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Need some help powering motion detector water spray


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Hi there, hope someone can help.

Ok firstly i am trying to build a water spray system that uses a 12v Solenoid which will be controlled by a PIR module. Here are the parts i have so far;

12v Solenoid: DC 12V 1/2″ Magnetic Electric Solenoid Valve for Water Air Normally Closed | eBay
PIR Module: PIR IR Pyroelectric Infrared Module Adjust Relay Output Human Body Sensor 12V XD | eBay
Rectifier Diode: 4 off 6A6 Rectifier Diode 6A 6AMP 600V RoHS | eBay
+Various housing parts and connections for the hose pipe

It is to stop next door neighbours cat from cr@pping on the driveway. So when the module detects motion it will open the solenoid and water will shoot out.

I have basically been following a guide on YT, but on the video he is using a 12v power adapter plug, whereas I want to use rechargeable lithium batteries.

Any advice on the batteries? Which ones i should use, and also the wiring of the battery pack?

Many thanks, im a novice when it comes to this sort of thing hence following the guide on YT, so any help or advice would be great 

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You could use three 3.7v cells to make up a 11.1/12v battery. For example  three 9800 mAh would be; 9.8 Ah * 11.1 or 108.78 Watt hours. The valve only use 4.8 watts and the standby current for the IR unit is only 50 microAmps. For example:


Finding a charger that charges an odd number of cells is a challenge. There are slot chargers that charge cells in parallel that would be helpful if you can find one.

The 11.1 batteries as used for radio control airplanes are expense and require balanced chargers.

My IR animal detector uses a standard 9v battery that lasts for many weeks.

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Awesome thanks for the help. I have got 3 Samsung 18650 batteries, so was planning to use those, although they are 3.6v so my output would be 10.8v - Do you think that would be ok?

I have purchased this 3 cell battery holder 18650 Battery Holder Storage Box Case 1 2 3 4 Cell 18650 DIY Soldering | eBay 

And also this BMS board 3S 10A Balance Li-ion Lithium LiPo 18650 Battery BMS Protection PCB Board 12.6V | eBay


As i already have a separate charger for the batteries, the circuit doesn't need to accept charging, (i plan to remove batteries and recharge when needed),  but do i still need the BMS board, if I'm charging batteries separately? From my understanding the board helps maintain the discharge rate of certain cells so they don't go too low

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Your cells should charge up to 4v or so; I would think them to be okay.

The BMS board is for charging. There are cells with protection built-in but they are expensive.

There are simple devices you may add to a cell for such protection: Here is a video on single cell protection: https://www.youtube.com/watch?v=oIE6bWj-lSU

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