Okay, so I'm using an Arduino Uno R3 and I wanted to start of my own home automation project. I have a 4 channel 12V relay board and I normally connect it to a 12V 500mA adapter. What is the maximum wattage bulb (or CFL) that I can power with this configuration?

  • The ampere rating should be printed on the relays. Watts = Amps x Voltage
    – Gerben
    Commented Dec 7, 2014 at 15:43
  • @Gerben. Thanks for the heads up! It says 5A 240V AC and the coil is 12V DC. Commented Dec 8, 2014 at 6:54
  • Than that's 1000Watt if you're on 220V AC, 500Watt if your on 110V AC (e.g. US). Good luck finding a 1000Watt CFL :-P
    – Gerben
    Commented Dec 8, 2014 at 16:16

1 Answer 1


Unless you feel like starting a fire, none. Find a 220V 2A relay with a 5V coil and use that instead, switching the hot wire and not the neutral.

  • Huh? If the OP builds a circuit to switch 12v (with a flyback diode) why would the relay board in question start a fire?
    – Duncan C
    Commented Jan 7, 2015 at 3:11
  • @DuncanC: There aren't many CFL bulbs that run on 12V, and the asker hadn't given the contact specifications yet. Commented Jan 7, 2015 at 4:23

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