Doing a project using an Arduino Due and I need to trigger some relay circuits, so I'm using these relay components: https://pdf.voron.ua/files/pdf/relay/JQC-3F(T73).pdf (the 3V version). I'm connecting the coil pins on the relay to the 3.3V pin and GND pin on the Arduino.
I've tested 3 times and the relay always works for a second and then instantly breaks (I then can't get the relay to work again when I disconnect and reconnect the circuit). Is this because 3.3V is too high for the 3V relay and it's blowing the component? Or should the relay in theory work fine with 3.3V, in which case something else is wrong with my setup instead?
3.3V is only 10% over and it should be OK. ...Usually the specs will give you a minimum & maximum.
And, usually there is a transistor or MOSFET driver and there is a little voltage drop across the driver so often you don't get the full supply voltage..
The 3.3V power from the Arduino can drive the relay, but an I/O pin can't put-out enough current without a driver circuit.
There should also be a reverse "flyback diode" across the coil because it will generate a short-duration high-voltage when turned-off. That voltage won't hurt the relay but it can blow the connected circuitry.
You should use a 5volt relay module, and power it from the 5volt supply of the Due.
Many 5volt relay modules can be controlled by a 3.3volt-logic pin.
Leo..
Thanks for the responses all. I didn't know about the flyback issue. If I understand right, are you saying it's possible to buy relays that have the flyback diode already built in across the coil? If so, do you have any recommendations for which ones to get?
As for using a 5V diode, that won't work with my current plans for the project unfortunately - I was only using the 3.3V pin as a quick test because I hadn't used the relay component before and wanted to check how it works. In the actual project I want to control the relays from some of the digital logic pins of the Arduino Due which are all 3.3V.
This is a diagram of the intended circuit. Essentially when a certain set of inputs are read from the RFID readers, the Arduino needs to trigger the relays to turn on the LEDs. This setup worked fine for me before I added the relays (ie. when I just connected the digital pins directly to some lower voltage LEDs), but I can't get it to work now I've added the relays into the mix.
Do you understand what everyone is telling you to do?
You need to use a circuit like @FernandoGarcia is showing with VCC connected to an external 3.3V power supply
Many thanks for this diagram, this does make sense to me. Out of curiosity why is the external power supply needed though? What would be the issue with just removing the transistor and input from that circuit and using an arduino logic pin in place of the VCC?
Ah so the current is too low, thanks! Does this mean that I could use the 3.3V on in place of an external power source since that has a higher current of 800mA, or is that still too low? I'm not sure where to find the required current for the relay module
Yeah this looks really useful - is this basically a higher level module that has most of the elements of the circuit Fernando described above already built into it? If so, where can I get one?
