
I bought a couple of these modules after they were burned by one of the cheap relay modules you can buy for 1/2-1/4 the price. This board is a step ahead of the rest in almost every way + Detachable connectors. If you plan on using 14 gauge wire to power high voltage relays, the convenience of these connectors already makes this board a good choice. Even if you have a high utilization application, the removable pin headers make it much easier to replace a new board when the relay finally fails. + High quality connections. Very strong and they snap very tight. Unlike the connectors on my cheap relay module, which even break if you look at them the wrong way. + Large plugs. The connectors are large enough to accept two 14 gauge cables, making it much easier to connect to common inputs.+ Did I mention connectors?+ Genuine parts? I can't verify this, but the paint on the SONGLE relay is lighter and crisper than the cheap relay module. + Robust circuit board. The thickness is about 1.6mm compared to 1mm for a cheap relay module. It is very convenient to tighten these strong headers. + Heavy. The 4 channel module I bought weighs about the same as a cheap 8 channel module. + The ability to extend the module is a nice trick, but I doubt I'll use it. + documentation. The wiki page is great, SunFounder has done everything here. + Air gap between high voltage and low voltage side. They took the time to route a piece of circuit board between the high and low voltage sides. + Power LED in addition to relay status LEDs. The cheap relay module had good status LEDs but no power LED. Nice gesture. Now for the cons: - terminal labels for screen printing are below. This means that once the card has been installed, you will no longer be able to read the connector labels. In fact, I just noticed that the values are printed at the top but hidden by removable headers. - Small traces of high voltage. A cheap relay module has much wider high voltage traces. I'm hoping the SunFounder board actually has deeper traces and therefore the same or greater cross-sectional volume, but I'm not going to cut my board in half to find out. The air gap is much smaller than a cheap relay module and does not fully isolate the common input from the enable terminals.

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