1-866-9-OHMITE • Int’l 1-847-258-0300 • Fax 1-847-574-7522 • www.ohmite.com • info@ohmite.com

133

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

Heat Sink Temperature, °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

wire to

aluminum

housing

aluminum

housing

to air

aluminum

housing to

heat sink

Thermal Resistances

Thermal Resistance (°C/W) between different

measuring points

WFH90 WFH160 WFH230 WFH330

1

0.75

0.5

3.9

2.75

2

0.05

0.03

0.02

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.

Fea ture S

•Solderlug,wire,and“Fast-on”ampter-

minations

•Multipleresistorsinoneprofilepossible

•Customwirelengthsavailable

c H aracteri S tic S

S erie S SP eci F icati ONS

(continued)