Test Cy is steady-state damp heat aimed at components, and its signature setting is 85 degrees at 85 percent relative humidity, the pairing the industry calls 85/85. Nothing swings. The chamber climbs to the condition, holds it dead steady, and stays there for the full duration, often 168, 500, 1000, or 2000 hours. The severity is the temperature, the humidity, and the clock together.
Steady is the whole idea.
A cyclic test works a part with change. Test Cy works it with constancy, soaking the component in unbroken heat and moisture until the slow, moisture-driven mechanisms have had time to run their course. For a capacitor, that steady soak is what drives water through the case and into the dielectric, where the damage hides.
A cyclic test works a part with change. This one works it with constancy, soaking the component until the slow damage has had time to run.
A capacitor that might take years to fail in a damp climate can be pushed there in weeks at eighty-five and eighty-five.
Severity in Test Cy is the run length as much as the condition.
A component spec names how many hours at 85/85 a part has to survive, and the choice climbs with how much confidence the maker needs. A 168-hour run is a quick screen. Five hundred hours is a common qualification step. A thousand or two thousand hours backs a claim of long life in a humid place. Capacitor programmes lean on the longer runs, since the moisture mechanisms in a small sealed part take time to reach the dielectric and do their work.
The hours are the test as much as the heat.
Two parts held at the same 85/85 can earn very different ratings on duration alone. The one that holds its numbers through 2000 hours carries a stronger claim than the one checked at 168, even though the air around them was the same.
Capacitors take moisture badly in ways many other parts shrug off, which is why Test Cy is aimed so squarely at them. A capacitor is, at heart, two conductors separated by a thin dielectric, and almost everything that ages it under heat and damp comes down to water reaching that dielectric or the joints around it. Different chemistries fail in different ways, and the test catches each. A ceramic part shows its trouble as a slow fall in insulation resistance and a creeping rise in leakage as moisture works into microcracks and along the metal terminations. An electrolytic part can dry out or, the reverse, take up water that attacks its foil and shifts its capacitance and its loss. A film capacitor can corrode at the sprayed-on end contacts where the foil meets the lead, raising resistance and nibbling at capacitance. In every case the damage is gradual and hidden, the kind that never trips a quick bench test but turns up as a part drifting out of tolerance a year or two into service, and steady eighty-five and eighty-five is the condition that draws it out in weeks. That is why a capacitor specification almost always names a damp-heat soak, and why the chamber that runs it has to hold the eighty-five-eighty-five point flat and unbroken for the whole length of the run, since any sag or swing changes how much water reaches the dielectric and so changes the verdict on the part.
Every capacitor family carries its own pass limits, and the test reads against them rather than against one universal bar. A ceramic part might allow only a small percentage shift in capacitance and set a hard floor on insulation resistance, since its job is often to hold a precise value in a tuned circuit. An electrolytic might tolerate a wider capacitance change while capping the ESR rise and the leakage current, because its failure mode is drying rather than drifting. A film part watches capacitance and dissipation factor closely, the two numbers that betray a wetted dielectric. The 85/85 soak is identical for all of them, and the limits applied at the end come from each part's own specification, so a generous limit and a tight one can both ride on a single run in the same chamber. That is the quiet economy of the method: one condition, one box, many parts judged each against the standard it was built to meet.
The point of 85/85 is acceleration.
A capacitor that might take years to absorb enough moisture to fail in a warm, damp climate can be pushed to the same state in weeks at 85 degrees and 85 percent. Models such as the Hallberg-Peck relation tie the chamber hours to field years, using the temperature and the humidity to set how much faster the clock runs inside the box. A 1000-hour pass at 85/85 stands in for a long stretch of real service.
The model is a guide rather than a promise. The acceleration depends on the part and the failure mechanism, so a lab treats the field-life figure as an estimate and leans on the measured drift and the failure count to judge a component.
Test Cy runs the parts unpowered. The capacitors sit in the heat and humidity with no voltage across them, so the test measures what moisture alone does to the part. Putting a voltage on the parts during the soak is a separate test, a biased humidity test that adds the electric field which drives ion migration and speeds certain failures. Cy keeps the two apart, so a maker can see the moisture effect on its own before deciding whether a biased run is needed as well.
The hard part for the chamber is endurance.
Holding 85 degrees and 85 percent humidity steady for a thousand or two thousand hours means the box runs for weeks without a break, and any drift over that span shifts the stress the parts feel. The humidity system has to top up its water and hold the wet-bulb steady the whole time, the heaters have to keep the temperature flat, and the controls have to ride out a building's day-and-night swings without letting the condition wander.
Water becomes a supply problem. A chamber running for weeks draws a steady flow of pure water, so it feeds from a deionized or reverse-osmosis source with enough reserve to last the run, and a drain clears the condensate without anyone opening the door.
Run length shapes how a lab plans its chambers. A 2000-hour test holds a box for almost three months, so a lab running long Cy soaks needs enough chambers to keep qualifications moving while one sits occupied. The economics push toward filling each run, which loops back to loading the chamber densely without spoiling the airflow, and toward keeping the box reliable enough to run the full stretch without a stoppage that would void the result.
A chamber that holds a condition for weeks has to stay calibrated through all of it. A humidity sensor that drifts halfway through a 1000-hour run quietly shifts the stress every part feels for the rest of the soak, and the result then rests on a condition that was never quite right. A lab calibrates the temperature and humidity sensors before a long run and trusts a chamber with a proven hold, since there is no second chance to rerun a soak that wandered after week three.
