Seeed Relay Selection Guide

We have released various types of relays on our website. You may find it difficult to make a choice. We feel you pain, let's talk about what's the difference between all those relays, and what's the advantage or disadvantage among them.

For all the relay in our bazaar, please click bazaar relay tag to check.

Before the start, let's check the seeed relay quick selection diagram.

For more detail, please refer to the following table, perhaps, all you need is just a table.

Name Thumbnail Operate voltage Input current Rated load Contact resistance Insulation resistance Operate time Release time Input interface Type Click to buy
Grove - Relay 3.3V-5V 100mA 5A@250VAC
@6VDC 1A
100MΩ 10ms Max. 5ms Max. Digital Electromechanical Buy Now
Grove - SPDT Relay(30A) 5V 185mA 30A@250VAC
100mΩ Max. 100MΩ Min.@500VDC 15ms Max. 10ms Max. Digital Electromechanical Buy Now
Grove - 2-Channel SPDT Relay 5V 90mA 10A@250VAC
100mΩ Max. 100MΩ Min.@500VDC 10ms Max. 5ms Max. Digital Electromechanical Buy Now
Grove - 4-Channel SPDT Relay 5V 90mA 10A@250VAC
100mΩ Max. 100MΩ Min.@500VDC 10ms Max. 5ms Max. I2C Electromechanical Buy Now
Grove - Solid State Relay 3V-5V 16mA Min.
20mA Typ.
50mA Max.
4A@220VAC 1000MΩ 10ms 10ms Digital Solid State Buy Now
Grove - Solid State Relay V2 4V-6V 2A@100VAC to 240VAC 1000MΩ Min.@500VDC ½ of load power source cycle +1 ms max ½ of load power source cycle + 1 ms max Digital Solid State Buy Now
Grove - 2-Channel Solid State Relay 4V-6V 2A@100VAC to 240VAC 1000MΩ Min.@500VDC ½ of load power source cycle +1 ms max ½ of load power source cycle + 1 ms max Digital Solid State Buy Now
Grove - 4-Channel Solid State Relay 4V-6V 2A@100VAC to 240VAC 1000MΩ Min.@500VDC ½ of load power source cycle +1 ms max ½ of load power source cycle + 1 ms max I2C Solid State Buy Now
Grove - 8-Channel Solid State Relay 4V-6V 2A@100VAC to 240VAC 1000MΩ Min.@500VDC ½ of load power source cycle +1 ms max ½ of load power source cycle + 1 ms max I2C Solid State Buy Now
Grove - 2-Coil Latching Relay 5V 1A@125VAV
50mΩ Max. 1000MΩ@500VDC 4.5ms Max. 3.5ms Max. Digital Electromechanical Buy Now
Grove - Dry-Reed Relay 5V 0.1A@100VAC
150mΩ Max. 100MΩ @500VDC
1000MΩ @100VDC
1ms Max. 0.5ms Max. Digital Reed Relays Buy Now
Table 1.Seeed Relay Parameter

You can click the following button to download the zip file of both the diagram and the table:


A relay is an electrically operated switch, the relay opens when the two contacts are disconnected, and the relay turns on when the two contacts touch.

Figure 2. Relay Contacts

Each contact connects to an input or output terminal. The input terminal is called Pole, and the output terminal is called Throw. According to the number of terminals, the relay is divided into several types. which is SPST,SPDT,DPDT, and so on.

SPST(Single Pole Single Throw):
SPST is the simplest relay, you can consider it as a button. This 'button' is normally open, when the trigger signal comes, the pole contact will connect to the throw contact, we call it close. It is great for applications that need only an on or off state. A typical representative of SPST is our Grove - Relay

Figure 3. SPST Relay

SPDT(Single Pole Double Throw):
SPDT relay is ofen called A/B swicth, as you can see in the figure 3, there are two throws, this kind of relay is great for selecting between two options.

Figure 4. SPDT Relay

You may find that these two throws are called NC and NO respectively, and the pole is called COM. NC means normally connected, NO means normally open. Which means if there is no trigger signal, the NC terminal will be connected to the COM terminal, once the trigger signal comes, the NC terminal will be disconnected and the NO terminal will be connected to the COM termianl. For instance, you can refer to our Grove - 2-Channel SPDT Relay.

Grove - 2-Channel SPDT Relay
Figure 5. Grove - 2-Channel SPDT Relay

We only have SPST and SPDT relays in our website now, if you want to check other types of relays please refer to the relay page by NATIONAL INSTRUMENTS.

