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I have 6 5V solenoids connected to an Arduino Uno, each of them with a TIP120 transistor, diode and resistor. Exactly like https://core-electronics.com.au/tutorials/solenoid-control-with-arduino.html but 6 times. I'm using a 9V battery connected to the DC input, as well as USB input to my PC.

Now the problem is that if I activate 5 or 6 solenoids at once, the Arduino seems to get interrupted / lose all power for a second (disconnect sound from the PC and no activity). I've tested them one by one and everything works, but I can activate at most 4 solenoids at once.

What am I missing? Do I need more power?

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I'm using a 9V battery connected to the DC input

Well, there's your problem. Those 9V PP3 batteries are barely enough to power the Arduino by itself. Add anything like motors and solenoids and you're going to have problems. Big problems.

Ditch the PP3 battery. It's only suitable for very low current devices, like smoke alarms. For anything more you need at least multiple series AA batteries.

Also the solenoids must be powered direct from your power source (or through their own regulator if needed), since the Arduino's on-board regulator will go into thermal shutdown quite quickly with 9V in and a large current draw.

  • I should've mentioned I've also tried a 6x AA battery pack on DC, it gave the same results. And I'm not sure how I can connect them directly to my power source? – SJ19 Mar 25 at 7:46
  • @SJ19 Take the wire out of the 5V pin on the Arduino and connect it to your battery + (assuming the battery isn't too high a voltage for your solenoid). – Majenko Mar 25 at 10:25
  • Thank you! Guess I should be looking for a battery connector with wires then. Excuse my ignorance but do you reckon a 9V battery will be too much for the 5V solenoids? – SJ19 Mar 25 at 10:54
  • @SJ19 If they are actually 5V solenoids, then yes probably. You will want a 5V regulator. Get a UBEC from an RC model seller - they're the simplest option. – Majenko Mar 25 at 10:55
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Another possibility is to use latching solenoids controlled by an H-bridge so that they only need power to turn on or turn off. However, I don't know if they are available for your application. When I looked into latching irrigation valves they were much more expensive than simple solenoid valves.

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You're experiencing a lack of available current. When the solenoids are operating, the system is trying to draw more current than the battery can provide, so what happens instead is the voltage starts to drop. (I can't remember exactly why this happens right now). When this happens the arduinos power supply detects an under-voltage condition and shuts down, but as soon as it shuts down the current draw tanks and the voltage rises again causing the system to restart. Essentially, the answer to this is to provide your system with a larger current source and the problem should go away.

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