The chamber logs the condition through the whole soak, and that log is part of the result. A report that claims 1000 hours at 85/85 has to show the box held the condition for those hours, so the temperature and humidity trace travels with the electrical readings into the qualification record. A gap or an excursion in the log can put the whole run in question. A long Cy soak belongs on a chamber that records as steadily as it holds.
Component testing fills a chamber with many small specimens at once. A single Cy run might hold hundreds of capacitors on racks or boards, and the airflow has to reach every one so each sees the same 85/85. A part tucked in a dead spot or shadowed by its neighbours soaks at a different humidity and ages differently, so the racking spaces the parts and the fan carries the conditioned air through the whole load.
Uniformity across a packed load is the quiet challenge. The chamber holds a tight band in an empty working space, and a crowded tray can spoil that if the air cannot move, so a lab loads to the pattern the chamber allows rather than cramming in as many parts as will fit.
A steady damp heat soak wants moisture in the air and on the part as vapour rather than as liquid water. Drops of condensation on a component change the test, bridging terminals and pooling where the vapour alone would not gather. The chamber holds its walls and the load above the dew point, heats the space evenly, and steers clear of the cold spots where water would bead. The part stays damp, never wet.
A Cy result means little without a starting point.
Before the soak, the lab measures each part dry, often after a short bake to drive off any moisture it arrived with, so the before reading reflects the part itself and not the warehouse it sat in. Every later reading gets compared against that dry baseline, and the drift between them is the number that counts. Skip the baseline and a part that was already damp on arrival looks like it aged less than it did.
For a capacitor the headline numbers are insulation resistance and leakage current, and both move with moisture. As water tracks into the part, the insulation resistance falls and the leakage rises, sometimes by orders of magnitude on a part that is starting to fail. The standard sets when those readings are taken, and whether the part is measured warm at the end of the soak or after a recovery, since a reading taken while the part is still damp can differ sharply from one taken once it has dried out.
A capacitor rarely dies outright in 85/85. It drifts. Measurement comes before, sometimes during, and after the soak, and the part is judged on how far capacitance, leakage, insulation resistance, ESR, and dissipation factor have moved against the limits the spec allows. A part that still works but has drifted past its tolerance has failed as surely as one that shorted, and catching that drift is why the measurements carry as much weight as the soak itself.
Moisture does not all stay. When a part comes out of the chamber and dries, some of the drift it showed at the wet end reverses as the water leaves, while some stays on as permanent damage. That split is why the standard fixes the recovery time and the moment of the final reading. A measurement taken too late, after the part has fully dried and rebounded, can hide a moisture problem that would show under damp service, so the timing is set to catch the part in a telling state.
Some parts face a condition harder than 85/85.
Highly accelerated work pushes the temperature and humidity higher still, into the pressurised regime where water is forced in faster, to compress a long life into days instead of weeks. Test Cy holds the steady-state, ambient-pressure ground, the 85/85 that became the industry's common yardstick, and leaves the pressurised acceleration to the methods built for it. For a capacitor headed into ordinary humid service, the steady 85/85 soak is the measure that maps cleanly to the field.
Test Cy is the steady, component-level member of the damp heat family.
The cyclic methods swing temperature to drive condensation and breathing, and the composite ones add a freeze. Cy does none of that. It holds one steady, punishing condition for a long time, which suits the slow, diffusion-driven aging that moisture works on a small sealed part. When a maker needs to know how a capacitor will hold its value after years in a humid world, the steady 85/85 soak is the test that answers.
The damage in a steady damp soak is the slow arrival of water where it does not belong. Held at eighty-five degrees and eighty-five percent humidity, moisture diffuses through a capacitor's case and gathers at its dielectric and its seals over hundreds of hours, and each chemistry suffers in its own way. In a multilayer ceramic part, water along internal flaws lets ions migrate and drops the insulation resistance while leakage climbs. In a film capacitor, absorbed moisture shifts the dielectric and nudges the value off its mark. In an aluminium electrolytic, humidity attacks the seal and lets the electrolyte dry, which lifts the equivalent series resistance and shortens the life. The steady soak finds each because it gives the water the time it needs to reach the part.
The point of holding it steady is acceleration with a known relationship behind it.
Heat and moisture speed the reactions that age a component, and models such as the Hallberg-Peck relation tie the chamber hours to field years, using the temperature and the humidity to set how much faster the clock runs inside the box. A thousand hours at eighty-five and eighty-five stands in for a long stretch of humid service, so a part that holds its value, its leakage, and its insulation resistance through the soak carries a claim a maker can defend. The model guides the figure; the measured drift across the run confirms it.
Test Cy turns the slow damage of damp air into a result a lab can read in weeks. IEC 60068-2-67 holds a component at a steady 85 degrees and 85 percent humidity for hundreds or thousands of hours, long enough for moisture to work into a capacitor's dielectric, seal, or electrolyte and shift the numbers that define it. A chamber for the test holds that condition flat for the whole run, keeps pure water flowing, carries a packed load in even air, and stays free of condensation from the first hour to the last. Run that way, a Cy soak tells a maker whether a capacitor will still hold its value, its leakage, and its life after a long spell in a warm, wet climate.