What to check and how often, when to change the electrolyte, and whether a rising voltage is normal. Decommissioning and storage have their own chapter.
- DailyLeaks · noise · smell · readings
- ElectrolyteNo fixed interval · by condition
- Stack serviceReturn it; we replace the MEA only
How to read this chapter
First timeStart with the daily, weekly and monthly lists and copy them into your own check sheet. Reading performance trends becomes useful a few months in.
Done this beforeGo straight to reading performance trends and deciding when to change the electrolyte.
On this pageThe intervals are guidance, not rules
The intervals are guidance, not rules
The check lists
Daily, or each shift
- No leaks, wetness, mist or splashing around the tubing, fittings and front-panel connections.
- No wetness or white crystals on or under the base of the unit. If you see any, stop operating and find the leak. Leaked electrolyte that dries out leaves KOH that can form a conductive path and melt nearby parts.
- No abnormal noise, vibration or smell.
- The front-panel LED and the app show normal operation with no active critical alarm.
- Stack current and voltage are reasonable for the setpoint.
- Electrolyte level, flow and temperature are within range.
- The discharge area is clear and ventilated, with no ignition source nearby.
Weekly
- Look back at the stack voltage at comparable operating points.
- Check that level, flow and temperature stayed stable.
- Look for alarms that keep recurring, and their pattern.
- Inspect hoses and fittings for wear, discolouration, crystal residue and small weeping leaks.
- Inspect cable routing and connectors for abrasion, looseness and overheating marks.
- Confirm the tubing supports are not loading the fittings and ports.
Monthly
- Check the electrolyte for discolouration and solids.
- Inspect the vent and drain paths for blockage, corrosion and salt build-up, and clean as needed.
- Clean the ventilation openings and the area around them so dust does not accumulate.
- Update the maintenance record: running hours, electrolyte change dates, alarms, observations and corrective actions.
Maintenance log
The unit logs operating data, but not electrolyte concentration and changes, the water used, leaks or anything done by hand. Keeping these columns lets us narrow down a cause quickly when something goes wrong. Write one line at every check.
| Column | What to write | Example |
|---|---|---|
| Date | Day of the check | 2026-10-05 |
| Total run hours | The value on the control app Home screen | 312 h |
| Operating point | Current, electrolyte temperature, pressure | 50 A · 50 °C · 10 barg |
| Stack voltage | Measured at the same operating point. This column is for the trend | 41.2 V |
| Electrolyte | Whether it was changed, the measured concentration and method, colour and foam | Not changed · 0.10 M (refractometer) · clear |
| Feed water | Quality (conductivity) and the day the reservoir was refilled | 0.8 µS/cm · refilled |
| Leaks and crystals | Base of the unit, ports and fittings, vent ends | None |
| Alarms | Alarms raised since the last check and how often | Electrolyte flowrate low ×1 |
| Action taken | Anything done by hand, such as cleaning, part replacement or a setting change | Cleaned fan filter |
| Checked by | Who did the check | (signature) |
Changing the electrolyte
Best practice: measure conductivity regularly
When the KOH concentration falls, the electrolyte's conductivity falls with it. Measuring conductivity regularly therefore tells you the state of the electrolyte before the voltage starts to rise. A conductivity meter is all it takes.
- When
- Measure once right after filling fresh electrolyte and record it as your baseline. After that, measure once a month.
- How
- Stop electrolysis and let it cool, put on PPE, and draw a small sample from the DRAIN port into an alkali-resistant container. Read the 25 °C value on a temperature-compensated conductivity meter. At a different temperature the same electrolyte reads differently.
- Reference
- 0.1 M KOH reads about 20–23 mS/cm at 25 °C. Comparing with your own baseline is more reliable than the absolute value.
- More than 20% below baseline
- Replace the electrolyte and look for the cause under Where electrolyte escapes below. Leave the cause in place and the fresh electrolyte will go the same way.
