Wawa:
The relay coils pull about 80mA each from the power supply when active, but the Arduino pin signal current is only 2mA.
Both relay module and the Nano could be powered with a 5volt/1Amp cellphone charger.
Don't power the relay module via the USB connector of the Nano.
Leo..
Wowa, yes it's about 85mA so almost 0.7A for the 8 relays. I also have an RS232 and the Arduino itself. And whatever I use for the amps will have some loss. So I plan to use a 5V/1A power supply wired to pin 27 (5V) of the Arduino Nano. This still gives me 10% headroom. Btw, isn't there some limitation with not using the USB supply? I thought the RX/TX pins aren't active if any power source is used except USB (or maybe I don't recall correctly).
As for the original question, what would you suggest to get to the ~85mA?
Edit: Btw, you said there is only 2mA signal from the Arduino. Is this really true? I thought it was MUCH higher but not quite enough for the relays.