This UV sterilizer is a very simple design using materials I already had in my garage shop. The only items I needed to buy for this build were the lights, light holders, ballast and piano hinge. I'm hoping that most makers will already have most of what they need to build this model in their shop.
Be safe, both in making the project and using the device. I'll say it again here, 254nm light is dangerous. Read up on it online. Use safety glasses and make sure your skin is completely covered at all times.
We built these designs to try to help keep people safe. The plans are provided for free as open source hardware. The designs are given "as is" without warranty. Use at your own risk.
If you have ideas for improvements, we would love to hear from you. Email Todd at tsampson@cloudspace.com and Michael at michael@cedillas.com.
| Part | Quantity | Price | Total |
|---|---|---|---|
| 3/8" plywood (One 4'x8' sheet - scrap you have on hand is fine) | 1 | $40.00 | $40.00 |
| 1" nails (box has 1000, you only need 100 - I used a nail gun, but standard nails would work) | 1 | $5.98 | $5.98 |
| Wood Glue | 1 | $5.98 | $5.98 |
| Aluminum Foil | 1 | $2.99 | $2.99 |
| Spray Adhesive (I use Super 77, anything you have should work) | 1 | $9.98 | $9.98 |
Build Process Steps
We took a quick measurement of an N95 mask. It appears to need about 10 1/2" to hang freely, including straps. That is why we sized the interior of our box to be around 12".
We measured the T8 bulbs with the bulb holders. A 36" T8 bulb actually measures 36" with the bulb holders in place. As such, we sized the inside of the box to 36" so the end caps are supported by the sides of the box in addition to the single screw used to attach them to the base.
The first step is cutting the rectangular base. While you can make this almost any size that will fit the lights (assuming the lights hit all parts of the item to be sanitized and are left for a sufficient amount of time). The box we designed used the following dimensions:
Base: 36" x 11 1/2"
Sides: 2 @ 14" x 11 1/2"
Back: 2 @ 14" x 36 3/4" assuming you get true 3/8" thick material. If not, compensate for this measure using: 36 + (2 x side thickness).
Front: 2 @ 13 5/16" x 36 3/4" assuming you get true 3/8" thick material. If not, compensate for this measure using 14 - top thickness for the height and 36 + (2 x side thickness) for the length.
Do not cut the top at this time.
In order to have the best light seal possible, the design is built with overlapping joints to help keep in the dangerous 254nm light. (Note: You should always use glasses that protect from 254nm light and have your skin covered while the lights are operational.)
To achieve this overlap, we will take a 3/8" (or thickness of your wood) notch out of 1/2" of the side. You could achieve this cut with a hand saw or bandsaw, but we used a table saw using a sled and stop, then finished the cut with a bandsaw for a clean edge.
The next few images will show this process.
Our table saw outfeed table is also our assembly table. We have dog holes cut into the assembly table at 4" intervals to help with clamping and assembly. We used a clamp and a scrap piece of wood to create a stop for the table saw sled so we wouldn't cut too far. You could use a normal clamp and scrap wood on a regular table to achieve the same result.
I wouldn't attempt this cut without a table saw sled to ensure you can bring the side piece into and back from the blade safely.
Keep in mind that we need a square cut for our notch, so we need to stop the table saw cut with a bit of extra room to create a square end instead of the round blade cut.
Since the bottom side of the cut will get closer to the final cut length, this is approximately where you should stop on the top of the board.
This is what the final notch should look like.
Place the four sides around the base to ensure everything fits as it shown in this image. The front and back should go to the ouside edge of the sides when everything is pressed against the base. The back should be even with the rear edge of the sides. The front should be even with the front edge of the sides where the notch was cut out.
Once the dry fit looks good, you can cut the top. The top is made up of two pieces. The rear piece fits between the sides and fills the space up to the notch that is cut out. This piece should be 36" x 5.75".
The front top section sits on top of the notched out sides and lower front panel. This piece should be slightly large. I recommend 36 7/8 x 6 3/16". If your wood is a different thickness, you can use (36 + (wood thickness * 2) + 1/8) x (5 3/4 + wood thickness + 1/8).
