Voltage too low for relays


Im having troubles with my Arduino project.
I use an Arduino Mega 2560 for powering a relay board. With the digital output set to HIGH, the Arduino delivers 4.9 V, as normal. With the relay board connected, only 1.08V can be measured. This is always exactly the same value.
I decided to make the simplest setup possible, and set 1 relay at the time. Still had the same result.
The Arduino was powered by a 9V power supply, so delivering the voltage should not be a problem.
For powering the relay board, I just connected it to the power pins of the Arduino.

The code I used for the testing was this:

void setup() {
// put your setup code here, to run once:

void loop() {
// put your main code here, to run repeatedly:
digitalWrite(52, HIGH);
digitalWrite(52, LOW);
digitalWrite(50, HIGH);
digitalWrite(50, LOW);
digitalWrite(48, HIGH);
digitalWrite(48, LOW);

Anyone having an idea what the problem is?


Post your sketch to see how we can help.

Show us a good schematic of your circuit.
Show us a good image of your ‘actual’ wiring.
Give links to components.

You are probably taking more current from the pin than the Arduino can comfortably supply. How much current does the relay take to operate ?

At the moment, I can't find the exact specs of the relay board.
But I did use the same Arduino for powering 12 of these exact relays at the same time.
Powering one of them shouldn't be any problem at all.

Did you made any measurements?

I measured the outputs with the relays disconnected.
The output voltage is 4.9V as normal.

With the relays connected, there's always 1.08V at the relays. (measured to ground of course)

Why don't you measure the current being taken ?

1 Like

What kind of 9V power supply? Not one of those smoke detector batteries, is it?

The GND & VCC on the right are not there on the board I own...

Have you tried a different power source, such as the USB, as a 9V smoke detector has very limited current/capacity.

It's still not clear what power source you're using.
Also, it seems that you're using the 5V output of the Arduino board as the power source for the relay board. That's not going to work well; as soon as you start turning on a few relays, the voltage regulator on the Arduino will overheat and throw in the towel.

I've tried USB, since that didn't work I connected an adjustable adapter.
It's set at 9V now, and should deliver 0,6 amps. (more then enough)

But you don't actually know how much current the relays use

Why don't you measure it ?

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