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Thread: Control AC Mains voltages

  1. #1

    Control AC Mains voltages

    Sorry if this is a FAQ, but I'd like to control grounded AC mains devices with a teensy 3 (3.3V). Obviously I can just use a relay with a low enough coil current and a high enough rating. However, I'd rather not do this wiring myself, mostly because the devices controlled are fairly inductive (heaters and fans and ballasts) and will be in use while I'm not at home. Maybe I'm just being a ninny?

    I'm wondering if there's a cheap device I can buy that will contain the relay and will be properly grounded. I'd prefer something small (say like the size of an iphone charger but grounded) that fits inline with the power cord.

    I see a number of boards for this:

    But I'm hoping for a complete product with an enclosure. Water-resistant might be nice as well.

    Anyone found/used something like this?

    If I do make a PCB that operates at mains voltages, do I have to be particularly concerned about trace width, etc?



  2. #2
    Senior Member Constantin's Avatar
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    Nov 2012
    In the yard with a 17' Dia. Ferris Wheel
    I'd give line voltage devices the respect they deserve. For example, my power monitor eschews the common practice of tying line power directly into the MCU via a couple of drop down resistors and uses a transformer instead.

    Anyhow, for your application, I'd stick to the power tail for the simple reason that it's fully assembled and has a easy to use NEMA 5-15 plug / receptacle.

    You may need to use an external transistor to drive the device, double check on their instructions to be sure that the Teensy can supply the required mA. IIRC, the older version of the tail needed such a transistor, even for a Arduino and those AVR MCUs can provide more current than a Teensy 3.

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