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WFH Series
Aluminum Housed Wirewound Power
Power rating
90W-330W
Resistance
tolerance
±5%, ±10%
Temperature
Coefficients
Normal: 50ppm - 150ppm
Low ohmic values: 400ppm
Dielectric
strength
2500 VAC peak
Working voltage
1200 VAC
Test voltage
6000 VAC
Lead wire
(wire terminal version only): XLPE, 600V, 125C,
18 AWG stranded
Insulation
Silicone Rubber & Mica. The Silicone is
UL-recognised (UL 94 HB) to a working tem-
perature of 220°C. Temperatures of up to
300°C can be endured for shorter periods.
This may however cause an expansion of the
silicone rubber with a possibility of reducing
the dielectric strength.
Min. Storage &
Operating Temp.
-40˚C
Power Rating* Resistance Range
Type (watts) (Ω)
WFH90 90 0.22Ω – 6.8K
WFH160 160 0.47Ω-18K
WFH230 230 0.82Ω-27K
WFH330 330 1Ω - 39K
*at 40°C base plate temperature
W/Resistor
Heat Sink Te mperature, °C
40° 60° 80° 100° 120° 140°
100
150
200
300
50
250
350
0
WFH330
WFH160
WFH230
WFH90
Power Dissipation
Ohmite’s new flat core winding technology allows for wire-
wound heatsinkable resistors affording a very low profile, and
superior thermal transfer characteristics when compared to
conventional aluminum housed wirewound resistors.
Close mounting of heat sensitive components is possible
due to only a slight rise of the temperature on the aluminum
profile.
No heat sink compound is required because of large mount-
ing surface.
This graph shows the maxi-
mum wattage rating for each
possible resistor of standard
size corresponding to the
heat sink temperature. It is
assumed that all resistors
are equally loaded.
resistor
surface to
heat sink
R
TH
4
R
TH
1
wire to
aluminum
housing
aluminum
housing
to air
R
TH
2
R
TH
3
aluminum
housing to
heat sink
Thermal Resistances
Thermal Resistance (°C/W) between different
measuring points
WFH90 WFH160 WFH230 WFH330
R
TH
1
2 1 0.75 0.5
R
TH
2
6.8 3.9 2.75 2
R
TH
3
0.1 0.05 0.03 0.02
R
TH
4
0.3 0.17 0.1 0.085
THIS PRODUCT IS DESIGNED FOR
USE WITH PROPER HEATSINKING.
Maximum base plate temperature of the resistor must be monitored
and kept within specified limits to establish the power rating. Best
technique is to attach a thermocouple to the side of the base plate of
the resistor. Temperature of plastic housing or heat sink cannot be
used to establish rating of the resistor.
FEATURES
•Solderlug,wire,and“Fast-on”ampter-
minations
•Multipleresistorsinoneprofilepossible
•Customwirelengthsavailable
CHARACTERISTICS
SERIES SPECIFICATIONS
(continued)
