5v relay breaks, twice!


I’m doing a first Arduino project using a Arduino Yun and 2 5V relays to control my window shutters.

Everything was working for a while (2-3 weeks), even built a webapp to control everything, until after some time the relay seems to have broken.
I bought a new one and now it broke again in the same way again after some weeks.

Relay details :

When connecting the relay with LOW - digitalWrite(relay1Pin, LOW), I hear the relay click and indication LED is ON.
However without any load and with a multimeter I can measure the connection seems to remain between COM1 and NC1 (while it should switch to COM and NO).

The load is 220V but should even be below 1A, the relay should be fine up to 10A.
Could I have connected something wrong? Or might I just have gotten 2 broken items?
Should I try ordering a similar relay from a different brand?

Attaching a picture of the electrical wiring, I can write the connections in detail if needed.

Thanks, Hannes

Please supply a circuit diagram. Freehand on a sheet of paper and photographed will do.


Provide wiring diagram of your system. In the photo one of the relays appears to use all 3 connections but the other appears to use only 2. As I read it, the left relay is acting as a master On/Off switch and the right one is acting as a change-over switch, with input line being fed from the master switch. From your description of the fault it sounds like you have contacts welding closed. It could be that the motor current during start or stall is exceeding the relay capacity. Many relays rated at 10amps are the figment of the manufacturer's imagination and are really unsuitable for such loads. The ratings are generally specified for resistive loads only, if you have an inductive load such as a motor the demand on contact performance increases dramatically. Of course your shutter motors could also be defective

Indeed, the left relay is acting as on/off, the right relay is determining the direction up/down for the tubular motor I am connecting it with.

Eg specs for similar motor as I have : http://www.produktinfo.conrad.com/datenblaetter/625000-649999/646762-an-01-ml-ROHRMOTOR_20NM_SW60_RM20MM_de_en_fr_nl.pdf

p22 : Item No. Motor cable wire colour Function 1 Black Direction of rotation 1 2 Brown Direction of rotation 2 3 Blue Neutral conductor 4 Green/yellow Earth

These are the connections :

Arduino GND > Relay-GND Arduino GND > Relay-GND Arduino pin 8 > Relay-IN2 Arduino pin 9 > Relay-IN1 Arduino 5V > Relay-VCC

AC-blue > Motor-blue AC-gnd > Motor-gnd AC-brown > Relay2-COM

Relay2-NO > Relay1-COM Relay1-NC > Motor brown Relay1-NO > Motor black

Arduino Code - fyi

void setup() { pinMode(ledPin, OUTPUT); // for LED (pin 13) pinMode(buttonPin, INPUT_PULLUP); // to ground (pin 2) pinMode(relay2Pin, OUTPUT); //output > relay 2 (pin 8) pinMode(relay1Pin, OUTPUT); //output > relay 1 (pin 9) // relay testing pinMode(highPin, OUTPUT); // (pin 10) pinMode(lowPin, OUTPUT) ; // (pin 11)


void setRelays(){ switch (windowShutterMovingDirectionState) { case 0: // stop digitalWrite(relay2Pin, HIGH); // windowshutter off (default) digitalWrite(relay1Pin, HIGH); // windowshutter goingdown (default) break; case 1: // going up digitalWrite(relay2Pin, LOW); // windowshutter on digitalWrite(relay1Pin, LOW); // windowshutter goingup break; case 2: // going down digitalWrite(relay2Pin, LOW); // windowshutter on digitalWrite(relay1Pin, HIGH); // windowshutter goindown break; } }

When I test putting the (in picture, orange) cable from pin 8 to pin 11 the relay clicks and led goes on but relay 1 connection does not change from NC to NO.

I have not installed this motor myself so have to check for the exact type. However the cables that came installed with the motor were very thin (I think 0,75mm² stranded wire), so I was expecting a 10A relay to work.

If the motor would be 1A average, what inductive load could be suspected? Can you suggest other relay types better suited this?

Thanks, Hannes

Motors have a huge inrush current which may be straining the relay.

Try a relay that can handle 20 amps.


Appears you are powering the relay coils from the Arduino's 5V regulator, 2 coils at the same time will draw over 140 mA, not good, should have a separate 5V, at least 300 mA supply for the coils.

Thanks all for the feedback. Ill order and try something like this then : http://eud.dx.com/product/5v-30a-c-type-opto-isolated-relay-module-blue-844214657#.VwNvKqSLSUk

I will get 2 so everything in the circuit is in theory safe up to 30A. I'll also look into providing a seperate 5V power.

Just for my understanding.. is it more the relay who closes the circuit that is wearing the most? Wondering because also the supplied cables are very thin. So this might also work?

// start digitalWrite(relay1Pin, LOW); // 10A relay delay(50); digitalWrite(relay2Pin, LOW); // 30A relay (on/off)

// stop digitalWrite(relay2Pin, HIGH); // 30A relay (on/off) delay(50); digitalWrite(relay1Pin, LOW); // 10A relay

I hestitate to say it (in case I anger the fairies) but I have a relay controlling my 230v fridge. I think the current one is rated at 16 amps (for a 60w fridge !) and it has performed faultlessly for a long time. The original smaller relay did not last long. The synchronous motors in fridges draw an enormous current briefly at startup.

It's a long time since I built the circuit and I also have a thing which I believe is called a snubber across the switch connection. I don't remember the part number or even where I got the idea for it.


Also motors are massively inductive loads, so you need to snub any switch or
relay switching them to avoid big sparks damaging the contacts (or welding
them together as here). Google “snubber network”