Do you ever wish your smart plug was a little dumber? Afraid that your clever power monitoring will result in your freezer or server getting turned off because you brushed the entity button with your fingertip? Well let’s solve that problem by breaking it!
This instruction is for bypassing the switching ability of a Sengled E1C-NB7 Zigbee Smart Plug, though the instructions will probably look very similar for most similar smart plugs. The end result is a smart plug that is “always on”, though it will think it is being turned on and off.
Limitation: For this plug, if the switch is “off” it will not monitor power/energy. So for your power monitoring needs you will still need to make sure it is turned on, but at least your device won’t shut down unexpectedly if it is turned off accidentally.
Safety: This modification requires you to work with mains voltage equipment that is expected to carry up to 15A. It isn’t rocket science, but I don’t recommend this as a “first electronics project”. You should have familiarity with your mains system including the ability to clearly identify the hot, neutral and ground pins by sight alone, know how to verify zero voltage safely, and how to test a mains system safely. If none of that sounds familiar, seek more advice or try some other projects first. If your solder joints are bad, or you jump the wrong pins you could create a fire or shock hazard in your home!
Step 1: Break it open! The Sengled is glued shut - no tabs. You just have to get a jimmy/spudger under one of the lips (try a few places to find a weaker spot), then gently pry around until you pop the central core out. Watch out for the parts of the switch which may want to come flying out. There is the switch plate, an extension arm, and a thin insulating tube.
Step 2: Examine the connections. In the case of the Sengled, the neutral and ground are unswitched (correctly), and the hot is switched. The receptacle connection travels along the thick pad over to the relay, then out of the relay, back along another thick pad, and into the back of the plug connection. (The red line on the image). Confirm this fact with your multimeter. We will install a jumper along the yellow line to bypass the relay entirely.
Step 3: Make and solder a jumper. Since this is expected to carry up to 15A for short durations, or 12A continuously, use 14 AWG or larger for your jumper. Stranded or solid core would be OK. Use a bit of flux because you want a very solid solder joint here since the solder will be acting as a part of the circuit (not normally recommended).
Solder in place with a nice hot iron, and use your multimeter to test the connections again. Make very certain that you do not have a short between hot and neutral or ground, or between neutral and ground. Make sure the connection across the hot plug pin and receptacle end is low resistance. Pull on the jumper to make sure it is sound and that you don’t have a cold solder joint.
Step 4: Glue it back together. Use a few dabs of super glue along the edges and re-secure. You want it to be glued tight because when unplugging the unit you have to pull on the outer case. If it isn’t glued very well then you could pull the outer case off and leave yourself with an exposed set of pins sticking out of the wall (the ol’ widow maker). You can see mine looks “almost stock”, except where I melted it a bit with my soldering torch and yanked on it with my spudger. The 2nd one will be much cleaner. Promise.
Congratulations - you broke your smart plug! It now does one fewer thing than it did when you bought it, but at least you won’t do that one thing accidentally and shut off your server rack, freezer, heater, or other thing that you REALLY don’t want being accidentally turned off.