Fotek solid-state relays (SSRs) are popular, compact, and highly reliable semiconductor-based switching devices, commonly used in temperature control, heating, and automation applications. The most common series, such as the SSR-DA (DC-AC) and SSR-AA (AC-AC), feature zero-cross switching to minimize interference.
1. Electrical Specifications
Input Control Voltage: Typically 3-32VDC or 4-32VDC (compatible with Arduino/TTL).
Load Voltage (Output): Standard: 24-380VAC; High Voltage (-H): 90-480VAC or 90-550VAC.
Rated Load Current: Models available in 10A, 25A, 40A, 50A, 75A, and 100A.
Control Current: Low input current, typically 3-25mA DC, or <7.5mA/12VDC.
Output Type: TRIAC or Thyristor (Zero Cross Trigger).
2. Environmental & Safety Features
Operating Temperature: -20°C to +80°C.
Overheat Protection: Many models include an internal protection circuit designed to turn off at 120°C.
Housing Material: Intensive ABS plastic.
Working Indicator: LED indicator for status (on/off).
Heat Sink Required: For loads over 5-10A, a heat sink is mandatory to prevent overheating and failure, as SSRs produce heat due to internal voltage drop.
Derating: For long-term reliability, it is recommended to derate the load current by 50% or more, especially with, or suspected, counterfeit units.
Zero Cross Function: Ideal for resistive loads (heaters) and some inductive loads; it minimizes EMI/EFI surges.
Types:
DA: DC Input / AC Output (Most Common).
AA: AC Input / AC Output.
DD: DC Input / DC Output.
VA: Variable Resistor Input / AC Output
