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Battery-powered sconce hack

After we finished our kitchen we realized that the spaces above the counter and on either side of our new window seemed a bit bare and since we also only have overhead lighting in the kitchen we were looking to fill the space with a pair of sconces.

That’s easier said than done though, since the kitchen is complete — meaning that if we wanted to run electrical we’d have to open the walls up again. So I did some thinking and came up with a rechargeable battery-powered solution that is super simple to put together, and has up to 55 hours of run time between charges!

Supplies

Beautiful Long Made Co. 8” Brass Sconce

Tools

  • Leatherman multi-tool

  • Drill and drill bits

Nice to have

  • Hot glue gun

  • Soldering iron, solder, and flux. We didn’t need to do any soldering, but if you break any existing soldered connections its nice to be able to repair them.

Disassembly

We took apart our sconce, making sure to note the order in which we unscrewed things. There were two nuts holding in the cord wires that were loosened to complete the disassembly.

Rewiring and testing

We cut and stripped of some of the lead wire going from the junction box to the lights themselves since it was much too long. We then wired each light to the junction box. I popped off the cover of the IR switch to reveal the electronics and sensor inside, which was pretty convenient to place over the hole for the original cord to serve as a means to turn the light on and off. The junction box, switch, and the battery pack both just plugged into one another with a standard 12V connection. We made sure to test the function of the lights before stringing it all through the light fixture.

Finishing up and mounting

I had to unwire the lights from the junction box to string them through the fixture. I left the original bulb holder (minus the actual screw-in part removed earlier) so I would have something to stick the puck lights to once the wires were through. I reconnected the leads to the junction box and tested the lights again — just to make sure! I drilled another hold in the semi-flush mount part opposite of the existing hole for the original cord so that I could string the 12V charging cable from the battery pack out the top of the fixture, which will make for easy recharging without having to remove the fixture from the wall. I also glued the sensor in place over the other hole at this time. The next step was to peel the sticker-backs off of the puck lights and stick them on the bulb holder.

I then built a wood case that could hold the battery pack in place inside the wall, and then I knocked a hole in the wall so that the battery and wood case fit inside.

 I connected all of the 12V plugs to one another, and then carefully hid the wires in the wall, strung the charging cord out of its hole in the fixture, and then screwed the fixture into an existing stud. Popping the shade over the wire spring holders completed the install!

Calculating run-length

Part of the reason we went with this set up is that a traditional puck light with integrated batteries (either AA or AAA batteries) are severely lacking in run-time, and will chew through batteries. A puck light with three AA or AAA batteries in series (for a 2.5-watt light) have 2,500mAh and 1,000mAh ratings, respectively. How much run time is this? An estimate for run-length is given by the following formula:

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Or, in plain English, run time is approximately the charge (in amp-hours) times the line voltage times the efficiency (DC to AC conversion) over the number of lights times their power consumption. Plugging in the variables for a single puck light running on AA or AAA batteries and assuming a DC/AC efficiency of 85% yields run times of 2.8 and 1.5 hours for a single puck light at 100% brightness, respectively. Note: run time probably scales linearly with brightness — these lights typically have step range of 25-50-75-100% brightness.

Our battery pack is powering three lights, and should last 9.2 hours on maximum brightness (which is 3-times brighter than the single light with the AA or AAA batteries from the calculation above!), and up to 37 hours (25% brightness) on a single charge. If we had opted for a single puck light we could have extended this to 28 (100% brightness) and 111 hours (25% brightness) of continuous run time, but the extra brightness is worth if for us. Additionally, since we were able to orient the lights in different directions, it really looks light a real light, and not just a point source of a single puck light.

If you’re looking to achieve longer times than this, then scale up the battery pack — the type of Li-ion battery we got comes in a size range of between 3,000mAh and 20,000mAh.

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