AC Load Relay Selection

Question

Problem: AC Load Relay Selection. Solve this hands-on electronics task on EWskills.

Accepted Answer

1. Component Purpose

The controller runs on low voltage (3.3V/5V logic), but the lamp runs on 230VAC mains. Direct connection would destroy the controller and create a lethal shock hazard.

A relay provides complete electrical isolation. The low-voltage side energizes the coil; the high-voltage side switches the lamp through mechanically isolated contacts. The two sides share no electrical connection.

Required: General Purpose · 12VDC coil · SPST-NO or SPDT · ≥5A contacts · 230VAC rated · Non Latching · Through Hole · Safety approved

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

Important: Always check the relay datasheet for the maximum switching voltage — not just the current rating. A relay rated 10A at 30VDC may NOT be rated for 230VAC. Look for 250VAC (or higher) in the AC switching specifications.

3. Key Specifications & What They Mean

Specification	Required	Why
Coil Voltage	12VDC	Must match driver circuit supply.
Contact Form	SPST-NO or SPDT	Only NO switching needed; SPDT also works.
Contact Current	≥5A	Load is 2A; ≥5A gives derating margin.
Switching Voltage	230VAC rated	Contacts must be rated for mains voltage.
Coil Type	Non Latching	De-energizes when control is removed.
Mounting	Through Hole, PC Pin	Standard PCB relay mounting.
Temp Range	−40°C to +85°C	Indoor industrial panel conditions.
Safety Approval	cURus / UL	Required for mains voltage switching.

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

5. Filtered DigiKey Link

➡ View Matching Parts — 12VDC Coil, SPST-NO/SPDT, ≥5A, 250VAC, Through Hole

54. AC Load Relay Selection