Check out the video above for a quick look at the project. The video below shows you in detail how to build it!
Recently, I had been thinking about emergency lighting. In the case of a blackout, the first thing a person needs is light, even if it’s just to get to your junk drawer to find a flashlight, which probably has dead batteries anyways!
So, why not use some good quality rechargeable batteries I already have!?
Ryobi 18V cordless tool batteries are excellent for all sorts of projects, and have quite the dedicated following. I have plenty of these batteries and chargers to match.
For this project, I’m using an all-purpose LED light which is commonly sold as off-road lights for trucks. One important feature is that they can run off a wide range of voltage. For example, these https://amzn.to/40WOYyp LED pods can run anywhere from 9 to 30 volts! Perfect for our 18V batteries.
Next, I needed some way for the light to turn on automatically.
A simple automotive-style 12V relay provides the solution. Relays typically use a low current to activate a higher power second circuit. BUT some relays have both a Normally-Open AND Normally-Closed. The Normally-Closed terminal COMPLETES the circuit UNLESS power is running to it.
I used a low-power, generic 12V DC power supply to convert AC wall power to DC power to keep the circuit open (OFF) UNLESS the power is lost! Then, the spring inside the relay pulls the conductor inside to complete the circuit. When power goes out, the light comes on!
3D Print
To house all the parts, I created a 3D print.
I didn’t start from scratch. Rather, I began with an existing design which already did a nice job of mounting a Ryobi 18V battery. From there, I modified it to add an area to mount the relay, a place for a 3-Way switch, and a hole for the DC input jack.
After printing, I removed the supports, and then added the switch, relay, and DC input jack.
A pair of Keystone 209 Battery clips (https://amzn.to/3U6kgAx) connects directly to the 3D print. I simply had to solder some short wires to them to go to the switch and LED pod.
The wiring in the project is pretty light gauge. I only had to match it up with what was already on the LED pods, which appeared to be 20 AWG. The lamp only draws about half an amp, so no need for heavy wiring.
Wiring
The wiring itself is pretty straight-forward. I mostly used 1/4″ crimp-on solderless connectors.
The positive battery connection goes to the center of the switch.
The two wires from the DC input go to the two side terminals of the relay. (85,86)
One of the outside terminals of the switch goes to the common terminal of the relay. (30)
The third terminal of the switch just needs a short piece of wire coming off of it.
Lastly a wire will go from the center terminal on the relay (87A) and then get soldered or wire nutted to the bare wire from the switch AND to the positive wire of the LED pod.
The negative wire of the LED pod is soldered to the negative Keystone 209 connector to the battery.
The LED pod has a 3/8″ bolt which goes through the smaller hole in the lid. Its power cable goes through the larger hole. It had more cable than needed, so I stripped back the sheathing and cut the power leads shorter before soldering them.
Testing
At this point, I could set the lid in place, add a charged battery, and test it out.
I plugged in the DC power adapter to the wall and the light.
Turning the switch from OFF to the ON position, the LED lights up! Flipping it to the other ON position does nothing, the light stays off. But if I then kill the power (either by unplugging the DC power supply or having a blackout) the light comes on with a click of the relay!
After testing it out and seeing that everything was working to my liking, I used a few drops of SuperGlue to glue the lid in place. If for any reason I still needed to get at the wiring, it IS accessible, as there is no bottom to the case. Everything is simply closed up when the battery is in place.
Home Use
After dark, I tested out the project in my kitchen. Our house has an open conception kitchen and living-room which is the main space of the home. I placed the light up on top of our cabinets and connected it to a switched outlet, so I could quickly and easily turn off power to the light for testing.
Sure enough, the light comes on and gives a bright, wide area of illumination. It’s just a single point of light, so perhaps not the most flattering, but it’s bright and very functional. I even made myself a grilled sandwich for dinner on our gas range, which could be match-lit in a power outage. The light was far more than sufficient for cooking and other activities.
So far, I’m really happy with this project!
I may still make a few more changes. In the first version, I had a hook on the lid which wasn’t very sturdy. It broke off immediately after I took all my photos of the project! I changed the design to a more triangular shape, which could use a carabiner or loop of rope for mounting. I figured that because the lid is the smaller part, it makes more sense to modify, and I may even do a version to mount directly to the wall.
Parts List:
LED Light: https://amzn.to/3JSX18q
ON/OFF/ON Switch: https://amzn.to/3Ket1Fo
Relays: https://amzn.to/3TNGcQZ
1/4″ Spade Quick Disconnects: https://amzn.to/40sUfhl
DC Input Jack: https://amzn.to/3TQ5XQE
Keystone 209 Clip (Ryobi Battery Contact): https://amzn.to/3niCC56
Any low-power 12V DC Power Adapter, for example: https://amzn.to/40eKNOx
Just make sure the size of the power adapter matches the DC input jack.
Also needed: Soldering iron, solder, 18-20 AWG stranded wire, wire stripper, wire crimper.
This project was printed on an Ender 3 S1 3D Printer: https://amzn.to/3LY1h9B
The .STL files are posted at: https://www.thingiverse.com/thing:5948642
and also at: https://www.printables.com/model/441987-ryobi-emergency-light
A couple final notes about this project.
YES, it uses energy while “Off”!
A typical relay like this will draw 150-200mA. Coming through a DC power supply, that’s no more than 2.4 Watts. That little bit of energy use is the price we pay to always have a light ready to come on automatically. It’s also a TINY amount of energy compared to standby losses in off-grid inverters or any other whole home automatic emergency equipment.
Of course, devices like this already exist.
Ryobi makes a battery-powered area light which comes on automatically when the power goes out. (https://amzn.to/3ZGTeB4) Unfortunately, it also costs about $80 USD retail! Not only does my light cost a lot less to build, it’s also fun to figure out the design and actually build it myself!
Lastly, the DC power supply does NOT charge the battery. Designing it to do so would add another level of cost and complexity to the project. Besides, I already have plenty of batteries and chargers. All I need to do is put a charged battery into this light. If I want to take it with camping, etc., all I need to do is put in a fresh battery before restoring it to its job as Automatic Emergency Lighting. I would then put the used battery on charge and add it to the rotation with my other power tool batteries.
I don’t foresee any issues with standby losses or the like, but it’s probably a good idea to check the light once or twice a year. Maybe just test it while checking the batteries in the smoke detectors.
Until then, stay charged up!
-Ben Nelson
PS: Some of the photos show my prototype version of the light.
The lid has the hook, and I was using a spot-light instead of a floodlight.