- More than 20% above baseline
- Water is short and the electrolyte has concentrated. Check first that water make-up is working. See Water make-up in the Operation and control chapter.
If you cannot measure conductivity
Replace the electrolyte if you see any of the following. You will find out later than by measuring conductivity, so we recommend getting a conductivity meter where possible.
- Voltage creeps up at the same operating point
- The electrolyte concentration may have fallen. It looks like stack degradation, but voltage often recovers with fresh electrolyte alone. Measure the concentration before suspecting the stack.
- Make-up interval or level behaves differently
- If make-up runs more or less often than usual at the same operating point, electrolyte is escaping somewhere or water is short. Compare with the make-up entries in your maintenance log.
- Moisture at H2 OUT tests alkaline
- During steady operation, touch pH paper to the moisture coming out of H2 OUT. If it tests alkaline, electrolyte is crossing to the hydrogen side. Replace the electrolyte and contact us.
- Restarting after a long idle period
- While idle, carbon dioxide from the air can dissolve and weaken the electrolyte. If you cannot measure it, replace it before restarting.
- Heavy foaming
- Electrolyte is carried out through O2 OUT with the foam, so concentration and level both fluctuate. Replace it and watch whether the foam returns. If it does, contact us.
- Discoloured or with solids
- It is contaminated or something has dissolved into it. Replace it, photograph the drained electrolyte and contact us.
- After fixing a leak or replacing parts
- While it leaked, KOH escaped and make-up water took its place, so the concentration is already low. Replace all of it once the repair is done.
Where electrolyte escapes
In normal operation the KOH does not decrease. If the concentration falls anyway, KOH is escaping somewhere and the make-up pump is replacing the loss with pure water. There are three ways out.
| Where | How you can tell |
|---|---|
| Out of the stack | A seal between cells is leaking. The stack perimeter or the base of the unit gets wet or grows white crystals. A small leak may never trip the leak sensor and show only as a slow fall in concentration. |
| Inside the stack, across to the hydrogen side | Electrolyte crosses the membrane from the oxygen side (anode) to the hydrogen side (cathode) and leaves with the hydrogen. Moisture from H2 OUT tests alkaline on pH paper. A fast depressurisation after pressurised operation can give briefly alkaline moisture, so check during steady operation. |
| From the electrolyte tank | The tank gasket, a joint or a connecting fitting is leaking. The base of the unit gets wet or the electrolyte leak alarm appears. The tank sits inside the enclosure, so unless you are qualified, do not open it; contact us. |
In every case, contact us rather than just replacing the electrolyte again and again. Leaks from the stack are handled through stack service.
Cleaning
Exterior
- Wipe with a cloth dampened with clean water. Never spray liquid onto the system.
- If needed, use ethanol on painted and metal surfaces only, applied to the cloth, avoiding labels and seams.
- KOH residue shows up as white crystals: dissolve it with a water-dampened cloth and wipe again with clean water.
- Do not clean during operation. Stop the system first, especially before wiping near the ventilation openings, connectors or front-panel fluid connections.
Interior
Reading the performance trend
Stack voltage creeps up over time, from electrode and membrane degradation and from operating history. The question is not whether it rises but how.
- Can be normal
- A slow, steady rise over a long period
- Worth investigating
- A step change at constant current, a large rise or fall over a short period, especially with the stack or electrolyte temperature climbing too, and large fluctuations at constant current
When it looks wrong, look outside first
- Whether the electrolyte condition or concentration has drifted
- The DI water quality and any source of contamination
- Whether flow and temperature are stable and cooling is working
- The hydrogen and oxygen routing, backpressure, and anywhere gas gets trapped
- The sensors and analysers, and the wiring and connections
If it persists after those checks, contact us with the operating history and the trends you recorded.
Decommissioning and storage
What this chapter is based on
- HXB-V1 datasheetPDF · 2.1 MB
- HXB-V1 outline drawingPDF · 1.9 MB
- HXB-V1 user manualOn request
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.