacitor

Mistake 1: Looking Only at the 5/45 Rating

A 5/45 µF designation does not provide the complete specification.

You should also verify:

Capacitance → Voltage → Tolerance → Terminals → Dimensions → Temperature → Application

Mistake 2: Confusing µF With Voltage

µF (microfarads) describes capacitance.

VAC describes the capacitor's voltage rating.

They are different electrical parameters and should not be substituted for one another.

Mistake 3: Assuming 370 VAC and 440 VAC Are Identical

Both ratings are used in motor-run capacitor products, but the appropriate rating depends on the equipment and replacement requirements. Commercial examples exist in both 370 VAC and 440 VAC configurations.

Mistake 4: Ignoring Terminal Markings

A dual capacitor is not simply a component with three interchangeable terminals.

C, FAN, and HERM have different electrical functions.

Always follow the equipment wiring diagram and the capacitor markings.

Mistake 5: Selecting a Replacement Only Because It Physically Fits

A capacitor can have the correct shape and still have an incorrect electrical specification.

For reliable equipment operation, electrical compatibility should be confirmed before physical compatibility .

Why Capacitor Selection Matters in PCB and PCBA Design

Although a 5/45 µF dual run capacitor is primarily associated with AC motor and HVAC applications , capacitors more broadly are fundamental components in electronic systems.

PCB designers may encounter capacitors in applications including:

• Power supply filtering
• DC/DC converters
• Motor control
• Industrial control systems
• HVAC control boards
• Inverters
• Automotive electronics
• Communication equipment
• Energy management systems
• Consumer electronics

The selection criteria change significantly depending on whether the capacitor is being used for motor operation, DC-link energy storage, filtering, decoupling, snubbing, timing, or signal conditioning .

For PCB applications, engineers also need to consider ESR, ESL, ripple current, dielectric characteristics, temperature behavior, voltage derating, package size, and placement rather than looking only at nominal capacitance.

This distinction is particularly important when moving from a component-level specification to a complete PCBA design.

Practical Selection Checklist for a 5/45 Capacitor

Before specifying or replacing a 5/45 capacitor, check the following:

1. Confirm the capacitance: Is the required value actually 5/45 µF?
2. Check the voltage rating: Verify the required VAC rating.
3. Check tolerance: Confirm whether the application requires ±5%, ±6%, ±10%, or another tolerance.
4. Verify terminal configuration: Confirm C, FAN, and HERM connections.
5. Check physical dimensions: Make sure the component fits the available space.
6. Verify temperature requirements: Consider the actual operating environment.
7. Check the application: Confirm that the capacitor is intended for the relevant motor/equipment type.
8. Compare the datasheet: Do not rely solely on a product title or visual appearance.
9. For PCB/PCBA projects: Evaluate the capacitor together with the complete electrical and thermal design.

PCBMASTER's Perspective on Capacitor Selection in PCBA Manufacturing

For electronic products that incorporate capacitors, component selection is only one part of the manufacturing process. The component must also be compatible with the PCB layout, BOM, assembly process, electrical requirements, thermal environment, and testing strategy .

PCBMASTER provides PCB, PCBA, and SMT manufacturing services for projects ranging from prototypes to larger-scale production. Its engineering support includes free engineering file review , helping identify potential manufacturability and design issues before production.

For complex electronic assemblies, this type of engineering review can be useful when capacitor specifications, package selection, PCB footprints, polarity requirements, spacing, or assembly constraints need to be checked before manufacturing.

PCBMASTER also supports customized PCB solutions including multilayer PCB , HDI , FPC , rigid-flex , high-frequency PCB , and metal-core PCB , allowing capacitor-related circuits to be manufactured within different electrical and mechanical requirements.

Its quality system includes ISO 9001, IATF 16949, UL, and RoHS certifications , while PCB and PCBA production includes inspection and testing procedures before shipment.

Frequently Asked Questions

Is a 5/45 capacitor the same as a 45/5 capacitor?

Generally, yes. Both designations can indicate a dual capacitor containing 5 µF and 45 µF sections . Always verify the actual label and terminal configuration.

What does 5/45 mean on a capacitor?

It normally means that the component contains two capacitance values: 5 µF and 45 µF .

Which side is 5 µF on a 5/45 capacitor?

In a typical HVAC dual run capacitor, 5 µF is associated with the FAN terminal , while 45 µF is associated with HERM. Verify the specific capacitor markings and equipment schematic.

Can I replace a 5/45 capacitor with a 45/5 capacitor?

If the two components have the same required capacitance values and otherwise compatible specifications, the reversed order of the printed values generally does not itself make them different. The terminal markings and equipment requirements must still be matched.

What voltage does a 5/45 capacitor use?

There is no single universal voltage. Commercial 5/45 µF motor-run capacitors are available in ratings such as 370 VAC and 440 VAC . The correct rating depends on the equipment specification.

Is a 5/45 capacitor polarized?

Typical AC motor-run dual capacitors are non-polarized components. Their terminals are identified by circuit function rather than positive and negative polarity.

Can a 5/45 capacitor be used on a PCB?

It depends on the application. A 5/45 µF dual motor-run capacitor is generally designed for motor/HVAC applications rather than ordinary low-voltage PCB decoupling. PCB capacitor selection should be based on the circuit's electrical, mechanical, thermal, and safety requirements.

Conclusion

A 5/45 capacitor is best understood as a dual-capacitance capacitor containing 5 µF and 45 µF sections , commonly used in AC motor and HVAC applications. The two values normally serve different motor circuits, with the larger capacitance commonly associated with the compressor and the smaller value with the fan.

However, 5/45 µF is only one part of the specification . Voltage rating, tolerance, terminal configuration, physical dimensions, temperature rating, and application requirements all need to be verified before selecting a replacement.

For PCB and PCBA engineers, the broader lesson is equally important: component selection should be evaluated as part of the complete electrical and manufacturing system , not simply by matching one number printed on the component.

Tags: #5/45Capacitor #Capacitor #DualRunCapacitor #HVACCapacitor #MotorCapacitor #PCB #PCBA #SMT #Electronics #PCBMASTER #ElectronicsEngineering

About the Author

Carol Luo

PCB Design Engineer

I'm Carol, a PCB Engineer at PCBMASTER with experience in PCB design and manufacturing engineering since 2018. I focus on translating engineering requirements into reliable PCB solutions, with expertise in stack-up design, material selection, and design-for-manufacturing (DFM). I share practical engineering insights from real-world PCB design and production experience.

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