Overview of Ohmite 270 Series Fixed Resistors
The Ohmite 270 Series Fixed Resistors are designed for high wattage applications, offering a range of resistors suitable for soldering or bolt connection and are compliant with RoHS standards. These resistors are particularly constructed for demanding situations where high reliability is a must.
Material and Construction
The resistors are coated with lead-free vitreous enamel, with options for either low-cost Centohm or Silicone Ceramic coatings, and are composed of a tubular ceramic core. The series boasts an all-welded construction, enhancing their durability for high-performance use.
Specifications and Ratings
The 270 Series encompasses a wide range of resistance values, from 0.1 ohms to over 250 kilohms, with wattage ratings from 12W to 1000W. The power rating is based on a stable ambient temperature (25°C free air rating). Models above 750 watts come in very large sizes, equipped with lug terminals conducive for robust connections. Resistors come with a standard tolerance of ±10% for values under 1 ohm and ±5% for larger values.
Features and Options
One of the standout features of the 270 Series resistors is their high power handling, showcasing a linear derating from 100% capacity at +25°C to 0% at +350°C. These resistors are capable of enduring an overload of 10 times the rated wattage for 5 seconds.
Non-inductive versions are available upon request. Additional features like “FFast on” terminals offer versatility in mounting options, and models can accommodate spring-type brackets, thru-bolts, or slotted-steel brackets for secure mounting.
Dielectric Withstanding Voltage and Temperature Coefficient
The dielectric withstanding voltage ranges from 1000 VAC for resistors with a 12 to 100 watt rating to 3000 VAC for wattage ratings between 175 to 225 watts. The temperature coefficient varies depending on the resistance value, from +400 ppm/°C for resistances from 1 to 20 ohms and +260 ppm/°C for values above 20 ohms.
Ordering Information and Standard Part Numbers
To order, options are provided to customize the core diameter, coating, and terminal types according to the specified requirements, along with a list of standard part numbers for ease of selection. The datasheet also lists a selection of standard part numbers for the series, which are available for inventory search on the Ohmite website.
Contact Information
For further technical assistance, custom orders, or to consult the factory for mounting options referenced on page 36 and 37 of the Ohmite datasheet, contact details are provided for Ohmite Manufacturing Company, including toll-free and international phone numbers, fax, and email.
The 270 Series Fixed Resistors are made-to-order parts and can be configured for power, resistance value, tolerance, and coating type based on the needs of high wattage applications.
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