Can anyone please recommend power supply to go with * Raspberry Pi 8-Channel Relay Board
This video may help: Raspberry Pi: 8 Channel Relay + External Power Supply Tutorial and Example - YouTube
Hi Manish,
Welcome to the forum 
The Raspberry Pi 8-Channel Relay Board has a 5V terminal block you can use to connect power to it, but you should also be fine to power it via the Raspberry Pi as long as the power supply you use with your Pi is decent.
I had a quick look through the schematic for the relay module and it looks like the 5V terminal block and Raspberry Pi 5V GPIO pin are connected together on the circuit board, so be mindful of how many devices are connected to the Raspberry Pi and relay module. I think the Raspberry Pi official power supply should have enough headroom for both the Pi and the relay module.
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Hi Trent
Be a bit careful here. I just had a quick look and as usual could not find any details about what relays are fitted to this device. You are implying that the RPi supply could power both the RPi AND the relay board. The Optocouplers yes but the coils are a different matter. The Omron relays used in the Pololu 2 relay module require almost 80mA per relay coil. As I say I don’t know exactly what relays are used in his board so measure the DC resistance and work it out. I think Omron would be as frugal on current as any and even on this basis you are looking at 640mA with all relays activated.
Anyway after all this I personally would not use the RPi power and would be looking at a separate supply for the relay power. My opinion.
Cheers Bob
PS. Just had a look at the schematic you linked and you are right, the 5V does seem to be connected to the RPi 5V. This could limit a whole RPi to just driving this relay board. I don’t think there would be much left over for anything else. Option would be to use another 8 relay board and a separate supply or modify this board. Best of luck.
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Hi Bob,
Often Raspberry Pi HATs and add-ons will have some sort of a removable link so that the external power supply can be isolated from the power supply to the Pi itself, this doesn’t appear to be the case for this relay module. I think one appropriately sized power supply would generally be better than trying to feed two separate supplies into the same power rail.
The reason I recommend the Official Pi power supplies is because they have designed them with headroom in mind. The power supplies will deliver 5.1V@3A without any USB power negotiation involved.
The Pi’s documentation allows up to 1.2A of current for peripheral USB devices and recommends a 3A power supply when the Raspberry Pi unit alone at full CPU load will peak at 1.25A draw.
The end user obviously has to be sensible and not also connect everything under the sun but as you pointed out the 8 relays themself ought to be under an Amp combined.
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