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Stackpole Product Highlight - High Power Chassis Mount Or Heat Sink Mount Resistors


High Power Chassis Mount Or Heat Sink Mount Resistors

This product highlight will discuss Stackpole's non-surface mount high power resistors. Because these resistors utilize external methods to remove heat, they are specified and used differently than many other axial leaded power resistors. It is important to understand the unique ratings and requirements for these resistors to ensure proper sizing, performance, and long term reliability.

Chassis Mount Resistors

Chassis mount resistors are unique in that they are not typically mounted on a circuit board. Instead they are mounted to a metal cabinet, enclosure, or motor housing. They rely on this metal mounting surface to help dissipate the heat they generate. Unlike most resistors, they are rated for full power up to 25°C instead of 70°C or higher. It is important that the engineer understand this power rating limitation and the need to keep the resistive element within its normal operating temperature range.



KAL Series Aluminum Housed Wirewounds

The KAL series utilizes a welded wirewound element that is epoxy molded into an aluminum housing. The housings have tabs on their base for screw mounting or riveting them to the enclosure where they are used. The bottom of the housing is extremely smooth and flat which lends itself to using a thermally conductive grease or paste between the housing and the enclosure to enhance the conduction of heat away from the part. This is necessary because the part is rated for full power up to 25°C and must be derated for any ambient temperatures above that. However, these parts can operate up to 275°C so they can be used under extreme temperatures and harsh environments.

The KAL is available in power ratings from 12.5 watts up to 250W, in tolerances as tight as 0.1%, and values ranging from 0.05 ohm to 150K ohms. The KAL has standard rigid metal tab terminals for connection with most types of wiring. The KAW is a variation that provides standard 6" insulated wire leads with 1/2 inch strip at the ends. Stackpole also has the capability to provide a wide variety of connectors on the ends of those wire leads as well as different wire lengths to support a wide range of customer requirements. The KAL's can be provided with non-inductively wound elements which greatly reduces the inductance of the device. Pricing for the KAL varies with size, tolerance and resistance value and ranges from $1.00 each to $16.25 each in minimum quantities. Non-inductive windings, stranded wire leads, crimped connectors, or other special requirements may add cost (contact factory for details).



SWT / EWT Tubular Wirewound Resistors

The SWT / EWT are tubular wirewounds with open cores and large rigid metal tab terminations. They are typically mounted to a motor housing or enclosure either using the customer's preferred mounting hardware or from hardware provided with the part by adding an M to the end of the part numbers, SWTM and EWTM. Their power rating is based on a 25°C full power temperature and derates to zero power at 350°C. As with the KAL Series, even though their full power rating is limited and requires external heat removal for ideal operation, the part can operate safely in extremely high temperatures.

The SWT and EWT are available in sizes from 12 watts up to 300 watts. The SWT contains a silicone coating and the EWT contains a vitreous enamel coating that is impervious to moisture and withstands extremely high temperatures of up to 500°C. Resistance values range from 0.1 ohm up to 240K ohms in tolerances of 5% to 10%. A variety of options are available in this series including non-inductively wound, adjustable center tap, spring clip mounting for smaller sizes, and welded straight wire leads. Pricing varies with size, resistance value, tolerance, and coating choice, and ranges from $1.00 each up to $29 each in minimum quantities.


Applications for these large size chassis mount resistors include a wide array of motor protection and control, dynamic braking, capacitor bank discharge, welding equipment, and plasma cutters.



TR Series TO-220 and TO-247 Type Power Resistors

The TR series is a thick film technology on a ceramic substrate that is then bonded to flat metal plate. This metal plate is then attached to a heat sink. The part is commonly used with power semiconductors that also utilize a heat sink for power dissipation. By increasing the capacity of the heat sink, the engineer is able to use a resistor with a very high power to size ratio. Like the chassis mount parts previously discussed, the power rating is full power to 25°C, which is standard for resistors that utilize external cooling. However since the resistance element is thick film, they are derated to zero power at 150°C for the TR20, 30, 50, and 50H and to zero power at 175°C for the TR35 and 100.

The TR series is available in power ratings of 20 watts through 100 watts assuming 25°C case temperature and heat sink attachment. Resistance values range from 0.05 ohm to 100K ohms in tolerances of 0.5%, 1%, 5%, and 10%. TCR is dependent on resistance value and ranges from 50 ppm to 300 ppm. The TO-220 size of the 20W through 50W sizes is approximately 10mm by 16mm. The TO-247 size 100W is around 16mm by 21mm. The 30, 35, 50H, and 100 watt sizes have a screw hole to help secure the part to the heat sink. The 20 and 50 watt sizes utilize a spring clip mount. Pricing varies with power rating, resistance value, tolerance, and TCR, and ranges from $1.75 each to $5.38 each in full package quantities.



More Information and Data Sheets:

For more information about Stackpole products, contact Stackpole Electronics, Inc. at

Stackpole Electronics, Inc.
2700 Wycliff Road Suite 410,
Raleigh NC 27607
phone: 919-850-9500

Stackpole Electronics Inc. is a leading global manufacturer of resistors supplying to the worlds largest OEMs, contract manufacturers and distributors. Headquartered in Raleigh, N.C., the privately held company began manufacturing in 1928 as part of Stackpole Carbon Company in St. Mary's, Pennsylvania. Now part of the Akahane Stackpole Manufacturing Group (ASMG), Stackpole has manufacturing facilities in Japan, Taiwan, China and Mexico; warehousing facilities in El Paso, Shenzhen and Japan; and international sales offices in Tokyo, Taipei, London, Hong Kong and Shenzhen.


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