Your Power Supply Is Part of the Anode System

In When the Anode Is Not the Problem, we wrote about current distribution, scaling, and wiring mistakes that get blamed on coating. This piece covers the part nobody opens: what sits between the mains and the cell.

Most titanium anode complaints start the same way: "coating failed", "voltage jumped", "life shorter than quoted". When we ask for the rectifier datasheet, sometimes the answer is "just a standard 0–40 V supply". That sentence explains more field failures than any coating batch.

MMO titanium anodes are dimensionally stable, but they are not indifferent to what you push through them. The coating cares about current density, reversal events, dry start, and how dirty the DC really is.

Ripple matters-but it is not the only killer.​ Switched-mode supplies with high ripple do age coatings faster through repeated micro-cycles of over-current and relaxation. Published data shows MMO coatings have reasonable immunity to AC ripple at moderate levels (under 5% ripple typically adds only millivolts of cell-voltage variation), so a unit running at 3–5% ripple is not automatically doomed. Problems start when ripple climbs into the double digits, or when it combines with over-current, poor flow, and operator error. We have seen "14-month failures" blamed on ripple that were actually dry-start events nobody logged. Treat ripple as one variable in a stack, not the headline cause.

Polarity reversal is worse than people think.​ DSA anodes are built to evolve chlorine or oxygen, not to sit as a cathode. If a control fault reverses polarity for even a few seconds, chlorine-side coatings can hydrate, gas differently, lose adhesion, and the titanium substrate may see hydrogen evolution it was never designed for. Some plants survive one event. Many do not. This is not a coating issue. It is a protection relay that was never installed.

Dry start is the quiet killer.​ Someone opens the isolating valve later than the current setpoint. Plates are in air, current flows, titanium base heats, coating cracks before the first litre of brine arrives. No coating survives "electricity before electrolyte". MMO tolerates short air exposure during maintenance-not a controlled energizing sequence with no liquid. If your system does not have a flow switch interlocked to the rectifier, this will happen. Ask your system integrator for the wiring diagram.

Acid wash, then power on-wrong order.​ Operator finishes HCl circulation, closes acid line, forgets rinse, hits start. Residual acid film plus high current density etches the active layer from the edges. The anode did not "wear out naturally". The sequence wore it out.

What to do about it.​ Treat the power supply as part of the anode system, not a separate line item. Confirm ripple (under 5% is a reasonable target), confirm interlock between flow switch and rectifier, confirm polarity protection, and confirm startup sequence in the control logic-request this documentation from your system integrator if you are not building the skid yourself. A coating life commitment comes with operating boundaries: current density, temperature, salinity, and power quality. Move any one of them, and the life number moves with it.

Buyers spec the anode to the gram of precious metal. Then they hang it on a rectifier nobody reviewed. In the field, the anode is only as good as the current you push through it.