Back in March 2018, I decided I wanted to build a lightweight, portable insulator display cabinet to take with me to insulator shows. I had just completed several backlit shelves in my house based on drop-ceiling type LED panels that were both thin and incredibly light. Since getting power at insulator and bottle shows can be a pain, or even impossible in some venues, I started sketching ideas for a battery powered case by combining these LED panels with modern lithium-ion batteries. A few cocktail napkin sketches one night showed that the technology had finally matured to the point that such a thing was not only possible, but also affordable.
My goal was to build a decent looking, light-weight, battery-powered case using off the shelf parts that I could haul around to shows, would look “good enough” on the table, but not be so nice that I’d feel bad when it got the inevitable nicks and dings of being lugged around the country.
The case design takes advantage of modern, high-capacity lithium ion tool batteries – in this particular case, Dewalt 20V packs, since that’s what I also use for all my cordless tools. They’re affordable, readily available, and many collectors I suspect will have them around for their own tools. A 5Ah pack will power the cabinet for about 7 hours – just almost enough to make it through a full show day. Other tool brands of 20V lithium batteries should work as well (as long as you can get a connector for them), but I haven’t tried them or reviewed their internal circuitry to assure there aren’t gotchas. The Dewalts – and their brand cousins Porter Cable and Black and Decker – are very simple: they just connect the positive and negative of the battery to the tool connector, and leave all the safety circuitry to the tool. On the upside, this makes them simple to connect up to things that aren’t tools. The downside is that the vital safety circuitry (in particular, protection against charging and excessive discharge) needs to be in our control board.
The other innovation that makes these cabinets possible is edge-lit LED panel lights for drop ceilings, such as those commonly found in office buildings. It turns out that the 2×2 ft. size is just perfect for what we need. The only catch, again, is that we can’t use the electronics it comes with. We need something that can drive it from a 15-20V battery, not from 120VAC. Fortunately designing this sort of thing is squarely in the list of things I can do rather competently.
The rest of the cabinet is very straight-forward, using parts available at large big box chains. The glass shelves (Dolle #30104) are single source – these seem to be a Home Depot exclusive – but you could also have shelves of similar dimension made from a local glass vendor. I’ve also used Ikea Ivar shelves as sources for the frame lumber, but that’s not a requirement. It’s just that they’re cheap, square, planed and sanded quality block-board project panels that are readily available (at least if you have a nearby Ikea). Plus my insulator display shelves in my house are made out of them, so I had some spares on hand in my lumber pile when I built the original prototype cabinet. Any 12” lumber that’s a hair less than 3/4” of an inch thick will work just fine if you’d rather use something else.
Instructions and Parts
Construction Instructions v1.0 [PDF] (30 May 2019)
CKT-LEDPANEL v2.3 control board schematic [PDF]
Design files for CKT-LEDPANEL control board on Github
Assembled and tested CKT-LEDPANEL boards are available from Iowa Scaled Engineering, or if you would prefer, kits are also available that contain the switch, battery holders, faceplate, and control board.