How to choose solid-state relays when controlling a 230VAC heater using an STM32?

 If you're controlling a 230VAC heater using an STM32 microcontroller, you’ll need a solid-state relay (SSR) that can safely switch high AC voltage and be triggered by the STM32’s logic-level output (usually 3.3V or 5V). Here's a tailored SSR selection guide for your application:



 Recommended SSR Specifications for Your Case

ParameterRequirement
Load TypeResistive (heater)
Load Voltage230VAC
Load CurrentChoose SSR rated 1.5× to 2× heater current
Control Signal Voltage3.3V (from STM32)
Output TypeAC (Triac/SCR-based)
Switching FeatureZero-crossing detection (minimizes inrush)
Mounting TypePanel or DIN rail (based on enclosure)
IsolationOpto-isolated input (essential)
CoolingHeat sink if load current ≥10A

 Example SSR Models (Popular & Available)

SSR ModelControl VoltageLoad VoltageLoad CurrentNotes
Omron G3NA-220B5–24VDC75–264VAC20AReliable, widely used
Fotek SSR-25DA3–32VDC24–380VAC25ABudget-friendly, opto-isolated
Carlo Gavazzi RM1A23D253–32VDC24–280VAC25AIndustrial grade, robust

 STM32 Connection Example

Wiring the STM32 to the SSR:

  • STM32 GPIO (e.g., PA0) → SSR Input (+)

  • STM32 GND → SSR Input (−)

  • SSR Output terminals connect in series with the heater and 230VAC line

plaintext

STM32 3.3V GPIO ─────► SSR IN+
STM32 GND      ─────► SSR IN-

[ SSR OUT ] ────────► AC Heater
         │
       230VAC

Caution:

  • Do not connect AC components while powered.

  • Always isolate the STM32 side and use proper insulation.

  • Use fuses or circuit breakers for safety.

 Additional Tips

  • If SSR doesn’t trigger at 3.3V (some need 5V min), add a transistor or MOSFET driver between STM32 and SSR.

  • For higher power heaters (>1000W), consider SSR with heatsink.

  • Use zero-crossing SSRs to reduce switching noise and extend heater lifespan.

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