250 Series Thin Stackohm® Vitreous Enamel Power Resistor Datasheet

Category: Electronics, Ohmite Manufacturing Co, Resistors

Overview

Ohmite’s 250 Series Thin Stackohm® Vitreous Enamel Power Resistors are designed for applications with space limitations, featuring a small size-to-power ratio and stackable design. These resistors are oval-shaped and constructed with a low profile to fit in tight spaces. An added benefit of the integral mounting brackets not only allows for secure attachment to surfaces but also enhances heat sinking capabilities, allowing for a more compact size per watt ratio.

Features

Stackable Design: Equipped with integral mounting brackets, facilitating fastening to a chassis.
Low Profile: Suitable for use in equipment where space is limited.
All-Welded Construction: Ensures durability and reliable performance.
Lead-Free Vitreous Enamel: The coating is compliant with RoHS standards, indicating reduced use of hazardous substances.

Series Specifications

The 250 Series is available in various wattage options ranging from 10 watts to 55 watts, with resistance values between 1.0 ohm and 50k ohms. The maximum voltage capacity of these resistors is determined by Ohm’s Law and limited by the resistance value of the specified product. For a RoHS compliant resistor, an “E” suffix should be added to the part number upon ordering.

Resistor Variants

F10 – 10 watts, 1.0-15K ohms, 187 volts max.
F20 – 20 watts, 1.0-50K ohms, 815 volts max.
F30 – 30 watts, 1.0-10K ohms, 281 volts max.
F40 – 40 watts, 1.0-25K ohms, 655 volts max.
F55 – 55 watts, 1.0-30K ohms, 1405 volts max.

Adjustable versions and other sizes are available upon consulting with Ohmite. There is also an option for lower-cost Centohm or Silicone coatings.

Characteristics

The resistors have a tinned lug with hole terminals, a linear derating from full power at +25°C to zero power at +350°C, and standard tolerances are ±5%. Power ratings are based on mounting the resistor on a metal surface and should be reduced by 15% when mounted on non-metallic surfaces. The resistors are designed to handle an overload of 10 times the rated wattage for 5 seconds without exceeding the maximum voltage, and they exhibit a positive temperature coefficient with different values for temperature ranges up to and over 200°C.

Dielectric Withstanding Voltage

10 and 20 watt ratings: 500 VAC
30, 40, and 55 watt ratings: 1000 VAC

These ratings are measured from the lug to the mounting bracket. To determine maximum current, the formula V=√(P*R) should be used.

Contact Information

For further inquiries or to order, customers can reach Ohmite by phone at 1-866-9-OHMITE, by fax at 1-847-574-7522, or by email at info@ohmite.com. More information is available on their website www.ohmite.com.