I am working on a project where I want to have a 120V hairdryer and a few other things hooked up to an Arduino. I would ideally like it to run on a battery. I know that I could use a relay to step the 120V down to 5V for the Arduino, but I have only seen relays used with something you plug into the wall. I want the whole circuit to run at about 6 to 12 volts. Is there a way to do this?
The Arduino can be powered by 12V because it has a 5V regulator on the board. But, the input/output pins are 5V.
A 12V relay requires a transistor (or other driver circuit). [u]Here[/u] is a solenoid driver circuit that can also be used to drive a relay coil.
You can buy relay boards with the driver built-in or there are lots of solid state relays that can be run from 5V.
I know that I could use a relay to step the 120V down to 5V for the Arduino
A relay is an electrically isolated, electrically controlled, switch. So, you can safely control (turn on & off) 120VAC with a lower voltage & current. Or vice-versa.... You can get a relay with a 12VAC coil and safely control a lower voltage.
It does NOT "step up" or "step down" the voltage. A power supply can give you (electrically isolated) 5VDC or 12VDC from 120VAC. A transformer steps-down or steps-up AC voltage and provides isolation.
I would ideally like it to run on a battery.
A relay coil (for a regular electro-mechanical relay) requires a "moderate" amount of current and may drain your battery quickly while the relay is on/energized. A solid state relay will only require 10mA or so. The Arduino sort-of has a reputation for draining batteries too.
If you don't know much electronics, you really shouldn't be playing with 120V at all. I'm not trying to be mean. It's just that your first surprise could be your last.
I have seen the Power Switch Tail recommended for less experienced people. The device being controlled plugs into the power tail and the power tail plugs into the mains socket. It works like a solid state relay (3V control signal) but requires no modification of controlled devices or mains wiring.
groundfungus:
I have seen the Power Switch Tail recommended for less experienced people. The device being controlled plugs into the power tail and the power tail plugs into the mains socket. It works like a solid state relay (3V control signal) but requires no modification of controlled devices or mains wiring.
I have one of those. You could switch small desk lamps etc. According to the product page, it is rated at 15A (AC I suppose) so 120V*15A=1800W maximal. This following search on walmart.com doesn't look like hair dryers are below rated 1875W:
I'd leave a hair dryer alone if I were a beginner. Small fan = OK, 2KW fan + heater = Not OK
I'd say what aarg said only less concisely and less well-put as aarg put it already.
KatieJD:
I am working on a project where I want to have a 120V hairdryer and a few other things hooked up to an Arduino. I would ideally like it to run on a battery.
A battery-powered hair dryer, or just using a battery for the low-voltage electronics because it's easier than including a 120V-5V power supply?
I have a few other things to answer, but I'm keeping them secret for now. (If you know what else you want to include, why not say it now?)