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
You are going about this backwards, I think. You need to start by telling us what the relays are controlling (voltage and amperage).
Individual relays may be a better choice than a relay board, especially if you need to control so many of them.
Power consumption, ease of access, heat dissipation, etc. are all factors to be considered.
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.
BASICS:
the RELAY as a separate device, requires power. you can get relays that are less than 5v, are 5v, 12v, AC, DC or whatever
the relay is mounted on a board with other parts to make a device.
the power you feed the board is SEPARATE from the SIGNAL you send. NEVER FEED A RELAY POWER FROM THE ARDUINO BOARD.
on relay boards that have the signal to a board with a different voltage than the relay, the opto is a very good way to separate the two power supplies and DO NOT require a common ground.
for a relay board that does have a 5v power and your output is 5v AND you want to use transistors, you must tie the grounds together. The vast majority of cheap relay boards use opto's because the application is nearly universal. the market for 5v relays with transistors is nearly insignificant.
the opto allows complete separation of power sources.
the basic operation of the opto is exactly the same as and LED. all you need to do is to light the LED inside of the opto.
POWER SUPPLIES :
with relays, I like having a separation of power supplies. it removes one possible problem with noise.
second, your relays will consume power . if you have a raw, dirty 5v, the relay will be happy. the Arduino ? not so much.
if you have 12V, and you need to drop that to 5 for the arduino AND the relays, you need a larger voltage regulator. AND it has to be separate and filtered from the arduino.... or, just use that raw 12v to power the relays.
Thanks for the replys
Im only going to use the relays to control solid state relays that are located around the house mounted in electrical outlets so that should not be a problem. I have alot of 12 volt relays kicking around is there any way to make my own relay board using SCR's Silicone controled Rectifier