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Topic: Arduino freezes whenever relay has 120v current passing through  (Read 403 times) previous topic - next topic



I checked the manufacturer's website and didn't find anything about a snubber circuit. I included a picture of the connection to the solenoid valve.
Be aware that a datasheet is designed to describe the features of the particular device, not to teach
principles of electronics, as the reader of the datasheet is assumed to understand these.

A solenoid, motor, relay coil, these are all inductive loads that require attention to prevent inductive
kick-back.  For DC a free-wheel diode is often the simplest approach, for AC an RC snubber is typically

And datasheet quality varies anyway.  The solenoid valve datasheet may have been written by
a pneumatics engineering team, not an electronics expert, since its a pneumatics component.

Another example: there are many datasheets for logic chips that don't explicitly state that decoupling
capacitors are mandatory, but they are, you are expected to know this.
[ I DO NOT respond to personal messages, I WILL delete them unread, use the forum please ]


Wawa thank you for the detailed description of how to fix the project. I will make then changes and come back with an update. Your help is greatly appreciated!

JCA34F, I stated 9v by accident because I use to use a 9-volt battery for that port, how I am using a 5-volt power supply for it.

MarkT, I will keep this in mind next time I look at a components date sheet. And thank you for the specified RC Snubber circuit.


I use to use a 9-volt battery for that port, how I am using a 5-volt power supply for it.
Did you mean 'now'.
Can't do that.
The DC socket of a breadboard supply needs at least 6volt for it's regulator to make a stable 5volt.

Don't know your modding skills, but an old cellphone supply (thrift store) with USB lead, that you can cut off the plug, is an excellent 5volt supply that can power that relay board directly.
The rest of the project should be powered from the Arduino.


Yes, my apologies, I am using an ac/dc adapter which can vary its output from 1.5v-12v, I had it set to 5 volts and I have now changed it to 6v.

I have taken a look at a bunch of ways to use snubbers, all of the snubber boards that I have found however on eBay and other sites can only come in late October to November. Are snubbers things you can only buy or can you make one with the components? I have seen people use a diode across the relay switch and other things such as a capacitor and resistor across the switch. Would a single diode work, or would I have to make a more intricate system.

Thanks a ton!


Snubber circuits (a capacitor and a resistor in series) are used in (almost) all home appliances with motors, like vacuum cleaners. Can't you go to a local repair shop?

Diodes are for DC, not for AC (mains) circuits.


Thanks for the clarification, I'll be sure to stop by a repair shop soon.

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