Bourns Adds to its Model CSM2F High Power Current Sense Resistor SeriesMarch 12, 2021 by Gary Elinoff
The enhanced line of current sense resistors are aimed at battery management systems and industrial control.
The nine new members of the CSM2F Series feature resistances ranging from 25 to 200 micro ohms.
All members of the Model CSM2F series offer resistance values from as low as 25 microohms up to 200 microohms. The units can handle continuous power dissipations of up to 50 watts and continuous currents of up to 1414 amps. Series members also feature high pulse power handling capabilities.
Members of Bourns’ CSM2F Series of Current Sense Resistor. Image courtesy of Bourns
What are Current Sense Resistors?
The voltage across the current sense resistor is measured. Because, as per Ohm’s Law, Current is equal to that Voltage divided by the Resistance, the current flowing through the resistor is easily calculated by measuring the voltage across the resistor.
However, some power, inevitably, is wasted in the resistor. That power is equal to I2R. And, wherever there is wasted power, there is also unwanted, parasitic heat generated. Thus, the resistor’s value must be chosen to be as low as practicable.
Despite this somewhat minor drawback, Bournes reports that current sense resistors are “growing in popularity due to their high measurement accuracy and relatively low cost compared to other technologies.”
Two New Terminal Surface Treatments
These two new methods of surface finishing are described as fully-plated and bare copper.
After metal stamping these resistors are subjected to a tin-plating process to build a protective layer. This provides for lower resistance drift, enhanced performance and for long-term stability.
In pursuit of enhanced TCR performance, this version is constructed without tin-plating. To help extend resistor lifespan, the copper terminals are covered with a protective layer.
The series is manufactured using an electron beam (E-Beam) welded resistive copper alloy. The metal alloy current sensing element of the resistor provides a temperature coefficient of resistance (TCR) of only 50 PPM/°C in the 20 °C to 60 °C temperature range. Additionally, that same metal alloy current sensing element also engenders a thermal EMF as low as 0.25 µV/K
All members of the Model CSM2F series, both new and old, are available in one of four package sizes; they are designated the 6918, 8518, 7036. The 8536 is designated a “metric” size. Of the 12 members, three are available in each of the four package types.
Bourns supplies a link to all its AEC-Q200 compliant resistors, including the CSM2F series. There are 12 members of the CSM2F listed, but no readily apparent way to know which ones are are part of the nine member “new” group. The interested reader will be pleased to note that links to all 12 members are available with one left click on the AEC-Q200 compliant resistor page.
Members of the CSM2F series will find application in high current applications such as battery management system (BMS) and industrial control and other high current applications.
Package sizes, as the reader will note, are spelled out in the package’s name:
- 8518: 85 x 18 mm
- 8536: 85 x 36 mm
- 6918: 69 x 18 mm
- 7036: 70 x 36 mm
- AEC-Q200 compliant
- The new current sense resistors are RoHS compliant