WFH Series
L
ø4.5
Aluminum Housed Wirewound Power
12.6
6.3
0.8
13.6
8
41
51
Amp
terminal
15
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 sensi-
tive 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
mounting surface.
SPECIFICATIONS
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 temperature 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.
FEATURES
• Solder, wire and “Fast-On”
Termination
• More resistors in one profile pos-
sible
• Custom wire lengths available
B
A
10
300
ø2.2
4.8
POWER DISSIPATION
350
300
W/Resistor
0.6
6
250
200
150
100
WFH330
WFH230
WFH160
WFH90
Lug
terminal
Power
Rating*
(watts)
90
160
230
330
Resistance
Range
(Ω)
0.22Ω – 6.8K
0.47Ω-18K
0.82Ω-27K
1Ω - 39K
Wire
terminal
50
0
Type
WFH90
WFH160
WFH230
WFH330
Dimension (mm)
A
B
L
70
39.7
53
140
80
123
210
2x 80 193
280 2x 100 263
80°
100°
120°
140°
Heat Sink Temperature,
°C
This graph shows the maximum wattage rating for each possible resistor
of standard size corresponding to the heat sink temperature. It is as-
sumed that all resistors are equally loaded.
40°
60°
THERMAL RESISTANCES
Thermal Resistance (°C/W) between different
measuring points
R
TH
1
R
TH
2
R
TH
3
R
TH
4
WFH90 WFH160 WFH230 WFH330
2
1
0.75
0.5
6.8
3.9
2.75
2
0.1
0.05
0.03
0.02
0.3
0.17
0.1
0.085
resistor
surface to
heat sink
*at 40°C base plate temperature
R
TH4
aluminum
housing
to air
R
TH2
DESIGNING
The following equations are applied in the dimensioning of the resistors at
stationary load. If more information is required please consult Ohmite. It is
assumed that the air around the resistors is stationary (worst case).
See
ohmite.com for more examples.
1. WFH is mounted on a heat sink:
A. The thermal resistance R
TH
of the heat sink is known,
T = W
MAX
x (R
TH4
+ R
TH
)
Check that:
T
MAX
= W
MAX
x (R
TH
+ R
TH3
+ R
TH1
) + T
AMB
<220°C
B. The Temperature of the Heat Sink is known,
T = W
MAX
x R
TH4
+ T
H
Check that:
T
MAX
= W
MAX
x (R
TH1
+ R
TH3
) + T
H
<220°C
2. WFH is mounted without a heat sink:
Check that:
T
MAX
= W
MAX
x (R
TH1
+ R
TH2
) + T
AMB
<220°C
Where:
W
MAX
= Maximum reguired load in resistor
T
MAX
= Maximum hot spot temperature reguested in resistor (T
MAX
<220°C) The lower T
MAX
the higher reliability and lifetime.
T
AMB
= Ambient temperature
R
TH
= Thermal resistance. Refer to table Thermal resistances
T
H
= Heat sink temperature (chassis).
T
= Temperature on top of the Aluminum profile.
30
aluminum
housing to
heat sink
R
TH3
R
TH1
wire to
aluminum
housing
O R D E R I N G I N F O R M AT I O N
�½�½�½�½�½�½�½�½�½�½�½�½
Series
Wattage
at 40°C
base plate
temp.
RoHS
Compliant
Tolerance
Ohms
Terminal Type
J = 5%
L = lug terminals R47= 0.47Ω K = 10%
A = amp terminals
W= 30cm insulated wire cable 18AWG
Check product availability at
www.ohmite.com
S TA N D A R D PA RT N U M B E R S F O R W F H S E R I E S
WFH90L4R7KE
WFH90L10RKE
WFH90L25RJE
WFH90L50RJE
WFH90L100JE
WFH90L470JE
WFH90L750JE
WFH90L1K0JE
WFH90L2K7JE
WFH90L5K0JE
WFH160LR47KE
WFH160L1R0KE
WFH160L2R0KE
WFH160L10RKE
WFH160L27RJE
WFH160L50RJE
WFH160L75RJE
WFH160L100JE
WFH160L150JE
WFH160L250JE
WFH160L1K0JE
WFH160L5K0JE
WFH160L10KJE
WFH230L1R0KE
WFH230L2R0KE
WFH230L5R0KE
WFH230L10RKE
WFH230L27RJE
WFH230L50RJE
WFH230L75RJE
WFH230L100JE
WFH230L150JE
WFH230L250JE
WFH230L1K0JE
WFH230L1K5JE
WFH230L2K5JE
WFH330L1R0KE
WFH330L2R0KE
WFH330L10RKE
WFH330L27RJE
WFH330L50RJE
WFH330L75RJE
WFH330L100JE
WFH330L150JE
WFH330L250JE
WFH330L1K0JE
WFH330L5K0JE
WFH330L10KJE
Ohmite Mfg. Co.
1600 Golf Rd., Rolling Meadows, IL 60008 • 1-866-9-OHMITE • Int’l 1-847-258-0300 • Fax 1-847-574-7522 • www.ohmite.com • info@ohmite.com
OHMITE [ OHMITE MFG. CO. ]
