The G3MB-202P is a low-cost subminiature PCB-mounting solid state relais capable of switching AC loads of up to 2A.
This SSR can be an excellent choice for switching light AC loads like lamps or fans. With its limit of 2A, at 220V this allows switching loads of less than 440W. Considering tolerances and current spikes at turn-on, you should not use this SSR for loads in excess of 200W.
Overview
The G3MB-202P is a widely used SSR for switching AC loads in a very small form factor. Its relatively low switching capabilities of just 2A make it a choice for switching very light loads such as lamps or small fans.
It is often used with breakout boards that can use a single SSR, or combine two, four, or even eight SSR on one board.
This SSR is designed to switch AC loads. You cannot switch DC loads with it.
Power Requirements
The SSR requires a basic 5V power supply (DC+/DC-) and takes 12.5mA per SSR. Triggering takes another 2mA per SSR (CH1, CH2, etc.).
Low/High Level Trigger
On breakout boards, the SSR can be operated in two different ways:
- High Level Trigger: opposite behavior: the trigger input must be high in order for the SSR to be on.
- Low Level Trigger: when the trigger signal is low (0-2.5V), the SSR is on. When the trigger signal is high (3V or above), it is off.
Regardless of trigger type, when you cut the power supply to the board, the SSR(s) turn off (become non-conductive): even a low level trigger board with 0V at its trigger pin will cut the load once the power supply is removed from the board.
Microcontroller-based projects can work well with both trigger types. You may be able to tweak overall power consumption though:
When the load you want to control is typically turned on most of the time, a low level trigger may save 2mA per SSR by keeping the SSR in on-state via 0V. When the load is turned off most of the time, it is the other way around.
Wiring
Breakout boards come with screw terminals on both sides of the board.
Power Supply And Triggering
One side controls power supply and the SSR state:
| Terminal | Description |
|---|---|
| DC+ | 5V in (4-6V DC) |
| DC- | GND |
| Ch1 | logic level for first SSR |
| Ch2 | logic level for second SSR |
| Chx | one Chx pin for each additional SSR |
Breakout boards with four or more SSR often provide both screw terminals and header pins for these connections:
G3MB-202 comes in 5V, 12V, and 24V versions. Double-check the markings on the SSR to ensure you are using the correct version and supply voltage. This article covers the 5V version.
The trigger pin takes a logic level:
- Low: 0V-1.5V
- High: 2.5V-5V
Depending on the board type, a low level trigger requires a low level to turn the SSR on, whereas a high level trigger requires a high.
Breakout boards work well both with 5V Arduinos and 3.3V ESP8266/32. Just make sure you supply 5V to DC+/DC-. The trigger pins can then be directly connected to a GPIO and require only 2mA.
Switching Loads
The screw terminals on the other side control the AC load:
| Terminal | Description |
|---|---|
| SW1 | two screw terminals become conductive when first SSR is turned on |
| SW2 | two screw terminals become conductive when second SSR is turned on |
| SWx | two screw terminals become conductive when additional SSR is turned on |
Zero Crossing
Zero Crossing is a technique by which a SSR switches an AC load when the alternating voltage crosses 0V, minimizing the stress on the components.
G3MB-202P does not support Zero Crossing whereas G3MB-202PL does.
Trigger Pins
The trigger pins (Ch1, Ch2+, …) can be connected directly to a GPIO.
These input pins are compatible with both 3.3V and 5V and do not require a level shifter. With just 2mA, they can easily be serviced by a GPIO output pin: they essentially just drive the LED in the internal optocoupler.
AC Load(s)
The load side (that connects the AC load that you want to switch) is using dangerously high AC voltage. Always take extreme care and use proper insulation.
The PCB is physically separated into the low voltage control part and the high voltage switching part. The SSR internally uses optocouplers to electrically separate both sides.
The screw terminals on the load side must be tighly secured. These wires are connected to dangerous AC current. Make sure these wires cannot be pulled or slip out of the terminals in any other way.
Typical Wiring Scenario
The SSR can be destroyed when you exceed the allowable input voltage (the datasheet states an allowable input voltage of 4.0-6.0V).
Here are your safe power options for connecting DC+ and DC-:
- USB Power: if you power your microcontroller project via USB, the voltage is guaranteed to be within safe levels. Connect DC+ directly to USB 5V+ and bypass the internal microcontroller voltage regulator (if present).
- External Power (4.0-6.0V): when using an external power supply, if this supply is guaranteed to be in the 4.0-6.0V range, you can again directly connect DC+ to your external power.
- External Power (>6.0V): if your external power exceeds 6V (or you cannot guarantee safe voltage levels), connect DC+ to the 5V pin on your microcontroller, and use its built-in voltage regulator to ensure a proper input voltage.
Some microcontroller boards (especially ESP8266 D1 Mini) come with weak voltage regulators that may not be able to provide the currents required. When you experience unexpected reboots, you may not be able to run DC+ off the 5V pin. In this case, use an appropriate external power supply or a separate distinct voltage regulator.
Data Sheet
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(content created Jul 31, 2024)