I spent about half the weekend putting what I think are the finishing touches on my electrical system schematics, at least for now, and making a shopping list of components to buy. Tomorrow I'll place the first order with B&C for wire, terminals, fuse blocks, and stuff like that. Luckily I don't have to buy the really expensive stuff (e.g. alternators) just yet.
The latest revision of the drawings is here.
I ordered and received my second aux battery, a Panasonic UP-RW1220P1. This guy is designed for UPS applications, which is basically how I'm going to use it. It's a little larger than the previous one I was messing around with, but the flatter shape of it actually gives me more options for mounting. It also has 1/4" connectors instead of the flimsier 3/16" ones on the other battery, which is a bonus.
This is the battery tray I made for it. It's all made from 1/16" aluminum angle. I actually started out intending to build it out of 1/8" angle, but it became apparent that it was going to be horrendously heavy and overbuilt that way. Since I'm building an airplane, not a Soviet tractor, I scrapped what I'd done and built this one instead. I was peeved at throwing away half a day's work, but the final version turned out pretty nice.
It's mounted beneath the floor on the passenger side of the baggage compartment, in the wedge-shaped bay just outboard of the strobe power supplies. I attached the side angles to the floor ribs with blind rivets, then shot and bucked the round-head rivets that attach the left wall of the tray since there was no way to get a squeezer down in there. First rivets I've shot in approximately forever.
Here's the rest of the pieces installed with screws. Like a ship in a bottle, I had to make it able to be disassembled so I could put it together inside the fuselage and still have good riveting access.
The hold-down bar is another piece of 1/16" angle, with one of the legs cut down to about 1/8" wide to clear the baggage floor above. The bolts are AN3-12A's.
Here's a perspective view showing exactly where in the airplane the aux battery is located. It's getting quite cozy in there under the baggage floor.
If you look at the datasheet linked above, you can see that the battery's terminals are on the side, which made the design of the tray a little more complicated than it should have been. The right-hand wall of the tray has a notch cut out to provide plenty of clearance around the positive battery terminal. The negative terminal has enough room around it to get the FastOn connector over it, and beyond that I don't really care if the ground wire touches the airframe or not.
Went to Harbor Freight and picked up another box of rubber gloves and a new air hose, since my last one sprung a leak. Oh well, I got three years or so out of it. I also installed a swivel thingy on the output of the air regulator, to keep the hose from trying to break off the regulator's outlet fitting.
As is usual when I go to Harbor Freight, I couldn't resist buying something cheap that I didn't really need - this time it was a drill press vise for nine bucks. And, as is typical, it's really crudely made. I followed John's advice and replaced the rusty, jagged steel jaws with thin strips of wood, which makes it way more useful for holding aluminum airplane parts.
After thinking about my chosen battery location some more, I decided that it involves too many compromises, so I'm not going to use it. I found another battery that actually has more capacity and will fit better, in a different location in the airplane. Stay tuned.
Meanwhile, I updated my electrical system design document - the latest revision is here.