Motor Current Shunt Resistor Selection

Question

Problem: Motor Current Shunt Resistor Selection. Solve this hands-on electronics task on EWskills.

Accepted Answer

1. Component Purpose

The motor draws up to 2A. To detect overload, the controller needs to measure this current. A shunt resistor in the current path creates a small voltage drop proportional to current (V = I × R). The controller’s ADC reads this voltage to calculate current.

At 0.1Ω and 2A: voltage drop = 0.2V (readable by most ADCs). Power dissipated = I² × R = 4 × 0.1 = 0.4W. So the resistor must be rated ≥1W for safe margin.

Required: 0.1Ω · ±1% · ≥1W · 2512 · Current Sense · ±100ppm/°C · −55°C to +125°C · RoHS

2. How to Find It on DigiKey

Go to DigiKey.com → Resistors → Chip Resistor - Surface Mount

Apply these filters:

Resistance → 0.1 Ohms (100 mOhms)
Tolerance → ±1%
Power (Watts) → 1W
Package / Case → 2512
Temperature Coefficient → ±100ppm/°C or better
Part Status → Active

3. Key Specifications & What They Mean

Specification	Required	Why
Resistance	0.1Ω	Gives 0.2V drop at 2A — ADC readable.
Tolerance	±1%	Current accuracy depends on resistor accuracy.
Power Rating	≥1W	Actual dissipation is 0.4W; 2× margin needed.
Type	Current Sense	Designed for low-ohm, stable sensing.
Package	2512	Large enough to dissipate 0.4W safely.
Temp Coefficient	±100ppm/°C	Low drift keeps readings stable when hot.
Temp Range	−55°C to +125°C	Standard industrial range.
RoHS	Yes	Compliance required.

Tip: Metal element resistors generally have better temperature stability than thick film for current sensing applications.

4. Selecting a Safe, Production-Ready Part

The filtered list will show many matching parts. Before you pick one, check: Is it Active? Is stock available? Is the manufacturer reputable? Is a datasheet available?

Full checklist: How to Select a Safe, Production-Ready Component — EWskills Guide

5. Filtered DigiKey Link

➡ View Matching Parts — 0.1Ω, 2512, ±1%, ≥1W, Current Sense

6. Motor Current Shunt Resistor Selection