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Description: A solid state relay (SSR) is just what it sounds like; an IC that acts like a mechanical relay. They allow you to control high-voltage AC loads from lower voltage DC control circuitry. Solid state relays, have several advantages over mechanical relays. One such advantage is that they can be switched by a much lower voltage and at a much lower current than most mechanical relays. Also, because there’s no moving contacts, solid state relays can be switched much faster and for much longer periods without wearing out.
They accomplish this by using infrared light as the ‘contact,’ a solid-state relay is really just an IR LED and a phototriac sealed up into a little box. Thanks to the fact that the two sides of the relay are photo-coupled, you can rely on the same type of electrical isolation as in mechanical relays. These particular solid state relays can switch 400VAC and 8A.
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2 of 2 found this helpful:
It is very easy to integrate this into a project since Sparkfun provides the EAGLE footprint and sample circuits. I was able to add an AC switching element to my board very quickly. Initially, I was wondering why it was AC only and then I realized that when you switch off the relay, it is only changed once the load passes through zero volts and goes negative. As a DC load does no such thing, this device can switch it on - but not off.
The device is functions as expected and it is clearly marked for AC loads by Sparkfun so this is just me pointing to the obvious.
1 of 1 found this helpful:
Used this in my very first Arduino project and was quite satisfied. Using it to switch 150 watt resistive load - rather tame for the 8 amp rating so there is no heating issue.
This is the smallest sold state relay I found and it is very nice and easy to install..
This relay is a huge upgrade over the mechanical relays you might be used to (no clicking, much more reliable). However, keep in mind a few things..
1) The internal switching mechanism is an IR LED, so don’t forget a current-limiting resistor in your design! (I’m glad I bought two, because I fried my first one.. facepalm.)
2) While the current rating is 8A, you’ll need a heatsink to operate this high. Without a heat sink, you shouldn’t operate at >2.5A at room temperature. Be sure to check out the datasheet (p.6 Fig.2) for more info.
I’m using a tiny arduino to turn a street light on and off using a Cadmium Sulfide Cell. I’m using this relay to switch the 120v power to the mercury vapor street light. When the light comes on it pulls several amps as the arc starts, then the current demand decreases to about 1.5 amps. This switch has worked perfectly for two weeks. I just purchased 3 more just to hold in case I have another use for them. It cycles on/off once a day and stays on for about 10 hours.