Utility box version 2.0

 As mentioned in an earlier post, I had originally intended to use a small (5000 BTU) window AC to cool

the trailer.  This would have been fine - it would have been more than enough air to keep the trailer cool even in an Iowa cornfield, but it was a bit bulky and would have required more than a little creative ductwork.  And it would have necessitated what I came to realize was a truly ugly box.  As I was debating myself on the merits of this design, I came across another ad for the Zero Breeze Mk II, which was designed for cooling a camper, tent or similar.  It's small, very lightweight (about the size of an old canister vacuum, and best of all - it runs on 24vDC.  That in itself improves the working efficiency by 15-20% (no need to convert battery to AC).  Yep, ordered one and received it in about 10 days.  Perfect.

With that in mind, I took a fresh look at 'the box'.  I'd never liked the big black box, but it seemed a logical choice due to the space requirements.  I decided to design one that followed the lines of the trailer, and was a bit smaller.  After carefully measuring the Zero Breeze size, and made the box large enough to hold it and maybe a screen porch.  The new box size also means that I can drop the bike rack a few inches lower, which will improve driving - getting them down out more out of the air flow.  I was mostly able to use 'scrap' plywood panels to build it.  The floor is dominoed together from two pieces of 3/4 BB, and the sides are 1/2¨ BB with oak stringers.  I added blocking in the center and along the edges for a little extra surface area. 

Next trick was to skin the box and wrap it.  I first wrapped the top and front with 1/8th¨ BB, cutting strips around the knuckle rather than trying to bend the plywood in a radius it really wouldn't have been happy with.  I then 'doped' it with penetrating epoxy. For the next step, I started to bend the diamond plate just by leaning on it, which worked somewhat, but I was concerned about having it spring back and whacking me in the face.  I chose a more time honored technique - screwing it down to the top, adding holes every 4 inches along each stringer, and bending it around the curve as I went.   

I used some of my collection of canoe straps to pull it snug, and worked around the curve to get it to conform.   Many more Kregs screws to hold the top in place (because I had lots of those and not many stainless countersunk #8s.  I'll go back and replace the Kregs screws with the #8 stainless and stuff a little sealant into each hole as I install them.  

The end panels will be covered in the left over scraps from doing the sides, and the Seaflo hatches will get added as soon as the ends go on.  The seams will get wrapped with aluminum over sealant over tape later this week, and the whole thing sealed into the body with butyl, trim and mechanical fasteners.  

So now I have this great box and will wrap up the install this week.  And here's the humor for me - I had
really not contemplated how much sheer volume is consumed by 4" ductwork!  With three ducts emerging from the Zero Breeze, two into the cabin for cold air and return air, and an exhaust vent, they occupy a *lot* of real estate.  It's not glamorous, but they got handled and still left enough room for tools.  Also, the Zero Breeze has a set of slots on the bottom that conveniently fit a 1/4¨ carriage bolt, so that will get locked down too.   

Expect one more post on the AC and tongue box.  It's still a work in progress, but I am down to the last bits in prep for a 12 August shakedown run!

Agile Development

Especially for those in the IT world, the term ¨Agile¨ is usually met with both joy and trepidation.  Done well, it's one of the best things that has every happened to project management, software development, and well, almost anything.  However, it's rarely done 'well', and we'll leave it at that since this is a family show.

This project is possibly the most agile project I've ever done.  Everything about it has been an iterative design.  Almost nothing is exactly as I originally sketched it out, and design goals have shifted as I learned new things.  There are also things like the A/C system I mentioned in an earlier post that drove a major change in the front end, and the ripple from *that* change has kept on giving all the way to the back of the trailer.  In some ways I wish I'd waited to order the inverter - I originally bought with the expectation that I could run the house AC unit on battery for a couple of hours a night and recharge either via solar or plug-in.  Since the new AC runs on 24vdc, I now have a 2500 watt inverter to run the Instant Pot, and to charge laptops.  Just a little overkill, I think.  But it's bought, paid for and too long out of the box to return, so I'll bolt it in anyway.

The board above will get screwed in to the back of the bay.  The batteries will mount on the floor, taking most of the clear space at the bottom.  What's not shown here (future post) is circuit protection, AC switching, the master switch, etc.  That's all going up above the counter where they can be accessed without performing contortionist routines.  And I still have to balance and assemble the battery pack and BMS - not hard, but somewhat tedious and it does require a certain amount of care to avoid arc welding with your fingers.  At the end of the day, I'll have 100aH 24volts of LiFePo4 battery stuffed behind the wall to power all the creature comforts.