WFH Series Aluminum Housed Wirewound Power 12.6 L 6.3 ø4.5 0.8 8 13.6 Amp terminal 41 51 15 B A 10 300 WFH330 250 200 WFH230 150 WFH160 100 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 Dimension (mm) A B L 70 39.7 53 140 80 123 210 2x 80 193 280 2x 100 263 *at 40°C base plate temperature 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 RTH of the heat sink is known, T = WMAX x (RTH4 + RTH) Check that: TMAX = WMAX x (RTH + RTH3 + RTH1) + TAMB <220°C B. The Temperature of the Heat Sink is known, T = WMAX x RTH4 + TH Check that: TMAX = WMAX x (RTH1 + RTH3) + TH <220°C 2. WFH is mounted without a heat sink: Check that: TMAX = WMAX x (RTH1 + RTH2 ) + TAMB <220°C Where: WMAX = Maximum reguired load in resistor TMAX = Maximum hot spot temperature reguested in resistor (TMAX <220°C) The lower TMAX the higher reliability and lifetime. TAMB = Ambient temperature RTH = Thermal resistance. Refer to table Thermal resistances TH = Heat sink temperature (chassis). T = Temperature on top of the Aluminum profile. 30 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 ULrecognised (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. 350 0.6 6 Type WFH90 WFH160 WFH230 WFH330 SPECIFICATIONS POWER DISSIPATION W/Resistor 4.8 FEATURES • Solder, wire and “Fast-On” Termination • More resistors in one profile possible • Custom wire lengths available 300 ø2.2 Ohmite’s new flat core winding technology allows for wirewound 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 mounting surface. WFH90 50 0 40° 60° 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 assumed that all resistors are equally loaded. THERMAL RESISTANCES resistor surface to heat sink Thermal Resistance (°C/W) between different measuring points RTH1 RTH2 RTH3 RTH4 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 aluminum housing to air RTH4 RTH3 aluminum housing to heat sink RTH2 RTH1 wire to aluminum housing O R D E R I N G I N F O R M AT I O N ������������ 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 • [email protected]