A controller fan losing airflow rarely warns you on day one. The electronics run a few degrees above normal, the robot keeps producing and everything looks fine. The problem shows up weeks later: an overtemperature trip during the afternoon heat peak, or an intermittent drive fault that comes and goes with no pattern. Catching a degraded fan in time is one of the cheapest, most cost-effective jobs in a preventive plan.
Which fans are in a controller and what they cool
In any ABB (IRC5, OmniCore), KUKA (KRC4, KRC5) or FANUC (R-30iA/iB) cabinet there are several ventilation groups with different jobs, and they don't all fail the same way:
- Cabinet extraction fan: moves the general air inside the enclosure. Its failure raises internal ambient temperature and affects everything equally.
- Drive/servo amplifier heatsink fan: the critical one. It cools the power electronics directly. Its failure trips drive overtemperature alarms relatively quickly.
- Power supply / DC bus fan: less common, but its failure causes erratic behaviour in the power supply.
The key point is that many of these fans have no speed feedback. The system doesn't know whether they spin at 3,000 rpm or 800: it only reacts once the temperature sensor has already risen. That's why failure is caught earlier by inspection than by alarms.
Symptoms of a dying fan
Ordered by what you'll notice first on the floor:
- New noise: low hum, rattle or the squeal of a dry bearing. It's the first sign, almost always weeks before total failure.
- Weak airflow: put your hand at the extraction grille and the air comes out weak or too warm.
- Cabinet hotter than usual: opening the door you feel more heat than in twin robots in the same cell.
- Intermittent overtemperature alarms: they appear during the hottest hours and clear on their own as things cool. By this point you're already late.
- Fan that starts with a delay or won't start cold: typical of worn bearings; hard to overcome inertia.
Careful: don't mistake a stopped fan for a clogged filter. The thermal symptoms are identical, but the fix (and the cost) aren't. Before ordering a fan, always check the filter.
How to check it, in order
- Log a reference temperature. With identical robots running, compare the internal cabinet temperature of the suspect with a healthy twin. A gap of 8-10 °C is a clear signal. If you have drive temperature readings in the system, use them.
- Visual and audible inspection with the robot running. Locate each fan and confirm they all spin. A stopped fan is obvious; one spinning slowly isn't. Listen for bearings.
- Check the air intake filter. If it's clogged with dust, grease or chips, the fan may be perfect and the problem is airflow. Clean or replace the filter and measure again.
- Airflow test. With a clean filter, confirm air comes out strongly at the extraction. A thin strip of paper works to see the draft.
- Removed fan condition. With the controller powered down and discharged, spin the blades by hand: no rubbing, axial play or noise. Check the blades aren't caked with dust (it unbalances them and accelerates wear).
Working inside a robot cabinet means respecting lockout/tagout and waiting for the DC bus capacitors to discharge, as they hold dangerous voltage for minutes after cutting power. If you're not clear on the procedure, don't open it: call in corrective maintenance.
Clean or replace?
The practical rule:
- Clean if the fan spins free, with no bearing noise and no play: blow out the blades, clean the grilles and change the filter. Restores airflow at no spare cost.
- Replace if there's bearing noise, delayed start, axial play, or airflow stays low after cleaning. A fan bearing that's starting to fail won't recover; it only gets worse.
The fan is a cheap spare compared with a drive burnt out from running hot. As soon as you detect bearing noise, schedule the swap; don't wait for total failure. Check availability at spares and exchange: for older generations it's worth keeping one in stock.
Beware the wrong fan
Not all cabinet fans are the same in voltage, size or airflow. Fitting a lower-airflow one "because it fit" is a common mistake that permanently under-cools the electronics and is hard to diagnose. Respect the original specs.
Recommended intervals
As a general industry guide, not a manufacturer rule:
- Fan inspection and filter cleaning: every 3-6 months in clean environments; monthly in foundry, cutting, welding or dusty/greasy environments.
- Preventive fan replacement: worth considering above a high band of service hours, especially if it has ever made noise. Many shops replace them at the major annual overhaul of robots running 3 shifts.
Building these checks into your preventive maintenance plan prevents 90% of heat trips. If the robot is already tripping overtemperature repeatedly, review the other causes in our article on thermal management and ventilation.
When to call a specialist
- If after cleaning filters and confirming the fans spin, the temperature stays high: there may be an internal cooling or sensor problem.
- If the overtemperature trip appears with the electronics objectively cold: suspect a sensor or the control board.
- If you're not trained to work inside the cabinet with the DC bus charged.
A €30 fan nobody looked at is one of the most frequent causes of damage to drives costing a hundred times more. It's the perfect example of why preventive maintenance pays off.