I'm making a simple watering system that operates a solenoid valve via a 5v relay connected to a 12v battery. 1. Do I need a flyback diode on the solenoid? I'm guessing that the relay will protect the Arduino from flyback and noise, but it wouldn't hurt to add a diode to protect the relay. Solenoi…

Always use a free-wheel diode with an inductive load in a DC circuit. The relay contacts will arc loads if you don't and may be rapidly destroyed or weld shut.\ Run separate wires from the battery to the relay and to the Arduino supply, ie use a star- ground arrangement for minimal interaction / …

Here is a 4 relay PCB illustrating the jumper. However, as Mark said the relay supplies isolation. Unless you have a second 5v PS, leave the jumper. .

Thanks for the quick replies. I'll definitely put in a diode. Just to clarify, in this situtaion the diode is there to protect the relay, not the Arduino right? What is the correct value diode to use? MarkT: Run separate wires from the battery to the relay and to the Arduino supply, ie use a st…

The diode protects the contacts and keeps noise spikes from causing problems with the Arduino. Use separate (star) power leads to keep devices from interfering with each other. Necessary if you want things to work. .

LarryD: Use separate (star) power leads to keep devices from interfering with each other. Necessary if you want things to work. I'm getting more confused. So instead of getting the 5v for the relay from Arduino (as in the pic), I have to get 5v for the relay from the battery? Or are you just …

Xerosene: I'm getting more confused. So instead of getting the 5v for the relay from Arduino (as in the pic), I have to get 5v for the relay from the battery? Or are you just talking about keeping the 12v that runs through the relay separate? I've got a fuse sitting on the bench :wink: I just …

I didn't notice that you'd moved the 5v lines to the buck converter ... makes more sense now! I think all my build questions are answered now. Thanks. I'll hook it up tonight and see what happens. Link to relay is in first post. Not a heap of info there... http://www.chinalctech.com/index.php?_m…

One last thing... Do I put the fuse on the 12v into the relay, or (most likely) right back at the battery before the buck converter as well? OR

Put the fuse on the battery lead - its there to prevent wiring catching fire, not really to protect your electronics(!) The opto-isolation thing is available on most relay drivers, you don't have to use it, so don't worry about it.

Flyback diode required for relay board and 12v solenoid?

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LarryD December 5, 2016, 12:18am 6

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Flyback diode required for relay board and 12v solenoid?

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