I have an Arduino mega that is being used to control relays and ultrasonic sensors. The relays that I am using is a 4 DPDT Signal Relay Module Model: D-256 Series and the other is a 4 channel Single pole Relay for Arduino. I am only using 3 channels of each relay. At any given time I only output to 2 channels from each relay at a time. I tested the relay to ensure they worked with the Arduino and they ran fine.

Once I connected the Ultrasonic sensors to the board as well, the board would not power and the voltage regulator got extremely hot. I would assume the total current draw was too high from the outputs and VCC of the Arduino.

I think that if I take my 9V battery and run it through a voltage regulator 7805 then I can run the VCC power of the relays with the battery instead of the VCC from the Arduino. This would result in me only running a VCC to the 4 ultrasonic sensors, the triggers for the ultrasonics from the Arduino, and the output signals fora maximum of 2 channels per relay board resulting in 4 relays. Most of the time it is only 2 relays.

Would I be able to power the relay boards VCC with the 9V running through a 5v regulator instead of the arduino so that I can reduce the current running through the Arduino?

  • yes, that will work as you think. you'd be better of with a buck regulator though. a lot better off...
    – dandavis
    Oct 25, 2018 at 16:03

2 Answers 2


What could be going on here apart from what @JRobert has suggested, is, LM7805 could be generating a lot of heat loss.

4 X Ultrasonic sensors (SR HC-04) would draw 60mA.

2 X Relays (SRD-05VDC-SL-C) would draw 71.4 X 2 i.e 142.8mA.(Depends on from where you signal it) The Arduino mega would draw anywhere between 200 - 500 mA.(even more)

The amount loss you will have is (9-5)V * (202.8 + 250)mA i.e. around 2 Watts. This is a lot of heat. I'm not even sure the LM7805 would be able to handle it.

Solution: use a switching regulator like the one mentioned here: https://electronics.stackexchange.com/questions/21131/efficient-low-power-regulation-i-e-9-5-volts

  • This is what I was thinking. The relays and sensors pulled in pulled too much current through the voltage regulator. My current setup that I have and it seemed to work was put a 9V battery that runs through a regulator to power the VCC of the relays. I also have a seperate battery pack that runs the Arduino. Now the only things that run out of the output terminals from the Arduino are the sensors and the output signals for the relays.By removing the VCC load from the Arduino, I am no longer overloading the voltage regulator on the board. It stayed cool while I was running yesterday Oct 26, 2018 at 12:16

It sounds like a power-to-ground short circuit, either a fault in the Ultrasonic sensor or in the connection to the Arduino.

Check your connections, and if you have an Ohm-meter, check the resistance between the sensor's power and ground pins.

Current consumption is a function of the device being powered, not of the power-supply, unless the supply lacks the capacity to provide as much current as the device needs.

Note that 9v batteries (the small brick aka a "transistor battery") is not well suited to supplying much current and probably will not power your Mega, or not for long, anyway. They are much better suited for long-term powering of very low current devices, such as a smoke detector.

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