Grumpy_Mike:
because the coil in the relay is going to suck a lot of current isn't it?
Depends on the relay but 20 to 100 mA is not a lot.
Are these typical relay currents? I'm looking at automotive relays because they seem to be whats needed to go up to 15 A (Most seem to be 30 or 40 A). I am making this up as a go with part selection. Also with regard to controlling a relay, I'm guessing I just connect it to my 12V lead acid battery and switch it with like a 2N2222. Do I need some kind of resistor? Or is the coil resistor typically enough to get the current down? They seem to show coil resistances of like 10-50 Ohm, so I'm kind of raising an eyebrow to this 20-100mA range.