Specifications are subject to change without notice (28.04.2015) 5
Applications
Thermal characteristics
The thermal design of Solid
State Relays is very impor-
tant. It is essential that the user
makes sure that cooling is ad-
equate and that the maximum
junction temperature of the re-
lay is not exceeded.
This relay is designed for use
in applications in which it is
exposed to high surge condi-
tions. Care must be taken to
ensure proper heatsinking
when the relay is to be used at
high sustained currents. Ade-
quate electrical connection
between relay terminals and
cable must be ensured.
RA 24.. .. 06, RA 44.. .. 08, RA 48.. .. 12
Heat flow
Heatsink
temperature
R
th
j-c
R
th
c-s
R
th
s-a
Junction
temperature
Case
temperature
Ambient
temperature
Thermal resistance:
R
th
j-c = junction to case
Direct bonding
In the design of the output
power semiconductor direct
bonding of the copper layer
and the ceramic substrate has
been applied. This is to en-
sure uninhibited heat transfer
and high thermal fatigue
strength.
The relay has been designed
for applications requiring lar-
ge numbers of load cycles.
Power dissipation
The power dissipation for in-
termittent use is calculated ac-
cording to the following for-
mula:
t
on
t
off
OFF
ON
I
rms
=
I
ON
2
x t
ON
t
ON
+ t
OFF
Ex: RA 24 50 -D 06:
Load current = 45 A
t
ON
= 30 s
t
OFF
= 15 s
I
rms
=
45
2
x 30
30 + 15
The rms current will be
36.7 A.
If the heatsink is placed in a
small closed room, control
panel or the like, the power
dissipation can cause the
ambient temperature to rise.
The heatsink is to be cal-
culated on the basis of the
ambient temperature and the
increase in temperature.
R
th
c-s = case to heatsink
R
th
s-a = heatsink to ambient
• Heatsinks and fans
• 5.40
o
C/W to 0.12
o
C/W thermal resistance
• DIN, panel or thru wall mounting
• Single or multiple SSR mounting
Heatsink Selection
Heatsink Range Overview:
http://www.productselection.net/PDF/UK/ssr_accessories.pdf
Heatsink Selector Tool:
http://www.productselection.net/heatsink/heatsinkselector.php?LANG=UK
Ordering Key
RHS..
