The sigma resistors cover a power range from 100W to 7kW average load and it is a popular economically type of brake resistors. The resistor components consist of fully welded wire wound ceramic resistors, which is a well-known and proven technology. The base material is cordierite, which is a type of ceramic with a very high resistance to temperature changes and the wire is coated with aluminum phosphate which protects the wire and conducts the heat developed in the wire onto the ceramic core. Aluminum-phosphate is stable up to 500°C. The resistor cages comply with IP20 (IP21 for UL versions) giving electrical and thermal protection. These resistors having a nominal load from 100W - 7kW and are particularly suitable for pulse load of 10 - 20 times higher compared to the nominal load because of the ceramic core material and an extra high weight of the wire.
We offer THERMAL MODELS corresponding to all resistor types and resistor values. By using these models we are able to calculate the temperature rise in the resistor wire for all possible load situations. With this simulations we can find the optimal solution for your application.