daytrader152:
The relay is Songle SRD-05VDC-SL-C. It is rated at 0.36W, so the current consumption is around 72ma. This seems a bit high and strange because I can control the relay just fine with my Arduino UNO.Because you can does not me you should. You risk real damage to arduino pins drawing that much current. Why don't you wire a relay coil directly to +5vdc and take a current measurement with your DVM. That will give you the answer and the point you to what devices can provide that much output current.
I am powering up my Arduino using an external 12V/15A supply. I will likely need another external 5V supply just for the relays since 72ma x 45 = 3.24A, which is greater than 1A rating from Arduino 5V voltage regulator.
But earlier you wrote: "I need to control 360 5V-relays with my Arduino (only one relay will be active at one time)." So now you are going to power how many at a time? If you are only going to power one at a time on then it would seem to be very uneconomical to size a power supply that could power all of them at one time?
Lefty