RPS 250
Vishay Sfernice
Document Number: 50007 For technical questions, contact: sfer@vishay.com www.vishay.com
Revision: 24-Nov-08 31
Power Resistor for Mounting onto a Heatsink
Thick Film Technology
FEATURES
•High power rating: 250 W
•High overload capability up to 4 times nominal
power (see energy curve)
•Easy mounting
•Low thermal radiation of the case
Developed for specific applications such as railroad electrical traction, this series can bear short overloads as high as fifteen times
the nominal power. Designed to be mounted onto a heatsink, these power resistors exhibit remarkable characteristics.
DIMENSIONS in millimeters
MECHANICAL SPECIFICATIONS
Mechanical Protection Insulated case
Substrate Alumina onto
aluminum base
Resistive Element Cermet
End Connections Screws M4, (M5 on
request)
Tightening Torque on connections 2 Nm
Weight 170 g ± 10 %
ENVIRONMENTAL SPECIFICATIONS
Thermal Resistance RTH (j-c) 0.22 °C/W
Temperature Range - 55 °C + 125 °C
Climatic Category 55/125/56
• Tolerance unless stated: ± 0.2 mm
73
56
7
. 5
57
34
Ø 7.2
Ø 4.2
8 . 5 3
2 M4 USEFUL DEPTH: 8
RPS 250D
5
.
0
1
0 6
1 2 Ø
26 ± 1
16.5
ELECTRICAL SPECIFICATIONS
Resistance Range
0.24
Ω
to 1M E24 series
Tolerances
± 1 % to ± 10 %
Power Rating chassis mounted
250 W
1000 W
at 50 °C continuous
at 25 °C for 10 s
Temperature Coefficient
Standard
± 250 ppm/°C < 1
± 150 ppm/°C > 1
Limiting Element Voltage U
L
5 kVRMS
Dielectric Strength
MIL STD 202 (301), 1 min, 10 mA max.
L connections 7 kVRMS
H connections 12 kVRMS
Insulation Resistance
> 10
6
M
Ω
Inductance
< 50 nH
Capacitance Resistor/
ground
< 40 pF
< 120 pF
www.vishay.com For technical questions, contact: sfer@vishay.com Document Number: 50007
32 Revision: 24-Nov-08
RPS 250
Vishay Sfernice Power Resistors for Mounting onto a Heatsink
Thick Film Technology
CHOICE OF THE HEATSINK
The user must choose the heatsink according to the working conditions of the component (power, room temperature).
Maximum working temperature must not exceed 125 °C. The dissipated power is simply calculated by the following ratio:
P: Expressed in W
T: Difference between maximum working temperature and room temperature
RTH: (j-c): Thermal resistance value measured between resistive layer and outer side of the resistor. It is the thermal
resistance of the component: (see specifications environmental paragraph).
RTH: (c-a): Thermal resistance value measured between outer side of the resistor and room temperature. It is the thermal
resistance of the heatsink, depending on the heatsink itself (type, shape) and the quality of the fastening device.
Example:
RTH: (c-a) for RPS 250 power dissipation 180 W at + 50 °C room temperature.
ΔT ≤ 125 °C - 50 °C ≤ 75 °C
RTH (j-c) + RTH (c-a) = = = 0.42 °C/W
RTH (j-c) = 0.22 °C/W
RTH (c-a) ≤ 0.42 °C/W - 0.22 °C/W ≤ 0.20 °C/W
RECOMMENDATIONS FOR MOUNTING ONTO A HEATSINK
Surfaces in contact must be carefully cleaned. The heatsink must have an acceptable flatness: from 0.05 mm to 0.1 mm/100 mm.
Roughness of the heatsink must be around 6.3 µm. In order to improve thermal conductivity, surfaces in contact should be coated
with a silicone grease (type SI 340 from Rhône-Poulenc or Dow 340 from Dow Corning).
The fastening of the resistor to the heatsink is under pressure control of two screws (tightening torque 3 Nm).
In order to improve the dissipation, either forced-air cooling or liquid cooling may be used.
Do not forget to respect an insulation value between two resistors (dielectric strength in dry air 1 kV/mm).
In any case the hot spot temperature, measured locally on the case must not exceed 125 °C.
Test should be performed by the user.
