Electrolytic Corrosion Proof Fan

Cautions for use of a cooling fan in the vicinity of a power switching circuit

If a fan is installed near a large-power or high-voltage switching circuit, the heavy electromagnetic noise resulting from electromagnetic induction in such circuits or the influence of high-frequency noise imposed through the power line of the fan may induce current through the shaft bearing of the fan.

Such current may damage the oil film on the bearing and even the friction surface of the bearing. This adverse effect is known as "electrolytic corrosion of the fan". Electrolytic corrosion affects the smooth revolution of the fan and may reduce its service life.

An audible symptom is unusual noise emitted from the fan.This adverse effect is often observed and may partly be explained by the practice of mounting high-density parts, which reduces the gap between the switching circuits and the fan and the use of higher switching frequencies apt to provoke induction. Data processing/communications devices that operate at low voltages are not liable to electrolytic corrosion since they generate less electromagnetic noise.

A Case of Electrolytic Corrosion

Fans without anti-corrosion features installed near components that generate electromagnetic noise, such as inverter controllers, are liable to experience electrolytic corrosion.

No. Use Period until the occurrence of unusual noise
1 Switching power supply 6 months to 2 years
2 UPS 6 months to 2 years
3 General-purpose inverter 1 to 1.5 years
4 Air cleaner 2 to 3 months
5 Inverter for LCDs 6 months

The curve shown in the graph below represents the relationship between the level of the electromagnetic noise induced by a fan and the distance from the fan to the noise source.

電磁ノイズ

Occurrence of electrolytic corrosion Pattern 1

1. The fan gets charged with high-frequency electricity by high-frequency noise (electric field/magnetic field) generated in the switching circuit.
2. Because of high-frequency electricity charged in the fan, an electric current flows through the bearing of the fan.
3. The electric current breaks the oil membrane on the surface of the bearing and the bearing gets abraded (electrolytically corroded).
4. This symptom often occurs in equipment in which switching circuits are sped up and implemented in high density.
5. Countermeasure 1: To provide a shield plate (Note 1) inside the fan (The plate should be such that does not interfere with air flow).
6. Countermeasure 2: To use a fan with ceramic bearings.

Occurrence of electrolytic corrosion Pattern 2

1. High-frequency electricity flows from the circuit board into the inside of the fan superimposed with the power line for the fan.
2. High-frequency electricity that has entered into the fan flows through the bearing.
3. Oil membrane on the surface of the bearing gets broken and the bearing gets abraded (electrolytically corroded).
4. Countermeasure 1: To remove high-frequency component between terminals "a" and "b", "a" and "e" and "b" and "e" of the power supply for the fan, or to insert a filter (Note 2) into the power line for the fan.
5. Countermeasure 2: To use a fan with ceramic bearings 
6. Cables should be twisted in order to decrease induction to the power line for the fan.
Note 1:Shielding metal plate
As an electromagnetic shield metal, "EMC Guard" is available from our company. Certain shielding effect can be expected from mounting a general-purpose finger guard inside the fan. In each case, grounding to the cabinet is required.
Note2:Filter
Insert a common mode filter when the high-frequency electricity is superimposed on both lines "a" and "b" in the same phase and, if not, insert a normal mode filter.
装置のスイッチング回路基板

Measures against Electrolytic Corrosion

(1) Relocate fans far from all electromagnetic noise sources.
(2) Use anti-corrosion fans equipped with ceramic bearings.
(3) Attach an EMC guard to ordinary fans.
(4) As a power supply, the fan is wired from a circuit for which noise is not superimposed.

※The EMC guard could be effective against electromagnetic noise caused by radiation, but against heavy electromagnetic noise (electromagnetic induction) and conductive noise from the power supply line for a fan, we recommend the use of an "anti-electrolytic corrosion fan" with ceramic bearing.

What is an EMC guard ?

It is a metallic piece that protects materials from the adverse effects of electromagnetic noise sources.It provides electromagnetic shielding. It is attached to the casing of a device by means of the fan fixing screw(s).Ground the devices equipped with an EMC guard.

EMC guard

EMC guard

attached to a cooling fan

attached to a cooling fan

EMC guards

Fan EMC guards
Dimensions
(mm)
Thickness
(mm)
Representative
model numbers
Ø172
Ø172×150
51 109L17***5** 109-1036
9GV57***5**
109E57***5**
109E17***5**
25 109E47***4**
□120 38 9GL12***1** 109-1037
9LB12***1**
109L12***1**
9G12***1**
25 9G12***4**
109P12***4**
□92 25 109L09***4** 109-1040
109P09***4**
□80 32 109P08***2** 109-1038
25 109L08***4**
109R08***4** 109-1039
9A08***4**
20 109P08***6** 109-1038
15 109L08***7** 109-1039

※Please inquire regarding EMC guards other than those listed.
EMC:Electro Magnetic Compatibility, or a capability of a system when its performance is not affected by an electromagnetic environment.
Solution (3) takes effect in ordinary cases.You can choose from among EMC guards of different sizes. Example: We chose solution (3) because the electromagnetic noise emitted by our UPS, which induces current up to the fan, is not excessive.
The ceramic material used for the bearing in solution (2) prevents current from flowing in it. Strong electromagnetic noise (electromagnetic induction) will not damage the bearing.So, we recommend solution (2) for an environment with heavy electromagnetic noise.