Solid-State Relay Total Cost of Ownership

The purpose of the Total Cost of Ownership (TCO) calculator is to help engineers make an informed, data-driven decision when selecting a power-switching solution.

While solid-state relays and power controllers often have a higher initial purchase price than electromechanical relays, they can be significantly more cost-effective over time when factors such as operating frequency, service life, downtime, and warranty-related service costs are taken into account. The TCO calculator allows users to compare these variables directly by evaluating the long-term cost of each solution within the context of a specific application.

Although HBControls designs and manufactures solid-state switching solutions, the intent of the calculator is not to force a particular outcome. Instead, it is meant to provide transparency and help users determine which technology—electromechanical or solid-state—offers the lowest overall cost and highest reliability for their operating conditions.

In some applications, an electromechanical relay may still be the most appropriate choice. The TCO calculator exists to make that determination clear, based on usage and real-world operating costs rather than upfront price alone.

The calculations used in the Total Cost of Ownership (TCO) calculator are based on straightforward, well-established math. The purpose of the calculator is not to introduce complex modeling, but to apply consistent, transparent calculations across real-world operating variables such as relay life expectancy, switching frequency, warranty exposure, and service costs.

The calculator has been used and validated internally and by customers over many years, and no calculation errors have been identified in its current form. Like any engineering tool, its accuracy ultimately depends on the accuracy of the data entered by the user. Assumptions such as operating cycles, duty patterns, and service costs will vary from one application to another.

The TCO calculator is intended as a decision-support tool—not a replacement for engineering judgment. If results appear inconsistent with expectations, or if you have questions about how the calculations are performed, HBControls encourages users to contact our technical support team so we can review the inputs and assumptions together.

An HBControls power controller is a solid-state relay that is already mounted to a properly sized, thermally efficient heat sink. Because the relay and heat sink are sold as a complete, pre-engineered assembly, the cost of the heat sink is already included in the price of the power controller.

The TCO calculator includes separate entry fields for solid-state relays and heat sinks to accommodate users who purchase those components individually and assemble them themselves. If you are using an HBControls power controller, simply enter the total cost of the assembly in the “SSR Cost” field and leave the “Heat Sink Cost” field set to $0.

This approach reflects the real-world purchasing and installation cost of a pre-assembled power controller and eliminates the need for additional thermal calculations or component pricing.

Unlike electromechanical relays, solid-state relays have no moving parts, so their life expectancy is not primarily determined by the number of switching operations. When properly mounted to an adequate heat sink and operated within their electrical and thermal limits, solid-state relays are typically specified by MTBF (Mean Time Between Failures) rather than by a fixed number of operations.

Translating MTBF into an equivalent “number of operations” is inherently imprecise because solid-state relay life is influenced more by thermal cycling than by switching frequency alone. Factors such as heat sink size, load current relative to rating, duty cycle, and ambient temperature all affect how much the internal temperature of the relay rises and falls during normal operation. Smaller thermal excursions generally correspond to longer service life, while larger excursions can reduce it.

Because there is no industry-wide standard for converting MTBF into an operations-based life expectancy, the TCO calculator uses a conservative, fixed value of 50 million operations for solid-state relays. This value represents the low end of observed real-world performance and helps ensure that comparisons against electromechanical relays remain realistic and fair.

The purpose of the TCO calculator is not to predict the exact end-of-life of a solid-state relay, but to provide a consistent baseline for comparing long-term cost and reliability between switching technologies under typical operating conditions.

The type of load has a direct impact on relay wear and long-term reliability, particularly for electromechanical relays.

Resistive loads are relatively benign. They produce minimal inrush current and little arcing when mechanical contacts open or close. Inductive loads store energy in a magnetic field, which attempts to maintain current flow when contacts open. This results in sustained arcing that accelerates contact erosion and shortens relay life.

Capacitive loads impact electromechanical relays differently but can be just as damaging. When contacts close, a capacitive load initially appears as a near short circuit, resulting in a very high inrush current. This sudden current surge can cause contact pitting, welding, or material transfer, especially if switching occurs near the peak of the AC sine wave. Repeated exposure to high inrush currents significantly reduces contact life, even when steady-state current is well within the relay’s rating.

The TCO calculator accounts for both inductive and capacitive load behavior by adjusting electromechanical relay life expectancy to reflect real-world operating conditions. This allows for a more accurate comparison between electromechanical and solid-state switching technologies over the life of the equipment.