Help for checking relay circuit

[Jeff27]

Hi Guys,

Can you please help me check my relay circuit, I am using Arduino to control a 230Vac solenoid valve. When I press the mini-push button, the solenoid valve will be turned on.

I see people often use an external 12V power to control the relay, but can I use Arduino’s built in 5V power to control the relay directly like my drawing ? The solid state relay I am going to buy (people recommend solid state to me) is also shown below. Can you notice any problem with the circuit ?

I want you guys say it’s OK because I don’t want to burn my Arduino or commit suicide at home …

Thank you very much.

Regards, Jeff

[Jeff27]

Sorry guys, I think the rectifier connected to the solenoid is wrong, I guess this should be right now…

Also, can I ask how to choose relay output ? Whether it’s 25A or 30A or higher ?

My solenoid valve does not say the working current, only given the inrush power consumption of 100 - 120 (VA), and 32 at holding position. Based on your experience, for a 230Vac valve, would an output of 25A be enough ?

[Jeff27]

JohnLincoln:
This is a typical snubber circuit, consisting of 0.1?F in series with 100? :
http://uk.farnell.com/ampohm-wound-products/fe-sp-cr23-100-100/contact-suppressor-0-1uf-100r/dp/1438322

Hi John, thank you very much for your reply. So, basically, my previous diode setup is for DC powered devices, right ? That’s why it will not work for AC powered circuit, I didn’t realize I made a big mistake before that. And can I ask that, is that only because I will have an inductive solenoid in the circuit, so I must have the snubber circuit for prevention of fly back voltage spike, right ? Because I don’t see people use it for bulb circuit with 230 Vac mains.

So, the snubber circuit will be connected in parallel to the solenoid ? Or before the load and between the hot and neutral power line like the drawing below ? I wonder if the snubber circuit is now a standard built-in part in the relay, so I only need to connect my load with the relay ?

Regarding to the relay, do you mean for a solid state relay which is not inductive , I don’t need a diode comparing to the electromagnetic relay which is inductive ? Although solid state relay has a longer life span, whats the benefit of the electromagnetic relay ?

The CONTACT SUPPRESSOR you suggested is rated for 250Vac, I noticed there are many AMPOHM suppressors with different rating, for example, 0.1Uf 47R or 0.22Uf 100R. How to select the right one for me, for example, my solenoid valve runs at 230V. Is that the larger the Uf and resistor, the safer I will be ?

And can I use Arduino’s 5V power to drive the relay if the relay has a rating from 3-32V DC ? Because I see many people tend to use an external 12V power to control the relay.

I watched a video, saying something about the Zero-crossing detector in circuit. I guess the zero-crossing detector is now a standard built-in part in the solid state relay so that I only need the relay ? Guess also true for the snubber circuit, also comes like a built-in part in the relay ?

Although you have shown your circuit built on a solder-less breadboard, this is totally unsuitable for use with mains voltages.

Thank you for the tip, although there are many videos on Youtube showing 230V bulb circuit on solder-less breadboard.

[MarkT]

Snubbers, or freewheel diodes in a DC circuit, always go across the inductor
that would otherwise generate high voltages. Think about it, its the only place that
such protection can go and have an effect...

Snubbers should be roughly matched to the load current and inductor, and also they
dissipate some power so the resistor needs sizing correctly. They also don't prevent
inductive spikes, merely limit the voltage from many kV to something less extreme.

[Paul_B]

While I suspect you did not really mean this, your graphic suggests the SSR is plugged into the breadboard, but since vertical columns are each a single connection, that would be shorted out on both input and output.

You also show the pushbutton connected to V_cc (5V) with a pull-down resistor. Whilst this is regrettably what is illustrated in many or most Arduino site tutorials, it is very poor engineering practice. You should connect the pushbutton to ground and set that pin as INPUT_PULLUP to utilise the internal pullup.

You do not (generally) need a transistor to drive either a SSR or an optocoupler as these will generally trip below 20 mA; you just need to figure the series resistor to suit. Note that you do not attempt to measure milliamps in series with such a resistor; you measure the voltage across the resistor during a trial, and calculate the current knowing its resistance.