2-channel 5 V relay module: specs
A two-channel relay board for switching a separate circuit from a low-voltage control signal. If the relays are marked SRD-05VDC-SL-C on the body, each is a Songle relay with a 5 V coil and one changeover contact (COM, NO and NC), and the figures below apply. The board's input stage is not covered by a maker document.
Safety note. Signal side only. This page covers the control inputs and the coil supply. Anything connected to mains through the relay contacts, and the enclosure around it, must be wired by a qualified person.
Specs
| Spec | Value | Source |
|---|---|---|
| Relay coil voltage | 5 V DC (rated) | source SRD series coil table, p.1 |
| Coil current and resistance | 71.4 mA, 70 ohm +/-10% (0.36 W coil, code L); 89.3 mA, 55 ohm (0.45 W coil, code D) | source SRD series coil table, 20 C, p.1 |
| Pick-up and drop-out voltage | Pulls in at 75% of rated voltage or less; releases at 10% or more | source SRD series coil table, p.1 |
| Maximum coil voltage | 130% of rated voltage | source SRD series coil table, p.1 |
| Contact form | C (changeover: COM, normally open, normally closed) | source Ordering code and contact table, p.1; contact diagram, p.2 |
| Contact rating (AC) | 7 A, 10 A or 15 A at 250 VAC depending on the version; the 15 A 250 VAC certification covers the NO contact only. Check the rating printed on the relay body | source Contact table, p.1; certification table, p.2 |
| Operate and release time | 10 ms or less each, at rated voltage | source Characteristics table, p.1 |
| Insulation | 100 Mohm at 500 VDC; 1500 VAC for 1 minute between coil and contacts; 1000 VAC for 1 minute between open contacts | source Characteristics table, p.1 |
| Operating temperature | -40 C to +85 C (a +105 C version is also listed) | source Characteristics table, p.1 |
Power
| Value | Source | |
|---|---|---|
| Supply | 5 V DC to the relay coils | source SRD series coil table, p.1 |
| Current | About 71.4 mA per energised relay (0.36 W coil), so about 143 mA with both on, plus the board's input stage and LEDs (not documented) | source SRD series coil table, p.1 |
Pinout
We don't publish a pin table for this part: no official source we could verify gives one. Check the labels printed on your module, and see the notes below.
No maker document covers this board's header, jumper or input circuit. Use the labels printed on the board. The relay's own contact layout (COM, NO, NC) is in the Songle sheet, p.2.
Build with it
Project ideas for the 2-channel 5 V relay module. Each link opens Soldr with the prompt filled in; Soldr assigns the pins, checks power and shows how to wire every part.
- Find out whether your relay board switches on LOW or HIGH: Nothing is connected to the relay contacts. Power the board from the Uno's 5 V and GND, then touch the first input pin (use the label printed on the board) to GND and then to 5 V with a jumper wire; the click, any indicator LED and the meter's continuity between COM and NO show which level switches it. Before driving the input from an Uno pin, measure the current it draws on the meter's lowest current range: 40 mA is the ATmega328P's absolute maximum per pin (Microchip DS40002061A, section 29.1), a stress limit, not a working current, so stay well below it. Learning project.
- Temperature-switched 12 V fan: The relay switches only the fan's 12 V DC supply, never mains. The Songle sheet gives AC contact ratings only, so check the DC rating printed on the relay body against the fan's current from its label. Fit a 1N4007 across the fan (band to +12 V) to absorb the turn-off spike.
- Two buttons for two 12 V LED strips: Each relay switches one strip's +12 V supply. With no colour controller, join each strip's R, G and B wires to 12 V ground for white light, and the relay switches the +12 V wire. The 12 V 2 A adapter must cover both strips' current from their labels. Both coils on take about 143 mA from the 5 V side, so check the Uno's 5 V budget when it runs from USB.
Common mistakes
- Wiring mains to the relay terminals without the training to do it safely: anything on mains must be wired by a qualified person. This page covers the signal side only (no source: safety rule)
- Powering both relays from a board's 5 V pin without checking the budget: each coil takes about 71.4 mA, so both together take about 143 mA before the input stage (source)
- Assuming the input is active-high: the board's trigger level is not in any maker document, so test it with a jumper wire before writing code, as in the first idea below (no source: test step)
Not covered by the official source
- The board's input stage (optocoupler part, transistor, resistor values) is not in a maker document, so the trigger level, input current and 3.3 V behaviour are not given here.
- The Songle sheet gives AC contact ratings only; for DC loads use the rating printed on the relay body.
- Coil power depends on the marking: SRD-05VDC-SL-C is the 0.36 W coil (71.4 mA, used above); SRD-05VDC-SD-C would be the 0.45 W coil (89.3 mA).