Okay, I had a previous post with a question about running an AC aquarium pump. I built a relay circuit with a mechanical relay, but now want to use an SSR so there is no clicking noise when the relay switches on. I'm in the U.S. and will be switching 120v AC. I will be using a Crydom AS0241R. Here is an address of the datasheet
So, from what I understand, I do NOT need a diode since it is not a mechanical relay.
The typical input current is 15mA and the nominal input impedance is 300 ohm for this SSR.
If a circuit is needed at all, I've worked out that if I use a 2n2222 transistor, I should use a 12k ohm resistor. (Using the information at Transistor Circuits) Does this sound correct?
Since the input current is only 15mA, and the arduino is (I think) 20mA can I hook up the SSR directly to the arduino? If not, what is the deciding factor that allows an SSR to hook up directly?
I've really appreciated past help and can usually find my questions answered in this forum, Thanks in advance for any help you can give me.
I've fried my first SSR that way. You need current limiting resistor, I think.
You would have to show me the datasheet for the specific SSR you were using. All the ones I've ever seen specify a DC voltage input to turn on the device and no current limiting resistor required. A common input voltage spec is 3-12vdc. OP's spec sheet showed 4-10vdc control. The current limiting resistor is built inside.
Thanks to both of you. Looking again at the data sheet, does the "insulation resistance" count as the resistor? How can I tell that it is built in? Also, do I not need a transistor because of the 15mA input current? I'm just trying to understand this as fully as I can. Thanks for your patience with me!
"insulation resistance" count as the resistor?" No that is a safety specification, you don't want the 120vac arcing over to the control pins, so the combination of internal optical isolation and the insolation the package material make up that specification.
"How can I tell that it is built in? " Because the spec sheet says if you supply 5vdc to the control pins it draws 15ma. R=E/I so internal current limiting resistor is 333 ohms.
Also, do I not need a transistor because of the 15mA input current?
Yes, an Arduino output pin has a max current spec of 40ma, running them at 20ma or lower is best, 15ma is just fine, no transistor required for that low of a current.
Yep, that one will burn out the internal LED without using an external current limiting resistor. That is not typical on most SSR, but as you found out there are always exceptions to the rule.
