HydroXpandHandbook

← HXS-30 handbook

Quick start

HXS-30 · updated 2026-10-05

Nine steps: the BoP you need, the ports and line sizes, the electrolyte loop and hydrogen line, filling, the DC connection, the current ramp and first-run checks.

The sequence from the stack in place to your first hydrogen, in nine steps.

The HXS-30 is a 46-cell, 30 kW stack. You build the rectifier, electrolyte circulation, cooling, gas handling, instrumentation and interlocks around it. The connection specification is in the datasheet, and if you send us your system conditions we will agree the interface with you.

  • PrerequisiteAn external BoP and a DC supply
  • Rated input80 V · 360 A
  • Recommended condition0.1 M KOH · 50 °C
  • PPEEye protection · alkali-resistant gloves
How to read this chapter

First timeWork through the nine steps in order. This is a bare stack, so the BoP has to exist first. Step 1 lists what you need.

Done this beforeRe-check the ports and the loop, then jump to the first run. The operating range and the shutdown sequence are in the operation and shutdown chapter.

On this page1. What you need in place

1. What you need in place#

  • 1 × DC power supplyThe rated operating point is 80 V at 360 A. Stack voltage rises during operation, so we recommend a supply able to deliver up to about 92 V. If you plan to run up to the stack voltage limit (2.2 V per cell, 101.2 V), choose a supply that reaches it. It needs a constant-current mode.
  • Electrolyte circulation and temperature controlA tank, a circulation pump, a heat exchanger and cooling, all in KOH-compatible materials. Size the cooling from the heat table in the operation chapter, for the highest voltage you will keep running to.
  • Gas-liquid separation and purificationGas-liquid separation after the hydrogen outlet, and drying or purification equipment for the purity you need.
  • Pressure and safety systemsUp to 10 barg on the hydrogen side, with the anode at atmospheric pressure. Provide pressure protection, detection, interlocks and an emergency stop to suit.
  • Electrolyte and DI waterFor the first fill, 0.1 M KOH in DI water; for make-up during operation, DI water.

Photos show the type of item only.

HXS-30: what goes around itCirculation, water treatment, instrumentation, drying, compression and storage

2. Identify the ports#

Find the labels on the stack and confirm the four connections below. Naming can vary by revision, so follow the labels on the unit you received.

Front and side line drawings of HXS-30. On the end plate with the ports: upper left, oxygen and electrolyte out (1-inch double ferrule, gas and liquid together); upper right, hydrogen out (3/4-inch double ferrule); lower centre, electrolyte in (1-inch double ferrule). Two M12 tapped holes on top of the end plate are the lifting points; you supply the eyebolts. The side view shows a length of 400 mm and a height of 570 mm including the terminals; the two plates sticking up are the M10 DC terminals and are not lifting points. Lift at four eyebolts (two per plate) or by forklift on the pallet.
Figure 3-1 HXS-30 ports, DC terminals and lifting points. The front view uses coordinates from the end-plate 3D model; the side view simplifies the cell stack. They can differ between revisions, so follow the labels on your stack.
ConnectionWhat passes throughFitting
Electrolyte inletElectrolyte in1-inch double ferrule
Oxygen and electrolyte outletOxygen and electrolyte out, together1-inch double ferrule
Hydrogen outletHydrogen out3/4-inch double ferrule
DC terminalsDC power inM10

3. Connect the electrolyte loop#

A typical arrangement leaves the tank and comes back to it.

  • Tank → pump → heat exchanger → electrolyte inlet → oxygen and electrolyte outlet → tank
Schematic of the HXS-30 electrolyte loop and hydrogen line. Electrolyte leaves the tank, passes a circulation pump set below the tank level and a heat exchanger, and enters the electrolyte inlet at the bottom of the stack. From the oxygen and electrolyte outlet at the upper left it returns to the tank, kept at 1 inch with no big climb and fall; the oxygen vent on the tank goes to its own safe discharge point. The hydrogen outlet at the upper right (3/4 inch) goes to a safe discharge or approved downstream equipment. Recommended flow is 40 L/min, and the hydrogen line and oxygen vent are never joined.
Figure 3-2 HXS-30 electrolyte loop and hydrogen line. Schematic; instruments, valves and interlocks are omitted.
  1. Connect the tank outlet to the circulation pump inlet.
    • Place the pump below the tank liquid level. With the suction side always flooded, it does not draw in air.
    • Do not use the pump to pressurise the anode loop. The anode side runs at atmospheric pressure.
  2. Connect the pump outlet through the heat exchanger to the stack's electrolyte inlet.
  3. Return the oxygen and electrolyte outlet to the tank.
    • The return has to flow smoothly. A line that climbs and falls traps gas and interrupts the return.
    • Do not neck the return line down below the port size (1 inch).

