Ohmite EBW Current Sensing

Thermal shock (-65 ℃) ↔ 125 ℃, 25 cycles): ± 0.1%

Short term overload (5 times rated power, 5 seconds): ± 0.2%

Welding heat resistance (350 ℃ for 30 seconds or 250 ℃ for 10 minutes): ± 0.2%

Moisture resistance (10 cycles, high humidity, high low temperature): ± 0.2%

High temperature exposure (140 ℃, 250 hours): ± 0.2%

High frequency vibration (15g, 10-2000 Hz, 36 times): ± 0.2%

Load life (2000 hours, 90 minutes ON/30 minutes OFF): ± 1.0%

These data indicate that the EBW series has extremely high reliability in harsh environments such as automotive electronics and industrial control.

Selection guide: Manganin vs NiCr

3.1 Application scenario analysis

Reasons for recommending alloys based on application requirements

Battery Management System (BMS), with a current accuracy requirement of ± 1% Manganin and low TCR, with minimal drift across the entire temperature range

Motor driver, current detection is used for overcurrent protection NiCr or Manganin. If the ambient temperature changes greatly, Manganin is selected; If cost sensitive and software compensated, choose NiCr

Inverter output current feedback (high frequency) Manganin low inductance (both<3 nH), but Manganin lower thermal EMF

Welding machine/pulse power equipment Manganin low resistance high pulse energy absorption capacity

Automotive 12 V/48 V system, continuous 150 A+EBWB-M 0.2 m Ω extremely low loss, temperature rise controllable

3.2 Principle of Resistance Selection

Maximum Voltage Drop: Typically designed for full range of 50-100 mV to reduce losses. For example, using 0.5 m Ω for a current of 100 A generates a 50 mV voltage drop.

Power consumption: P=I ² R must be less than the rated power (considering derating). If the ambient temperature is 85 ℃, the EBWA power needs to be reduced to about 2.5 W (estimated linearly).

Thermal coupling: In high-density layouts, sufficient spacing should be left between multiple resistors to avoid thermal concentration.

3.3 Typical faults: premature drift or burnout

Phenomenon: Within the nominal current, the resistance value exceeds the tolerance or is open circuited.

troubleshoot

Check if it exceeds the pulse energy curve. Even if the average power does not exceed, transient surges (such as capacitor charging) may damage the resistance.

Measure the surface temperature of the resistor. If the temperature exceeds 170 ℃, the alloy will be permanently damaged.

Confirm the welding process. If the manual welding time is too long and the welding head directly contacts the resistor, it may cause deterioration of the internal welding interface.

Solution:

Choose low resistance models with higher pulse capability.

Increase the area of heat dissipation copper foil or add heat dissipation fins.

Strictly follow the reflow soldering curve (peak value of 245-260 ℃ is common, but EBW can withstand 350 ℃ for 30 seconds, and it is still recommended to follow standard J-STD-020).

PCB layout and soldering points

4.1 Pad Design (Land Pattern)

The PDF provides recommended pad sizes for EBWA and EBWB (see Land Pattern diagram in the document for details). Key parameters:

EBWA: The width of the solder pad is about 5 mm, and the length direction covers the copper terminal (5.6 mm) and extends 0.5-1 mm as a solder corner.

EBWB: Similarly, the pad width is 7.5 mm and the terminal length is 5.6 mm.

It is recommended to use a 4-wire Kelvin connection: the current terminal (large pad) carries the main current, and the voltage sampling terminal (small pad or independent wiring) is connected to the amplification circuit. Due to the fact that EBW resistors are two terminal components, Kelvin connections require shunting from the inside of the solder pad on the PCB, or using separate detection traces to lead out from the edge of the solder pad.

Common error: Directly connecting the two ends of the resistor with a wide copper sheet, causing the voltage sampling point to fall on the current path, resulting in the measured value including the contact resistance voltage drop.

Correct approach: Draw a thin wire from the inside of the resistor pad (near the resistor) to the operational amplifier, and avoid passing through high current paths.

4.2 Welding process

Reflow soldering: The EBW series can withstand 350 ℃ for 30 seconds or 250 ℃ for 10 minutes. The peak temperature of standard lead-free reflow soldering is about 245-260 ℃, far below the limit, so it has good compatibility.

Manual welding: Use a temperature controlled soldering iron (≤ 350 ℃) and control the welding time within 5 seconds to avoid heat transfer to the center of the resistor.

Directly welded to copper busbar: EBW's copper terminals can be welded to thick copper plates or busbars, suitable for ultra-high current (>200 A) scenarios. Suggest using a preheating platform for assistance.

4.3 Fault case: Resistance deviation after welding

Phenomenon: In mass production, some resistors have resistance values exceeding ± 1% of the specification after reflow soldering.

Reason: The PCB has a large thermal capacity or the peak value of the furnace temperature curve is too high (>350 ℃) and the time is too long, which causes the electron beam weld between the alloy and copper terminals to be affected by thermal stress, resulting in a slight increase in resistance.