Latching Relay

Latching Relay is a relay that is set (ON) or reset (OFF) by the input of a pulse voltage. Even after the input voltage is interrupted, this relay maintains its set or reset condition until it receives the next inverting input. It is also called a keep relay. Conversely, a non-latching relay maintains its state only while being actuated, most of relays in our website is non-latching relay except the Grove - 2-Coil Latching Relay.

Types of Relays

Although there are more than a dozen relays in our website, in general, there are only three types: Electromechanical Relay, Solid State Relay and Reed Relay. You can see the classification information in the last column of Table 1.

Electromechanical Relay


Most relays in our bazaar are Electromechanical Relay. Normally a Electromechanical Relay is consisted of coils, armatures and contacts.

Electromechanical Relay
Figure 6. Electromechanical Relay

When the coil is energized, the induced magnetic field moves the armature, which opens or closes the contact.

Advantage and Disadvantage


  • Able to withstand large inrush currents
  • High mechanical structure reliability, not susceptible to external electromagnetic environment
  • Cheap and cost-effective
  • Relatively speaking, it can carry high voltage, high current load


  • Electromechanical relays are slower than other types of relays, typical switch and settle in 5 to 15 ms
  • Larger package sizes, not suitable for size sensitive occasions
  • In general, Electromechanical relays have a shorter life than other types of relays due to mechanical wear

Solid State Relays


Solid State Relays is also known as SSR, which is an electronic switching device that switches on or off when a small external voltage is applied across its control terminals. Solid state relays typically use semiconductor devices to switch the conduction and disconnection of high voltage loads. Normally a Solid State Relay is consisted of a LED driver and a photosensitive MOSFET. When the trigger signal comes the LED light up to actuate the photosensitive MOSFET, then the high voltage circuit will be turned on.

Solid State Relay
Figure 7. Solid State Relay

Advantage and Disadvantage


  • Fast switching speed, the switching time is dependent on the time required to power the LED on and off—approximately 1 ms and 0.5 ms. For instand the G3MC202p serial SSR we use is ½ of load power source cycle +1 ms.
  • Totally silent operation, almost no noise
  • No physical contacts means no sparking, allows it to be used in explosive environments, where it is critical that no spark is generated during switching.
  • Increased lifetime, even if it is activated many times, as there are no moving parts to wear and no contacts to pit or build up carbon
  • Compact, thin-profile SSR of monoblock construction with an all-in-one lead frame incorporates a PCB, terminals and heat sink, which is much smaller than mechanical relays, and can integrate more channels
  • Not susceptible to physical shock


  • Contact resistance is relatively large, usually above 100 ohms, which will generat more heat, so it need to be used with fan heat.
  • High cost and low cost performance
  • Only works for AC laod


Please note that some kind of solid state relays support DC load, but all the solid state relays currently sold by seeed do not support DC load.

Reed Relays


Reed relays are switches that use electromagnets to control one or more reed switch. The contacts are of magnetic material and the electromagic acts directly on them without requiring an armature to move them. Sealed in a long, narrow glass tube, Fill the glass tube with inert gas so that the contacts are protected from corrosion.

Reed Relay
Figure 8. Reed Relay

As shown in Figure 7, there is no axial magnetic field generated when there is no trigger signal excitation, the reed blade will be disconnected because of the rigidity. When the signal is triggered, a transverse magnetic field will be generated and the reed will be magnetized. One contact turns N pole and the other turns S pole, they will be connected.

Advantage and Disadvantage


  • Low power consumption, small size
  • Because it is sealed in an inert gas, very little affected by environmental factors such as temperature and humidity , high environmental adaptability
  • Switching speed is fast, about 10 times higher than electromechanical relay


  • Low load voltage and low current
  • Susceptible to inductive loads


If you need to use reed relay with an inductive load (such as a motor), you need to add a protection circuit between the relay and the load.

Special Function Relays

In addition to the typical relays described above, we have several special-function relays in our website.

1.Relay Shield v3.0

We also provide a relay shield for arduino, this shield integrates four mechanical relays, can carry 8A, 30V load.

2.Heelight Relay

You can control the relay through a sound command, isn't it interesting!?

3.315MHz Codec-Adaptive Wireless Relay

A wireless relay is a codec-adaptive RF receiver with single channel relay.


Tech Support

Please do not hesitate to contact techsupport@seeed.cc if you have any technical issue. Or submit the issue into our forum.