
3. INSTALLATION
B–63443EN/02
HARDWARE
10
The temperature of the air inside a cabinet rises due to heat generated in
the units and parts installed in the cabinet, compared with the outside air
temperature. Since the generated heat is radiated from the surface of the
cabinet, the temperature of the air in the cabinet and the outside air balance
at certain heat levels. If the amount of heat generated is constant, the
larger the surface area of the cabinet, the less the internal temperature
rises. The thermal design of the cabinet refers to calculating the heat
generated in the cabinet, evaluating the surface area of the cabinet, and
enlarging that surface area by installing heat exchangers in the cabinet, if
necessary. Such a design method is described in the following
subsections.
The cooling capacity of a cabinet made of sheet metal is generally 6 W/°C
per 1m
2
surface area, that is, when the 6W heat source is contained in a
cabinet having a surface area of 1 m
2
, the temperature of the air in the
cabinet rises by 1°C. In this case the surface area of the cabinet refers to
the area useful in cooling , that is, the area obtained by subtracting the area
of the cabinet touching the floor from the total surface area of the cabinet.
There are two preconditions : The air in the cabinet must be circuited by
the fun, and the temperature of the air in the cabinet must be almost
constant.
The temperature rise inside the cabinet is represented by the expression
below, with respect to the outside air temperature.
Internal heat loss P [W] x
6[W/m
2
⋅°C] × surface area S[m
2
]×10[°C] of rise in temperature
For example, a cabinet having a surface area of 4m
2
has a cooling capacity
of 24W/°C. To limit the internal temperature increase to 10°C under these
conditions, the internal heat must not exceed 240W. If the actual internal
heat is 320W, however, the temperature in the cabinet rises by 13°C or
more. If the allowable ambient temperature conditions for the units
cannot be satisfied, the cooling capacity of the cabinet must be improved
using the heat exchanger described below.
As discussed above, if the temperature rise cannot be limited to the
allowable level by the cooling capacity of the cabinet, a heat exchanger
must be added. The heat exchanger forcibly applies the air from both the
inside and outside of the cabinet to the cooling fin to obtain effective
cooling. The heat exchanger enlarges the surface area.
The customer should prepare the heat exchanger if necessary.
Name Heat loss
Power Mate 0 control unit 40W
CRT/MDI 18W
DPL/MDI 8W
CRT control PCB 4W
See FANUC SERVO MOTOR β series DESCRIPTIONS (B–65232EN)
for heat loss of servo amplifier.
3.4
THERMAL DESIGN
OF THE CABINET
3.4.1
Temperature Rise
within the Cabinet
3.4.2
Cooling by Heat
Exchanger
3.4.3
Heat Loss of Each Unit