What a fuel cell stack expects from its balance of plant

Published 2026-10-25 · 4 min read · Beijing Hypart Technology

A fuel cell stack is a well-defined black box. It does not care how the system around it is organised — it presents four interfaces, and each one sets hard requirements on the balance of plant. Design against the interfaces and the integration gets much simpler.

Interface 1 — hydrogen in, hydrogen out

The anode side needs hydrogen supplied at stable pressure and recirculated so unreacted fuel is not wasted. In practice that means four parts: an explosion-proof circulation pump sized in slpm for the stack, a gas-liquid separator that strips water from the recirculated flow without venting hydrogen, a pressure transmitter qualified for hydrogen service, and a leak detector watching the enclosure — catalytic combustion sensing with a signal direct to the ECU is the common choice.

Interface 2 — air supply

The cathode side needs a metered, pressurised air stream. The compressor defines the pressure ratio; the mass air flow sensor tells the control system what is actually entering the stack. Meter the mass, not the volume — a hot-film sensor holds its reading when temperature and pressure move, which is exactly when a volumetric reading lies.

Interface 3 — the cooling loop

The coolant loop removes reaction heat, and it is also the most common path for an electrical fault. Keep the coolant below roughly 5 µS/cm with a conductivity sensor, filter particulates before they block channels, seal the loop with a sealless pump, and size the expansion tank for the coolant's thermal expansion — not just the steady-state heat load.

Interface 4 — the DC bus

The stack's voltage swings with load. The DC/DC converter turns that window into a stable bus voltage and, when isolated, removes the conductive path between the stack and everything downstream. Specify the converter on the stack's full voltage window including startup and transients — not the nominal voltage — and state the isolation requirement explicitly.

A selection checklist

• Hydrogen — recirculation flow (slpm), separator water capacity, leak detection range and output signal
• Air — pressure ratio, mass flow range, sensor accuracy over the operating window
• Cooling — conductivity target, filtration rating, pump head and flow at operating temperature
• Electrical — stack voltage window, bus voltage, isolation requirement, communication protocol

Every component family on this site maps to one of these four interfaces. Send us the stack data and we will propose a set that matches — catalogue models first, custom designs where the envelope demands them.