12. Motor Driver Bulk Capacitor Selection
1. Component Purpose
When a DC motor starts or the load changes suddenly, it draws a large burst of current. If the input supply cannot deliver this current fast enough, the 24V rail dips — which can cause the motor driver to malfunction, reset, or trigger undervoltage lockout.
A 100µF bulk capacitor placed near the driver input stores energy locally and releases it during these demand spikes, keeping the 24V rail stable. Aluminum electrolytic capacitors are ideal for bulk storage because they offer high capacitance in a compact size.
Required: 100µF · ±20% · Aluminum Electrolytic · ≥35V · SMD · −40°C to +105°C · RoHS
2. How to Find It on DigiKey
Go to DigiKey.com → Capacitors → Aluminum Electrolytic Capacitors
Apply these filters:
- Capacitance → 100µF
- Voltage Rated → 35V or higher
- Mounting Type → Surface Mount
- Part Status → Active
Tip: DigiKey may show separate sub-categories for "Aluminum - SMD" and "Aluminum - Polymer - SMD". Both are acceptable. Polymer types have lower ESR and longer life, but cost more.
3. Key Specifications & What They Mean
| Specification | Required | Why |
|---|---|---|
| Capacitance | 100µF | Enough bulk storage for motor startup surges. |
| Tolerance | ±20% | Standard for electrolytic capacitors. |
| Type | Aluminum Electrolytic | High capacitance at low cost for bulk storage. |
| Voltage Rating | ≥35V | Supply is 24V; 35V gives ~1.5× margin. |
| Mounting | Surface Mount | SMD for automated PCB assembly. |
| Temp Range | −40°C to +105°C | Standard for industrial motor driver boards. |
| RoHS | Yes | Compliance required. |
Tip: For electrolytic capacitors, always derate the voltage by at least 20–30%. Running at or near rated voltage shortens the capacitor’s lifespan significantly.
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