6. Motor Current Shunt Resistor Selection
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