So after burning up a couple Arduinos, I'm running out of ideas...

I am trying to power both a Solenoid valve and the Arduino(nano) with the same 12V-2amp power supply. I've tried it with both a relay breakout board, and via transistor switching, and both are giving me sporadic behavior for the Solenoid.

Early failures came from realizing that the solenoid water value was actually a coil (duh), and thus needed some kind of diode placed over its connections, so I'm assuming the back voltage spike is what fried the first two boards.

At first I added a small diode that helped but wasn't enough, so I beefed it up to a 3 amp "rectifier diode" 200PIV, which stopped the board frying.

Here is a link to the solenoid water valve. Not much to go on I'm afraid. 12V 0.02-0.8Mpa.

The behavior that I'm seeing now, is that the solenoid will engage, but it won't disengage.

Do I need to add a Capacitor for the solenoid? If so, any recommendations on sizing?

Fritzing Schematic

int relayPin = 2;

void setup() 
  pinMode(relayPin, OUTPUT);

void loop() 
  digitalWrite(relayPin, HIGH);
  digitalWrite(relayPin, LOW);
  • The valve might require the water to be pressurized, to disengage properly. Using the water pressure instead of a sprint, like in regular solenoids.
    – Gerben
    Apr 6, 2016 at 18:22
  • Sorry, I did leave out that it's a "normally closed" solenoid. I've tried direct powering with the 12v supply and it works fine that way.
    – ZacWolf
    Apr 6, 2016 at 21:37
  • Please double check your transistor pinout. The TIP3055 you name doesn't come in the TO-92 case you depict.
    – sekdiy
    Apr 9, 2016 at 23:00
  • The red wire is connected to the Arduino or the power supply? Not very clear in the picture.
    – user31481
    Jul 7, 2017 at 22:30
  • It's a prototyping board, so each vertical line (when laid horizontally) are all connected. So you'll see the the 12v power is provided to both the arduino and the solinoid
    – ZacWolf
    Aug 5, 2018 at 15:01

3 Answers 3


I have setup Arduino UNO and succeeded turning solenoid on when pot soil moisture dry, I was adding rain sensor when I mistakenly disvmcoonected the diode it fried my board, but atleast I had it working . I am using 24 volt normally closed solenoid , since I was monitoring over web I also had ethernet shield attached. And I was powering over ethernet using splitter and extracter.

enter image description here

The vin should only feed in 3.3 volt which you can get using stepdown buck converter , and use remains power to connect to solenoid. The transistor should be on the ground same as arduino nano the ground The top became messy later enter image description here

  • What I've discovered is that the step-down is the key. Because using the same 12v ground for both the arduino (directly) and the solenoid creates a feedback loop of some kind that keeps the transistor energized. The step-down buck your using to provide power to the arduino at 3.4V must include some kind of diode that is keeping the voltage from flowing backwards.
    – ZacWolf
    Feb 6, 2019 at 16:34

enter image description here

Try This Circuit...

  1. I think you are overpowering Arduino Board.

  2. Transistor Will not Carry heavy current for long duty period.

  3. It easy to use Simple 5v relay board then you don't have to worry about Current limits and all...

  • 1
    If you review my diagram this is the exactly same setup I had already outlined, just using a different transistor. I'll try again with a TIP120.
    – ZacWolf
    Aug 5, 2018 at 15:04

The fact that the solenoid turns on but not off makes me think the Arduino might just not switch off the GPIO. This could happen if the current drawn by the solenoid is so high that the power supply voltage drops below the threshold needed for the Arduino, resulting in a reset.

The result would be that the Arduino repeatedly switches on the solenoid but is reset before it can switch it off again.

Try to flash the built in LED in the same main loop to verify that the loop is still alive.

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