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Ohio
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Hello,
I have some of these SSRs, http://www.mouser.com/Search/ProductDetail.aspx?qs=8ehJfnwBfpTEixK6L1K8TA%3D%3D.
Looking at the datasheet here, http://www.crydom.com/en/Products/Catalog/s_1.pdf I have a few questions.

What does "Zero-crossing (resistive loads) or random-fire (inductive loads) output" mean?

And it says, "Typical Input Current 3.4-20 mA" and "Nominal Input Impedance [Ohms] 1500 Ohm". Does this mean I could omit a current limiting resistor as the internal impedance would limit it to 3.3mA (5v/1500Ω=3.3mA)?

I have also been reading that a snubber is not needed for SSRs. Will someone confirm or give argument otherwise?

Finally, is something like this safe to control directly from an output pin or should I use a transistor to switch it?

Thanks for your time,
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Does this mean I could omit a current limiting resistor as the internal impedance would limit it to 3.3mA (5v/1500Ω=3.3mA)?
Correct.  If you want to be extra-safe*, you can use one and still get enough current/voltage to trigger the SSR.

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What does "Zero-crossing (resistive loads) or random-fire (inductive loads) output" mean?
The zero-crossing version switches-on shortly after the AC power crosses-through zero.   I think the advantage is that you don't get noise on the AC line if you switch at zero.    SCRs and TRIACS always turn off at the zero-crossing.  (It won't work as a dimmer, which needs to switch-on at different points/angles depending, on the dimmer setting.) 

I'm not 100% sure why the non-zero crossing version is needed for inductive loads... so I'd better not guess.

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I have also been reading that a snubber is not needed for SSRs. Will someone confirm or give argument otherwise?
On the input side?   That's right.  There is no inductive coil with a solid-state relay.

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Finally, is something like this safe to control directly from an output pin or should I use a transistor to switch it?
With the low voltage & curent requirements, you can drive it directly.

* Let's say you've got your low-voltage contorller in one box and your high-voltage and SSR in another box with connectors & cables running in-between.     If there's a limiting resistor inside your low-voltage box, the Arduino won't get killed if someone shorts-out the outputs.
« Last Edit: February 15, 2012, 07:31:38 pm by DVDdoug » Logged

Ohio
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Thank you, these were the answers I was hoping for. My son and I want to make some simple ir remote controlled lights in the house so knowing these will work is good, knowing that I don't have to spend any money is great!
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The snubber (a series R-C) would be protecting the SSR output circuit when/if connected to an inductive load.  Some come that way, some don't, I don't think that's "a given".  As you're just doing lights, the point is moot, because they're resistive.
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Ohio
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Looking at the datasheet for this particular relay, a snubber is included, so even for inductive loads nothing else would be required, correct? (see attached) And since it is optically coupled, there is no need to have anything on the low-voltage side? Please tell me this is right and my understanding of them isn't completely wrong.


* ScreenShot001.bmp (2058.91 KB, 1348x391 - viewed 91 times.)
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You're covered.
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I have been running one of these to turn my spindle on and off for my CNC Router. I have been running it for 4 years with no issue. Control voltage (5V) on input and 120 AC on the output. Straight forward connection.

Just thought I'd give you some real world assurance. Also, check e-bay. Depending on where you live, you can get them much cheaper.

WB-
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Ohio
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Reassurance is always nice. As for the price, I've been throwing these away for years. I work as a tech at a medical equipment manufacturer. We only do board level repair but since I've started tinkering I've been more observant of what is discarded as scrap. LEDs, 20x2 and 20x4 LCDs, small and large relays, PIC16s by the handfull (tried to start with these but found the Arduino community much larger), etc.., I could hardly contain myself when I realized we use the MAX7219 as the 7 segment drivers. But anyways, I'm just rambling now...
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But anyways, I'm just rambling now...

That's why I come to this forum! Rambling nerd shit is good! My wife doesn't understand.

I forgot the question , now.

WB-
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