enter image description hereI have a 8 relay module that should use not more than 20 mA per relay. Altough when measuring it asks around 70. If I use 6 relays, that would be more than an Arduino Mega can give. (I already lost 1 arduino here.)

How this is possible..?

  • What are you measuring? The input pins will be the low current pins, however the power supply pins will take more (and you can power those without going through the arduino) – ratchet freak Sep 28 '18 at 16:31
  • Someone told me to give 5v en GND to the relais module not from arduino but from another source. Will try that. – Dirk E Sep 28 '18 at 16:43
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    I don't see why and Arduino mega can't supply 420mA from the 5V pin. It's also below the USB limit of 500mA. – Gerben Sep 28 '18 at 18:24
  • please add a link to where you bought the relay module .... also add the schematic of the connections between the arduino and the relay module – jsotola Sep 29 '18 at 5:41
  • Hello Gerben, it should be indeed possible for the mega but in practice it seems that the relays are asking more than the specs are telling.. Jsotola: will look up the fritzing – Dirk E Oct 1 '18 at 10:10

Most of Arduino relay modules have a relay and a supporting circuit. The circuit connects the VCC line to relay coil if signal line is HIGH. Some relays have it conversely, they disconnect if signal is HIGH and hold the coil if signal is LOW.

Your relays need VCC which you can supply for 8 relays from 5 V pin of Arduino. This pin is connected over regulator to power supply of the board so it is limited only by power supply and regulator parameters. The power doesn't go over MCU.

The signal pins of individual relays should be connected to digital pins of Arduino. The signal pins don't draw much current since they only signal a state to the circuit of the relay module.


it is solved by giving the relay module power with external transfo. Not by arduino

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