In many competitive evaluations of power converters, unit price is the number-one decision factor, while TCO (Total Cost of Ownership) analysis is applied in only a minority of cases. This means that most purchasing decisions are made without considering the costs that actually determine the long-term economic impact.

This article explains why unit price is a misleading indicator, which hidden costs are usually ignored, and how to apply a practical TCO analysis to your next supplier evaluation.

The iceberg model: what you don’t see is what costs most

The unit price of the converter is the tip of the iceberg: visible, easy to compare and apparently decisive. Beneath the surface, however, there are seven cost categories that in many cases exceed the purchase price by a factor of 3 to 10:

1. Cost of field failure. A converter failure on a train does not cost EUR 1,000 for the replacement unit. It costs between EUR 10,000 and 55,000 once you add vehicle downtime (EUR 1,500–5,000/day), technician call-out (EUR 2,000–8,000), urgent shipping of the spare (EUR 500–3,000), root-cause investigation (EUR 5,000–15,000) and contractual service penalties.
2. Integration engineering. Changing supplier is not simply swapping one unit for another. It involves requalification, EMC testing, mechanical integration and documentation updates. Typical cost: EUR 30,000–75,000 per model.
3. Life-cycle support. A supplier offering 5 years of product availability for a vehicle with a 30-year service life is not saving you money: it is creating an obsolescence problem that will cost more than EUR 50,000 per model when the product is discontinued.
4. Warranty and after-sales costs. More restrictive warranty terms (1 year versus 5 years) and longer response times translate into higher operating costs.
5. Logistics costs. Lead times of 16 weeks from Asia versus 4 weeks from Europe. Higher safety-stock costs. Risk of delays from sea freight, customs and supply-chain disruption.
6. Training and documentation costs. A supplier providing documentation in English, Spanish and German reduces training costs for maintenance staff.
7. Supply risk. The 2021–2023 supply-chain crisis showed that dependence on distant suppliers can stall projects for 6–12 months.

How to calculate TCO: a practical framework

Calculating TCO does not have to be complex. For a practical evaluation, use this simplified formula:

Where:

• NRE is the non-recurring engineering cost (integration, qualification, documentation).
• The failure rate is derived from the equipment MTBF.
• The cost per failure includes all direct and indirect costs.
• The obsolescence cost is the redesign required when the product is discontinued.
• The logistics delta is the difference in inventory and transport costs between suppliers.

Example: when the cheapest converter costs twice as much

Consider two quotations for a railway DC/DC converter in a 200-unit project with a 25-year service life:

Supplier B looks 31% cheaper. But when TCO is calculated, Supplier B’s real MTBF (adjusted to MIL-HDBK-217F at 40 °C) is approximately 25,000 hours, which means 4 times more field failures. The total cost of failures over 25 years is 3–5 times the unit-price saving. In addition, Supplier B will require at least 3 obsolescence redesigns over 25 years (cost: EUR 90,000+).

Five questions for your next procurement process

Build these questions into every power-electronics supplier evaluation:

1. Give me the MTBF according to MIL-HDBK-217F at 40 °C ambient. If the supplier cannot or will not, ask yourself why.
2. What is your written commitment on spare-part and product availability? Accept only contractual commitments, not verbal ones.
3. What is your obsolescence management plan? When a key component reaches end of life, what is the process and who bears the cost of the redesign?
4. What is your real lead time and where do you manufacture? If the project cannot absorb a 4-week transport delay, you need European manufacturing.
5. Give me a TCO breakdown, not just the unit price. The suppliers who can do this, and are willing to, are the ones worth having as partners.

These five questions will steer your supplier list towards companies that deliver long-term value, not just short-term savings. To go deeper into how reliability is designed in to reduce TCO, see our white paper on reliability in critical power electronics.

Want to apply a TCO analysis to your next supplier evaluation? Our technical team can help you quantify the hidden costs.