The rear piece will be nailed in place in a later step. Then a piano hinge will be attached so the front section can open. You may want to look at later pictures in the build so you can fully understand how they will go together before making your cuts.
This image shows the rear piece for size, but was taken in a later step.
If you have thinner plywood lying around, use that for this step. If not, the 3/8" will work fine.
Cut the following strips that will be used to create a seal around the lid:
1 @ 36 3/4 x 1"
1 @ 36 x 1"
2 @ 7" x 1"
(Note: This image shows the strips as they are being used in a later step.)
Sand all the parts so they are ready for assemby. (You can tell we used leftover material from other projects based on the splattered paint. Using scrap material won't hurt the project at all.)
Before assembly we applied a single coat of paint to all outside surfaces. This isn't needed for interior surfaces, since they will be covered in aluminum foil, or the glued joints. You don't need to make this perfect now since we will be give the unit an additional coat once it is assembled.
Next we will use spray adhesive to attach aluminum foil to the inside surfaces. Be sure to coat the entire surface, especially the sides and corners.
Spray adhesive smells terrible and can't be great for your health, so wear a vapor mask and work in a well ventilated area.
This is what it should look like when you apply the aluminum foil. Don't worry about imperfections and ridges in the surface, these actually help with light dispersion inside the box.
Carefully, use a razorblade or knife to remove excess aluminum foil along each edge.
Drill a hole in the middle of the back panel approximately 1" from the bottom edge. The hole should be large enough to pass the ballast wires through.
Attach the sides to the base with wood glue and nails. Wipe off excess glue squeeze out, trying to keep the aluminum from getting hazy. I recommend using spray adhesive to put an additional piece of aluminum foil over the edge to ensure the surface is reflective and no light comes out of the gap.
Screw in four light holders into the base so they are in 1/2" from the front and back edges along each side as shown here and in the previous step's picture.
The light holders can be pressed directly against the sides since 1) the exposed metal on the back of the light holder do not have any electric current and 2) all wires are connected to the exposed front of the lighting holder.
Using wood glue and nails, attach the back to the base and sides.
Attach the T8 light holders to the top approximately a 1/2" from the front edge as seen in this image.
Next, install the top by flipping the box on its back as shown below. Put wood glue on the edges and nail into place. Wipe up excess glue squeeze out. Then cover the inside edges with an additional piece of aluminum foil using spray adhesive.
Run the ballast wires through the hole in the back panel. Move the ballast into position as shown in the image. Then screw it into place.
Inside the box, run the three blue wires to the left side of the box across the lower back edge. If you have a stapler, you can use it to secure the wires in place as shown in the picture.
Run one blue wire up the back and across the top. Cut the wire to length (leaving an extra inch or so), strip 3/8" and plug it into one of the holes on the rear side of the light holder.
Run the lower two blue wires to each of the light holders. Staple in place if you have a staple gun. Leaving an extra inch, cut each wire to length. Then strip 3/8" from the end and insert each wire into the light holder side towards the back of the box.
The red wire will be run to the right side of the box. Again, if you have a staple gun, use it to secure the wire in place. Cut the wire to length (plus one inch), strip an 3/8 of an inch from the end and insert the wire into the farthest hole from the front on the lower rear light holder.
Next we will cut strips of aluminum foil, spray the dull side with spray adhesive and use it to cover all the blue and red wires inside the box as shown in the image.
For each of the three light holders on the left (blue wires) we need to create a small jumper wire approximately 2" in length out of the scrap wire we cut off in the previous steps. (Try to take them all from a single cut wire so you can use the longer lengths later.)
Strip 3/8" off of each side of the three jumper wires. Then insert one side of the wire into the side of the light holder with the wire from the ballast. Insert the other side of the jumper wire into the other side of the light holder as shown in the picture.
Press the jumper wires from the last step down gently against the base or top. Using spray adhesive and cut strips of aluminum, cover the wires as shown in the image.
To connect the remaining light holders on the right side, you will create three small jumper wires as you did in the previous steps. You will then use two lengths of scrap ballast wire to connect between the remaining lights as shown in the picture. (See the next step for additional images.)
