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RC helicopters consume a LOT of battery power.  Flyers frequently use re-purposed computer server power supplies to provide the DC power to their smart chargers.  But if you use a stack of 12 volt supplies in series, you need a way to keep them organized.  Some people just duct-tape or Velcro the supplies together in a brick, but that doesn't provide any cooling air for the supplies.

This simple wooden rack, made on a CNC machine, does the trick.  It keeps the stack in a compact and portable package, while allowing cooling air to reach the power supplies. 

Step 1: Making the Pieces

To duplicate the way I made these, you'll need access to a CNC machine, such as a ShopBot.  I made mine at TechShop in San Jose, CA. (http://techshop.ws/ That made it easy, but if you don't have access to a CNC router, the design is simple enough that you can make it with just a drill and band saw instead. 

The parts are cut out of plywood.  I used 1/2 inch walnut-veneered fir plywood.  The design is attached as a Corel Draw file and also a .EPS file.  When doing your CAM, cut outside the individual pieces, and inside the elongated ventilation holes.  All cuts should be done with a one-eighth inch cutter, and should go all the way through the material.  The files have six of each part, to make three complete racks from one sheet of plywood two feet square.

Step 2: Assembly and Finishing

Lightly sand all surfaces and cut edges.

Test the fit before gluing.  I made the fit deliberately tight, so the racks could be used without gluing them, if desired.  You will find that if they are just a little bit out of alignment, it won't slide together.  Sand the mating surfaces if necessary.

Because of the tight fit, I was concerned that wood glue would seize up before I had enough time to get everything assembled.  Therefore, I used 30 minute epoxy to give myself more working time.  Apply just a little bit on the mating surfaces so that no glue squeezes out when the parts are slid together.  After the parts are assembled, set the entire assembly on a flat and rigid surface covered with a sheet of wax paper while the glue cures.

It's not necessary, but I decided to make mine dirt-resistant by giving them a light coat of polyurethane finish.  In order to hold the assembly while brushing on the finish, I cut a notch and drilled a hole in a piece of scrap wood, and bolted it to the rack.  After painting most of the rack and letting it dry, I removed my temporarily handle and applied finish to the remaining spot.

Cool project. It's on my list now. Doing research I haven't found specifically why you would want greater than 12V supply to an RC charger. Can you explain?
<p>Some high-capacity smart chargers will accept a wide range of input DC voltage. If you are charging a bunch of large batteries at once, you need a lot of power, or watts. Since watts = volts x amps, you could provide 12 volts with a lot of current (amps), but there are practical limitations with that approach. Another way to get to the same wattage is to provide a higher voltage but not so much current. (Be sure your charger can accept the higher input voltage. Many chargers have a maximum DC input voltage of only 15 volts or so.)</p>

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