When and how humidifiers would fail?

This Taiwanese made humidifier is perhaps the most common in use. If you are using such humidifiers for a year or two, it is prudent to do some preventive maintenance such as cleaning and oil its bearings. You will be surprise how dirty it can become!

















One that I have been using with a plastic cover to direct the mists sideways and prevent young birds falling in.




















Recently I noticed the motor didn't turn when the hygrostat controller indicator was "ON". The first thought came to mind was to check the hygrostat output control or relay. I used a 10Amp Omron relay with built-in an LED indicator - which is useful for visual check. Next I gave the fan with a little spin and the motor kicked into life. That helped to kick start it so too much frictions at the bearings I thought.

I took it home to do some cleaning and oil the moving parts. I have dismantled such unit several times before, so it is a familiar routine. A good exercise if you are doing it first time and discover its working principle.

Picture below is a dismantled unit turned upside down. I normally remove the metal 'squirrel' cage as it can be easily damaged. Beware of its sharp edges too!



















The tip of the spindle sucks water up a cone and spin outwards to the 'squirrel' cage. In the process kinetic energy of water increases and breaks into fine droplets as it hit the blades. The fan on top draws the water droplets upwards into a fine spray. Simple and very clever!















After removal of plastic housing, there are only two electrical parts: the motor and a capacitor.















Beneath the metal cap plate is rubber O-ring to prevent water sipping into the motor. It does add friction to the motor shaft - so I oiled both top and bottom rings.



















The top O-ring.



















& the bottom O-ring.




















The motor housing must be opened in order to reach the bearings. Below is a burned out motor & capacitor. The bearing is seen around the motor shaft. By now you will have many loose screws lying around and should keep track of them for re-assembly!















It worked fine as I put the unit back together - the problem fixed so I thought!
A week later, I noticed the same problem again! So I scratch my head - only 2 working parts, what can be wrong? The capacitor looks normal without any bulge. Common sense was to replace it and see what happens - BINGO! That was the problem - the starting capacitor!















Fortunate I detected sign of early failure. My lesson was I did not suspect the capacitor without any bulge - the sign of failing capacitor. Oiling the moving parts did help somewhat but gave a false impression the problem was fixed!

So the failure mode begins at the capacitor. Without sufficient starting torque, the motor stalls without cooling. Heat builds up gradually within the motor until its stator wire insulation breaks down creating short circuit and even melts wire! A failed unit (one shown above) I inspected had its plastic enclosure warped by the heat, pretty hot it must be!

It is very essential to have an external mains protective fuse or circuit breaker. I use a 20A circuit breaker to protect the power points in the bird house.