Isolated vs non-isolated DC/DC for fuel cell systems

Published 2026-09-18 · 6 min read · Beijing Hypart Technology

Choosing between an isolated and a non-isolated DC/DC converter is one of the first architectural decisions in a fuel cell power system, and it is usually made too late — after the stack output voltage and the cooling design have already locked in.

What isolation actually does

An isolated converter separates the stack side from the downstream DC bus with a transformer barrier. The non-isolated topology has a direct conductive path between them. That single difference cascades into three practical outcomes.

1. Insulation failure path

This is the one that matters most in hydrogen. In a non-isolated system, the stack's negative terminal, the DC bus negative and — through the coolant loop or a mounting point — parts of the chassis can sit at similar potentials. A single insulation fault can place stack voltage on the cooling circuit. Isolated designs remove that path by construction.

2. Cost and mass

Isolation requires a transformer or resonant stage. That adds copper, core material, volume and loss. In a 2 kW forklift drivetrain this overhead can be a meaningful fraction of the system. Non-isolated designs are therefore common and sensible in low-power, well-enclosed, low-consequence applications.

3. Common-mode and system behaviour

Isolation also changes how much of the stack's common-mode voltage reaches the bus, which affects cable sizing, creepage requirements and the EMC design of the downstream inverter. For rail and marine applications governed by EN 50121, this is usually the deciding factor.

Where isolation is effectively mandatory

• Outdoor or mobile deployment with conductive coolant paths
• Systems where a coolant leak can reach energised parts
• Rail, road and maritime applications with formal EMC requirements
• Any installation where personnel have routine physical access

Where non-isolated is defensible

• Forklifts and indoor material handling
• Stationary generation in a controlled enclosure
• Lower power bands where isolation overhead dominates the BOM

How to specify it

Specify the converter on the stack's actual voltage window, including startup and dynamic transient behaviour — not just the nominal value. Then specify the isolation requirement explicitly: withstand voltage, insulation resistance and whether the barrier must be reinforced or basic. Leave these as "engineer to confirm" in a first RFQ and you will receive quotations that differ by a factor of two in price for parts that are not equivalent.