ESP8266 Community Forum

Just a warning about the Fotek SSR-25 DA solid state relays that are widely available (and cheap) on EBay. Unfortunately, the 3.3V put out by the ESP8266 GPIOs isn't enough to get these relays to close. Apparently, they close at about 4.5V, despite the labelling saying 3V. My Internet controlled relay project was just stopped in its tracks because of this erroneous labelling.

Apparently, the Fotek SSRs can be modified to work by bypassing a resistor on the positive control input, but I haven't attempted that yet.

A work around with an opto-isolator, a transistor, and a couple of resistors is easy enough to implement as long as one has 5V or greater power available.

Even so, an endorsement of an alternative solid state relay that works reliably at 3.3V and is similar in price to the Foteks on EBay (~$3.50 US) would be welcome. There are Omron based modules (ie. this one) that look like they might work.

If its a real OMRON and they say its 3.3V, then it is, OMRON is a very reputable company.

Richard.

There are some SSR modules on EBay that seem to employ OMRON relays. Point taken on whether they are real OMRON relays or not. Looking closely at the pictures, they are labelled as 5V. However, the specs (provided by the EBay sellers) state that they close at 2.5-5V and open at 0-1.5V. The safest interpretation of which would be that they aren't guaranteed to close with a control signal of less than 5V and open at more than 0V. And these can only handle 2A. Still, at a couple of dollars, they are probably worth a try.

In my case, I just used a logic-level MOSFET (a Fairchild 76137P that was laying around) to control 5V from my MB102 power supply. Using a MOSFET is fine for a proof-of-concept (and to impress my boys for about four seconds), but having 5V available might not be without pain in certain applications.

RichardS wrote:If its a real OMRON and they say its 3.3V, then it is, OMRON is a very reputable company.

Richard.

According to datasheet http://www.mouser.com/ds/2/307/g3mb_0609-298620.pdf, you will need at least 4V to make them effectively turned ON, except with model without internal resistance G3MB-202PEG, but it was not the one on your picture link.
So, you still need higher voltage on anode and drive it with MOSFET or ULN2803.