Trickyrick:
Hi guys
Looking for a relay board for my Arduino preferably 16 channel. I have read that some prefer the sainsmart relay boards as they have optoisolators. I have being on SainSmarts web site and in the description some are 12volt and some are 5 volt. Does it matter, is that referring to the optional power supply to control the relay board. As Im new Im thinking that the signal voltage from the Arduino is 5 volts and that this has nothing to do with the voltage in the description on SainSmarts web site ?
Thanks
Most of those Asian relay boards do have opto-isolator inputs (but a few do not), however to take advantage of total galvanic isolation the relay coil power and ground must be independent of the arduino 5V and ground pin. So if you wish total isolation you need an independent external DC power supply with a voltage that matches the relay coil requirements and enough or more current capability to handle all relay coils being activated at the same time.
But PaulS is correct in that the relay contact ratings are the first requirement you have to select before what the 'secondary' requirements are for the relay or relay board.