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I am an amateur hobby electronics enthusiast , and given the situation , I too am trying to make a contactless hand Sanitizing system like everyone else. My project requires a 36V DC solenoid valve to be actuated through the arduino momentarily for the sanitizer to drop. Obviously I will be using a relay module to electrically isolate both the circuits. But I don't have a 36 V DC adapter . So what is the best way to power up the solenoid valve? Batteries are available to me right now? How do I calculate how many 9v batteries do I need ? How many AH would they require ? Would they get drained too fast?

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    36/9 = 4. AH defines the amount of time they will last at a certain current draw. You need to know the current draw and how long the solenoid will be powered for. – Majenko Jul 13 '20 at 13:20
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    If you’re talking about the square looking 9V batteries then save yourself some money and don’t even buy them. They’re not appropriate for driving motors. They can’t produce the current you need. Get AA batteries for this. You need enough to make 36V. It will be a lot. You’d be better off getting a LiPO pack or just using a smaller servo. – Delta_G Jul 13 '20 at 13:31
  • My HP printers had 32V adapters, which will probably work too. Maybe you can salvage one from an old printer gathering dust somewhere in your house. – Gerben Jul 13 '20 at 18:08
  • two old 18v ungrounded laptop supplies could be put in series to get 36v; those are safe and dirt-cheap. – dandavis Jul 13 '20 at 19:16
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    For the record, 36V is hardly a "high voltage" DC device. The term high voltage usually implies something well over mains voltage. It makes me think of thousands, or even tens of thousands, of volts – Duncan C Jul 13 '20 at 21:23
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Batteries are going to be annoying because they're run out and have to be recharged/replaced. A mains power supply would be easier to "set and forget.

I did a google search on "36V DC power supply" and found a 4A power supply from "Alitove" on Amazon for $22.99 US. That should be fine. (Assuming you are somewhere with 120VAC mains power. If you live somewhere with 240VAC mains power you would need a different unit, but since I found one, I would expect a google search in your region would find one for your area.)

I would suggest using a logic-level MOSFET transistor + flyback diode to switch your DC power. That's easier to do than a relay (That would require another power supply.)

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