See image.
See image.
See image. It is hard to tell, but there is a long wire coming into the back and a jumper wire connecting both sides of the light holder as in the other images.
Cover any exposed wires and the rear panel hole with extra aluminum foil and spray adhesive. I like to do a few layers of aluminum foil over the rear hole for extra strength.
Lay the box on its back and attach the front panel using wood glue and nails.
The 36" x 1" strip forms a light seal by being attached to the underside of the lid and offset so it covers the gap between the two top sections. Since this piece is a part of the lid that is inside the box it must be covered in aluminum foil to help with light spread.
We found the easiest way to do this was to spray the back of a sheet of aluminum foil with spray adhesive and roll the strip a few times until the foil is used up as shown in the picture.
Be sure to trim all the aluminum foil off the 1" ends so they do not scrape the inside of the box when opening and closing. (You can always sand down the strip if it is too wide.)
Attach the 36" x 1" strip to the lid using a small amount of wood glue (works on the aluminum foil) and nails. The strip should be centered so that there is a gap on each side of the strip that is approximately equal to the thickness of the wood you used on the sides of the box.
The strip should hang off the back edge of the lid by 1/4" - 3/8" so that it blocks the light but does not hit the light holders that are offset 1/2" back from the front edge of the rear top.
This unit is designed so you can hang N95 masks and other items off a row of hooks attached to the lid. Starting 6 3/8" from one side of the lid space the hooks out every 6" and screw them through the 36" x 1" strip from the last step and into the lid itself.
The remaining trim strips form a light seal on the ouside of the box by hanging down over the space where the lid meets the notch in the sides and front of the box. Position the strips as shown in the picture and attach with wood glue and nails.
Place the lid into position and ensure it can swing open and closed without issue. If any spots are causing friction, use sandpaper to fix the issue.
Next, attach the lid to the rear top using a piano hinge. The hinge should sit flat across the top and be attached with the included screws. Once attached, give a few additional test openings to ensure that the lid operates smoothly.
(Note: This image shows the original design which used small hinges that we already had on hand. We later replaced these with a piano hinge that worked much better.)
Install the UV-C bulbs as you would any standard T8 bulb. Simply insert the two pins vertically into the light holder on each side and turn 90 degrees until you feel it click into place.
We recommend using gloves as these types of bulbs do not like dirt or fingerprints.
The Ballast does not come pre-wired for A/C power. As such, you need to use a spare wire to connect to the power wires coming into the ballast. Once you connect the wires, be sure to secure them with wire nuts, shrink-wrap tubing and/or electrical tape.
Once you are done, put on your glasses and cover your skin. Briefly plug in the unit and look to ensure all the bulbs are working as expected. If not, check the connections. If they look good and you are still having issues, it is probably the ballast. We ended up having a bad ballast on one of the units that needed to be switched out since it was only lighting two of the three bulbs--but was changing which ones at random.
That's about it! Nice job on getting through all the steps.
Here are a few ideas that we are working on for upgrades:
- Automated lid and timer -- You probably noticed that I didn't include a power switch on this unit. That is because we are actually working on a foot control. This would let a user hang masks, click the foot control and have that shut the lid with an actuator. It would then start the lights and run a timer to complete the level of sanitization required before turning off the lights and opening the lid again. This would keep anyone from touching the box itself and needing to sanitize it very frequently.
- Shelf -- In addition to masks, this unit could sanitize a large number of items for hospitals, offices and homes. Doctors could sanitize their stethoscopes along with their masks. Instead of leaving the mail sit for a few days, you could just throw it into the unit to sanitize. You could do the same for smaller packages and groceries. Adding a shelf that lets the 254nm UV-C pass through would make that easy.
- Kill Switch -- Adding a kill switch that automatically shuts off the lights if the lid opens would be a great addition and very easy to add.
If you build one of these units (with or without any of the upgrades listed above), need help with a build or have ideas for improvements, we would love to hear from you! Our email addresses are in the description for this project, so don't hesitate to reach out.