55. DC Motor Relay Selection
1. Component Purpose
The controller needs to turn a 12V DC motor ON and OFF. A relay isolates the motor’s high-current circuit from the low-current controller, and provides a clean mechanical ON/OFF switch.
DC loads are harder on relay contacts than AC loads. AC current crosses zero 100/120 times per second, which helps extinguish the arc when contacts open. DC current has no zero-crossing, so the arc persists longer and erodes contacts faster. This is why adequate current margin is important.
Required: General Purpose · 12VDC coil · SPST-NO or SPDT · ≥5A contacts · DC rated · Non Latching · Through Hole
2. How to Find It on DigiKey
Go to DigiKey.com → Relays → Power Relays
Apply these filters:
- Coil Voltage → 12VDC
- Contact Form → SPST-NO (1 Form A) or SPDT (1 Form C)
- Contact Rating (Current) → 5A or higher
- Coil Type → Non Latching
- Mounting Type → Through Hole
- Termination Style → PC Pin
- Part Status → Active
Tip: When checking the datasheet, look for the DC contact rating specifically. Many relays are rated 10A at 250VAC but only 5A or 3A at 30VDC.
3. Key Specifications & What They Mean
| Specification | Required | Why |
|---|---|---|
| Coil Voltage | 12VDC | Matches driver supply. |
| Contact Form | SPST-NO or SPDT | Only NO switching needed. |
| Contact Current | ≥5A | Motor draws 3A; DC arc needs extra margin. |
| Switching Voltage | 12VDC rated | Must be rated for DC switching. |
| Coil Type | Non Latching | Standard ON/OFF control. |
| Mounting | Through Hole, PC Pin | Standard PCB mount. |
| Temp Range | −40°C to +85°C | Industrial conditions. |
| Safety Approval | cURus or equiv. | Product certification requirement. |
4. Selecting a Safe, Production-Ready Part
The filtered list will show 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