Arduino Mega 2560 + Arduino Ethernet Shield 2 power requirements to drive relay

Other Hardware General Electronics
1

Hello,

I have an Arduino Mega connected to
Ethernet shield 2
two DM542T stepper driver
two relays
4 DS18B20 sensors.

The temperature sensors and relays are connected to an external 5v supply, and arduino with 12v(both are from old router or other ac adapter, rated close to 1A).

The stepper drivers are powered by 48v power supply, but the inputs are (DIR, ENABLE, PUL) are connected to arduino i/o pins.

What I observed was I could trigger one relay fine, but when I added second, it work if I connects my laptop through USB cable as well as 12v supply. When I remove the USB cable and power alone with 12V, the relay doesn't trigger. Does it clearly indicate not enough power to enable the relay?

I read many posts related to this, and though the amazon reviewer suggest there is a way to isolate the relay coil from Arduino power, this relay doesn't have a jd-vcc jumper clearly marked, and I didn't attempt but use common ground between +5v supply and arduino.

This is my first Arduino project and any help on identifying the cause or any suggestions are highly appreciated.

Thanks.
bsr

2

Hi..

please post a circuit diagram of your connections.

  1. Can you turn on one relay at a time but not both ?
    2.Try turning one on with the other off and vice versa.
  2. Measure the voltage across both relays when they are triggered
3

Thank you. I measured the voltage as you suggested and found it's below 2v. So, tried replacing the power supply, and everything works so far.

4

Glad you solved it!