AC SSR Heater Control

Question

Problem: AC SSR Heater Control. Solve this hands-on electronics task on EWskills.

Accepted Answer

1. Component Purpose

A heater in a temperature control system switches ON and OFF frequently — often hundreds of times per hour. Mechanical relay contacts would wear out quickly under this duty cycle.

A Solid State Relay (SSR) uses semiconductor switching (typically a TRIAC for AC loads) instead of mechanical contacts. This gives silent operation, no contact bounce, no mechanical wear, and extremely long life even with frequent switching.

Most AC SSRs use zero-cross switching — they turn ON only when the AC waveform crosses zero. This reduces EMI and inrush current on resistive loads like heaters.

Required: SSR · SPST-NO · AC Output · 5VDC input · 230VAC load · ≥5A · Safety approved

2. How to Find It on DigiKey

Go to DigiKey.com → Relays → Solid State Relays

Apply these filters:

Output Type → AC
Voltage - Input → Range includes 5VDC (e.g., 3–32VDC)
Voltage - Load → 240VAC or higher
Load Current → 5A or higher
Circuit → SPST-NO (1 Form A)
Part Status → Active

Tip: SSR input voltage is usually a range (e.g., 3–32VDC), not a single value. Make sure 5V falls within the specified input range.

3. Key Specifications & What They Mean

Specification	Required	Why
Relay Type	Solid State	No mechanical wear; long life.
Circuit	SPST-NO	Single normally-open output.
Output Type	AC	Switching 230VAC heater load.
Input Voltage	Includes 5VDC	Control signal from 5V logic.
Load Voltage	230VAC rated	Must handle mains voltage.
Load Current	≥5A	Heater draws 3A; margin for safety.
Temp Range	−40°C to +80°C	Panel-mount industrial conditions.
Safety Approval	UL/CSA/TUV	Required for mains switching.

Important: SSRs generate heat when conducting. For loads above 2–3A, always mount the SSR on a heatsink. Without it, the SSR can overheat and fail.

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 — AC SSR, 5V Input, 230VAC, ≥5A, SPST-NO

58. AC SSR Heater Control