4. Connect the hydrogen line#

  1. Connect a 3/4-inch line to the hydrogen outlet.
  2. Route the hydrogen outlet to a safe, well-ventilated discharge point, or to approved downstream equipment.
    • Downstream you need gas-liquid separation: moisture leaves with the hydrogen.

5. Fill the electrolyte#

Before filling, check the loop connections and the tightness of the fittings again.

  1. Make up 0.1 M KOH in DI water.
    • KOH of 95% purity or better, and water to ASTM D1193 Type II (1.0 µS/cm or below at 25 °C) recommended. The maximum is 30 µS/cm.
  2. Fill the tank to a level that suits your circulation loop.
    • CheckThere is no leakage at the fittings and ports.
    • If notIf anything leaks, stop circulation and retighten that fitting.
  3. Run the circulation to purge air from the loop and the stack, then top the tank back up.

6. Set flow and temperature#

  1. Start circulation and confirm the flow is stable.
    • CheckFlow settles near the recommended 40 L/min. A brief wobble at first while air clears is normal.
    • If notIf it keeps fluctuating or will not rise, check that the pump suction is flooded and no gas is trapped in the return line.
  2. Control the electrolyte temperature to 50 °C.

7. Connect the DC supply#

  1. Connect supply + to stack + and supply − to stack −.
    • Size the cables and lugs for 360 A continuous.
  2. Tighten the M10 terminals securely.
    • Confirm the tightening torque with us on delivery. Over-torque damages the terminal; under-torque overheats the joint.
  3. Verify the polarity again before switching on.
    • If notIf it is reversed, do not apply current; reconnect it correctly.

8. Start the first run#

  1. Confirm circulation is running and flow and temperature are stable before applying current.
  2. Set the DC supply to constant current.
  3. Ramp the current in steps up to the rated 360 A.
    • At each step, confirm flow, temperature control and voltage response are normal before moving to the next.
    • Heat rises with current. Check that the cooling keeps up.
    • CheckAt each step the voltage rises then settles, and flow and temperature hold. The first-run measurement was about 76 V at 360 A.
    • If notIf the voltage approaches 101.2 V (2.2 V per cell) or you see a leak or a temperature problem, take the current to 0 A and see Troubleshooting.

9. First-run checks#

Once at rated current and after a short hold, confirm three things.

  • No electrolyte leaking at the stack ports, the fittings or the cell edges, by eye.
  • The electrolyte flow and temperature are stable.
  • Stack voltage rises sensibly with current. The first-run measurement in the datasheet is about 76 V for the stack at 362 A (1.660 V per cell).

What to record#

Once the first run is stable, write that day's values down once. It becomes the starting point when you read the voltage trend later.

ItemWhat to write down
IdentificationModel and serial number, from the label
Operating pointStack current and voltage, electrolyte flow and inlet and outlet temperatures, at the operating point you have chosen
Cell voltagesIf you can measure them, the individual cell voltages and the spread between the highest and the lowest
If instrumentedHydrogen flow and pressure, hydrogen purity, hydrogen in oxygen
Electrolyte and waterMake-up date and concentration, feed-water quality
Operation and shutdownWhat to watch in normal operation, and how to stopMaintenance: reading the performance trendHow to read this record over time

What this chapter is based on

Resource library →

TroubleshootingA find-by-symptom table, the order of checks, the causes behind odd voltage behaviour, and what to send us.
Was this page helpful?

Ask the engineer who built it

If your case is not covered here, send us the operating condition and what you observed. The engineer who designed the system answers directly.

Technical enquiry