Specialized and Specific Application Resistors

Bleeder, meter multiplier, equalizing, and termination and load resistors.

Normal common resistors are┬ánot good for high voltage. Small resistors in the 1/2 to 2 watt range typically have safe wire-to-wire voltage ratings between 300 and 600 volts. The exact rating is given in manufacturer’s data sheets.

Carbon and normal metal resistors are also not RF rated. Since around 1980 almost all resistors switched to a LASER cut resistive coating that spirals around a ceramic core. To handle high surges and have low RF inductance, a resistor has to be a composition type. The superior composition type is now a metal composition.

Carbon composition is long term problem at elevated temperatures. While conductor based resistors like metal film or wire wound generally only increase in resistance or open over time or with abuse, carbon resistors can significantly decrease in resistance from heat or abuse.

18K ohm resistor aged down from heat

18K carbon failed short

Carbon or standard wire-wound resistors also develop lead connection issues with moisture. This can cause resistors stored in humid locations to age “open” or upward in value.

Stackpole is one of the last manufacturers of true carbon compositions suitable for RF applications. We carry carbon compositions. Standard carbon films can look exactly like a composition. The only way to tell a rare carbon composition from a more inductive carbon film is by manufacturer’s part number or by cutting a sample resistor open.

Resistors can look alike and share a name n=but be d far different in function

Resistor Styles Inside and Outside

 

All carbon resistors in high temperature, high voltage, humid, or high surge applications are now better replaced with superior metal composition or thick film resistors. Metal compositions handle repeated exposure to gross surges and overloads (including lightning), humidity and moisture, and physical abuse much better than any carbon. They are also more suitable for parasitic suppressors.

Above all, make sure the voltage rating of any resistor is higher than the applied voltage!

We carry special surge or fault limiting resistors rated at up to 11kV from lead-to-lead!

We carry all types of specialized hard-to-find resistors and superior performance for voltage equalizing, parasitic suppressor, and meter multiplier applications. We know the important differences that fit resistors to specific applications.