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Technical Material
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 inuence 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 lm 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.
Cautions for Use of a Cooling Fan in the Vicinity of a Power Switching Circuit (prevention of electrolytic corrosion)
・Relocate fans far from all electromagnetic noise sources.
・Attach an EMC guard to ordinary fans. This should have an effect on electromagnetic noise due to radiation.
・As a power supply, the fan is wired from a circuit for which noise is not superimposed.
・Against heavy electromagnetic noise (electromagnetic induction) and conductive noise from the power supply line for a fan, we recommend the use of
an "Electrolytic corrosion proof fan" with ceramic bearing.
This cooling fan prevents electrolytic corrosion of bearings even under conditions where electromagnetic noise is generated.
Electrolytic corrosion of ball bearings is prevented by using ceramic balls in ball bearings. The ceramic material is an insulating material.
Manufacturable to meet specifications of all San Ace series fans.
■Component Diagram
Fans without anti-corrosion features installed near components that
generate electromagnetic noise, such as inverter controllers, are
liable to experience electrolytic corrosion.
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.
Range in which electrolytic
corrosion is generated
Level of noise induced by a fan
Distance from the noise source to the fan
Range in which electrolytic
corrosion is not generated
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
(1)
High-frequency electricity ows 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 ows 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 lter
(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 nger guard inside the fan. In each case, grounding to the cabinet is required.
Note2:Filter
Insert a common mode lter when the high-frequency electricity is superimposed on both lines "a" and "b" in the same phase and, if not, insert a normal mode lter.
http://www.sanyodenki.co.jp/product/newfan/indexf.html
(1)The fan gets charged with high-frequency electricity by high-frequency noise (electric eld/magnetic
eld) generated in the switching circuit.
(2)
Because of high-frequency electricity charged in the fan, an electric current ows 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 airow).
(6)
Countermeasure 2: To use a fan with ceramic bearings.
Switching circuit board of the equipment
Power supply for the fan
0Vterminal b
Circuit board grounding
Fan cabinet
Metal cabinet of the equipment
Component parts of
the switching circuit
e
Wind
+ terminal a
Electric field/magnetic field of
the high-frequency electricity
Pattern 1
Shielding metal
Pattern 2
Mounting
screw
High-frequency electricity is superimposed
onto the power line for the fan.
Return path of the high-frequency electricity
Propeller
(Grounding to the cabinet)
Occurrence of electrolytic corrosion Pattern 1
Occurrence of electrolytic corrosion Pattern 2
UPS, inverter, rectier, high-voltage power supply, etc.
Measures against electrolytic corrosion ACDC
A Case of electrolytic corrosion ACDC
Caution
Electrolytic Corrosion Proof Fan has been designed
to prevent the electrolytic corrosion of ball bearings
in the fan, but this does not guarantee that the fan
will operate normally under conditions where there
is strong electromagnetic noise.
Please be sure to fully evaluate the value of fan
malfunction due to noise in advance.
Impeller
Stator
Magnet
Coil
Bearing: Ball Bearing
(Material of ball: Ceramic)