I have a solenoid which I pulled out of a machine that I have lying around and have a solid state relay. I plan to connect digital out from Uno to Relay to Solenoid.
I need advise on the following please:
Size of diode that is connected to the solenoid (or whether I will need one since I am using a solid state relay) ?
Whether the solid state relay size and specs I have will work for this solenoid?
I could not find a spec sheet of the solenoid but have attached a picture of it below. The specs listed in the picture are:
220V - 50Hz - 5.7VA 220V - 60Hz - 4.6VA
We use 50Hz in the country I live.
The digital relay I have specs are:
Omron G3MB-202P, to control current upto 2A@240VAC Control Voltage: 5V Static Current: 0mA Working Current: 12.5mA Trigger Voltage：0-1.5V Trigger Current：2mA
A DC operated electro-mechanical relay should include a diode across the coil. The current through the diode is equal to the current through the coil for an instant after power to the coil is removed.
Solid state relays don't have a coil so you don't need a diode on the input-control side.
Just to confirm, the solenoid is 220V - 5.7 VA. I googled around and found a formula to calculate what the amps requirement (VA to A), my calculation is approx 0,27 A.
So as the relay is rated at 2A, this should be a suitable relay?
First VA = Volts * Amps. So for your valve: the current in Amps = VA/ Volts = 5.7 /220 = 0.026 amps.
I looked up the Omron G3MB-202P and found the load current to be 0.1 A to 2 A
Your valve is well below the max current but also below the min current (0.1A). A characteristic of AC SSR is the output device (Triac or parallel SCR's) needs some amount of current to stay on after the initial trigger by the internal circuitry. Your load may not be enough to keep the output on. The output device parameter that specifies this is called the "minimum holding current"
I suggest you try it out and see what happens. Measure the ON voltage across the valve. If it is at or near you line voltage you are OK. If not, add an incandescent lamp in parallel with the valve and see if the ON voltage changes. If it does the valve current is too low for the SSR.
Inductive loads like a solenoid require you to check the inductive load ratings of the relay and maybe select
a snubber network to reduce arcing. Fortunately that OMRON relay has snubber built in, but note the
current rating is less for "motor" loads, which means inductive load.
You can add a suitable mains-rated load resistor if the minimum current is an issue, just check the
power rating and ensure it is fully insulated. An extra resistor across the solenoid will also help
with snubbing.
Thank you for the reply and knowledge sharing. I did not know to consider things like this! I only look at maximum. Will connect the circuit tomorrow and hopefully it will work without needing the lamp. Worse case scenario, I can purchase a relay with a lower minimum
JohnRob:
Your valve is well below the max current but also below the min current (0.1A). A characteristic of AC SSR is the output device (Triac or parallel SCR's) needs some amount of current to stay on after the initial trigger by the internal circuitry. Your load may not be enough to keep the output on. The output device parameter that specifies this is called the "minimum holding current"
Thank you MarkT. I had to scroll through the datasheet a few times to see how you picked up the "motor" loads
Will do a test and also have read now more about snubber circuits and how they are used and how to calculate.
Thank you!
MarkT:
Inductive loads like a solenoid require you to check the inductive load ratings of the relay and maybe select
a snubber network to reduce arcing. Fortunately that OMRON relay has snubber built in, but note the
current rating is less for "motor" loads, which means inductive load.
You can add a suitable mains-rated load resistor if the minimum current is an issue, just check the
power rating and ensure it is fully insulated. An extra resistor across the solenoid will also help
with snubbing.
