Custom Case Study
The customer’s design engineers faced several constraints when placing a temperature sensing solution in their integrated junction power box. This design required two sensors placed in two different system locations. Functionally, the sensors would control a circuit that reduces current when an abnormal or fast temperature rise is detected.
The temperature sensor assemblies were intended to be mounted on busbars using lugs. However, the sharp edges of aluminum busbars can sometimes damage the wire insulation material of thermistor assemblies. This was especially problematic considering that the wire positions wouldn’t be fixed, as these systems often experience high mechanical shock and vibration forces during operation. Also, the busbars might be subjected to very high temperatures, which meant that standard plastic wire insulation alone wasn’t viable, as it could melt and cause a short.
As they would be employing two sensors of the same style in two different locations in the system — but with different R25 values and cable lengths — it was important to be able to distinguish between the two assemblies for selection and placement during manufacturing. The final solution also had to be compliant with AEC-Q200, offer a high isolation voltage of 2.7 kVAC up to +150 °C, and feature an M4 mounting screw size.
Vishay’s design engineers created an assembly based on the NTCALUG91A standard lug sensors, which feature an M4 screw mounting.
The final end product features two sensors with different cable lengths and wire colors mounted on the same connector. To protect the connection cables from the sharp edges on the busbars, they are in glass fiber insulation tubes. This wire casing masked the wire insulation colors and prevented visual inspection, which meant that another solution for differentiating the two sensors was necessary. It was decided to add a colored dot on the neck of the lug for one of the two sensors, which can be easily detected via automated visual inspection.
Custom assembly with two temperature sensors
This cost-effective solution offers our customer precise and secure temperature control of their integrated power box, prevents damage to the sensors and connecting cables, allows for variable design positions, and improves the reliability of the final application.
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