We've gotten a lot of questions about how to use Tessel to control high-power things, so here's a quick guide/FAQ
How do I plug things into the Relay Module?
You can insert and remove wires from the connectors on the board by gently pressing down on the round indentations on the connectors with a ballpoint pen (or similar). No screwdriver required!
NOTE: Whatever you do, be sure that whatever you're plugging in is disconnected from its power source before you go poking at it.
What's Relay Module rated to again?
Current: 5A The relays can conduct 5A continuously
Voltage: 240V We say 240V, when technically the numbers are different for DC and AC (220V DC and 250V AC). In practice, this means that the relays are capable of safely switching wall power.
Power: 60W The relay's rated switching power is 60W, so nominally you shouldn't use a single relay to control anything that uses more than 60W
Can I use the Relay Module to turn my XYZ on and off?
Probably. The 60W power rating is good enough for small things like lights, fans, small appliances, and midsize motors.
Although things like hair driers, toasters, and vacuums are almost certainly out of spec, in practice, we've found exceeding 60W by a little bit to not be a big deal: the fridge in our office is controlled by a Tessel + Relay Module without any problems.
If you really need more power and want to be safe, you can wire relays in parallel. If you decide to go for it with a high-power device, the worst that's likely to happen is that you'd need to buy more Relay Modules because the first one smoked.
If you don't want to risk breaking your Relay Module, you can buy one of these instead and control it using a GPIO pin.
Wait... You said 240V and 5A, but only 60W. What gives?
First things first, let's all get on the same page with how we define power.
In our case, electrical power, measured in Watts, is equal to the current multiplied by the voltage:
P = IV
If you're thinking that the 60W, 240V, and 5A ratings can't possibly all be true at the same time (240 * 5 = 1200 > 60), you're right.
In practice, you should only approach one of the voltage/current values at any given time whilst staying within the power rating.