PERFORMANCE
TESTS CONDITIONS REQUIREMENTS
Momentary Overload NF EN 140 000 CEI 115_1
4 Pr/10 s/UL = 5000 V < ± (0.25 % + 0.05 Ω)
Rapid Temperature Change
NF EN 140 000 CEI 68214 Test Na
5 cycles
- 55 °C + 125 °C
< ± (0.25 % + 0.05 Ω)
Load Life NF EN 140 000 CEI 115_1
1000 h Pr at 70 °C < ± (0.5 % + 0.05 Ω)
Humidity (steady state) MIL STD 202 Method 103 B and D
56 days R.H. 95 % < ± (0.5 % + 0.05 Ω)
RESISTANCE VALUE IN RELATION TO TOLERANCE AND TCR
Ohmic Value < 1 Ω> 1 Ω
Standard Tolerance ± 5 % ± 5 %
Standard TCR (- 55 °C to + 125 °C) ± 250 ppm/°C ± 150 ppm/°C
Tolerance On Request ± 1 % - ± 2 % - ± 10 %
PΔT
RTH jc–()RTH ca–()+[]
---------------------------------------------------------------------1()
=
ΔT
P
------- 75
180
----------
RPS 250
Power Resistor for Mounting onto a Heatsink
Thick Film Technology Vishay Sfernice
Document Number: 50007 For technical questions, contact: sfer@vishay.com www.vishay.com
Revision: 24-Nov-08 33
OVERLOADS
In any case the applied voltage must be lower than 2.5 Un. U maxi < 2.5 Un < 12 500 V.
Short time overload: 4 Pn/10 s
Accidental overload: The values indicated on the graph below are applicable to resistors in air or mounted onto a heatsink.
ENERGY CURVE
POWER RATING CHART
The temperature of the heatsink should be maintained in the limit specified.
To improve the thermal conductivity, surfaces in contact should be coated with a silicone grease.
MARKING
Series, style, ohmic value (in Ω), tolerance in %, manufacturing date, VISHAY trademark
PACKAGING
Packaging box of 15 units
ENERGY IN JOULES
OVERLOAD DURATION IN SECONDS
1 µs
0.13
1
10
100
1000
10 000
10 µs 100 µs 1 ms 1 s10 ms 100 ms
% RATED POWER
0 20 40 60 80 100 120 140
HEATSINK TEMPERATURE IN DEGREES CELSIUS
0
20
40
60
80
100
www.vishay.com For technical questions, contact: sfer@vishay.com Document Number: 50007
34 Revision: 24-Nov-08
RPS 250
Vishay Sfernice Power Resistors for Mounting onto a Heatsink
Thick Film Technology
GLOBAL PART NUMBER INFORMATION
GLOBAL
MODEL STYLE DIELECTRIC OHMIC VALUE TOLERANCE PACKAGING TYPE
RPS250 D = Diagonal
connections
A = Straight
connections
H = Dielectric
strength 12 kV
L = Dielectric
strength 7 kV
The first three digits
are significant figures
and the last digit
specifies the number
of zeros to follow.
R designates decimal
point.
2R20 = 2.20 Ω
48R7 = 48.7 Ω
47R0 = 47 Ω
1001 = 1 kΩ
4R70 = 4.7 Ω
R240 = 0.24 Ω
F = 1 %
G = 2 %
J = 5 %
K = 10 %
B = Box, 15 pcs
N = Box, 15 pcs
N/A
(1 to 14 pcs by box)
Standard RPS250A
= Blank
Standard
RPS250D = ZA3
Special = Blank
(for RPS250D) or as
applicable = ZAx
0250DL2 2 J ZP SR R0B 3A
Document Number: 91000 www.vishay.com
Revision: 18-Jul-08 1
Disclaimer
Legal Disclaimer Notice
Vishay
All product specifications and data are subject to change without notice.
Vishay Intertechnology, Inc., its affiliates, agents, and employees, and all persons acting on its or their behalf
(collectively, “Vishay”), disclaim any and all liability for any errors, inaccuracies or incompleteness contained herein
or in any other disclosure relating to any product.
Vishay disclaims any and all liability arising out of the use or application of any product described herein or of any
information provided herein to the maximum extent permitted by law. The product specifications do not expand or
otherwise modify Vishay’s terms and conditions of purchase, including but not limited to the warranty expressed
therein, which apply to these products.
No license, express or implied, by estoppel or otherwise, to any intellectual property rights is granted by this
document or by any conduct of Vishay.
The products shown herein are not designed for use in medical, life-saving, or life-sustaining applications unless
otherwise expressly indicated. Customers using or selling Vishay products not expressly indicated for use in such
applications do so entirely at their own risk and agree to fully indemnify Vishay for any damages arising or resulting
from such use or sale. Please contact authorized Vishay personnel to obtain written terms and conditions regarding
products designed for such applications.
Product names and markings noted herein may be trademarks of their respective owners.
