2016-01-24: BOX OF POWER

My Losmandy GM-8 telescope mount, of course, is capable of moving the telescopes mounted on it so they can track along with the Sun and the Moon and the stars. It uses 12VDC power to do it. I bought a battery and charger to run things off of a few weeks ago, and got the box I decided to try and use for the power box a week or so ago. One day I drew the fifth iteration of what I wanted the inside to look like (below), and cut out some pieces of cardboard to get a rough idea of how things would look. The next day I followed none of it.

Some day when I am rich again I plan on having two batteries for this system. That should supply plenty of power for a full night of observing with enough left over to run the alarm clock in the morning. The battery on the left is a Tenergy 10Ah LiFePO4 battery. On the right I'm using as a standin a burned out Pb-Acid battery from a UPS that I found in the lab waiting to the recycled. On the outside they are identical, which is what the sellers of LiFePO4 batteries are going for. The box is a Pelican Storm Case iM2100.

Most of the original plans had a compartment for the batteries, a compartment for the charger to be semi-permenently contained in, and then the rest as a place for the mount's digital drive system and cables. Getting the power out of the box and to the mount always pointed to mounting the power receptacle connectors in the lid. The sides of the box are not that tall, and I could have either taken space away and built something to protect the wires going into the backs of the connectors, or have let stuff keep hitting the wires and celebrated the 4th of July at some point.

Used my guide to get a profile of the shape of the box. It's the part in the lower left side. The walls slant in a little and then are curved at the bottom. Nothing is ever straight up and down, but this made it easier.

I used my scroll saw to make a few square corners, cut two pieces, and make the curvy bits out of a piece of 3/8" thick narra that I had. I tried to countersink the holes for the three screws to keep the two pieces in the shape of an L, but narra isn't really that kind of wood. They came out a little chewed up. That's OK. It's just a power box.

Anyway, I got it glued and screwed and clamped up against a piece of wood with a square corner. I let the glue dry for a few hours.

The Wall was fastened to the box with three wood screws coming up through the bottom of the box, and one screw at either end through the walls of the box. Just those few screws made it more secure than I thought it would. The pieces are about 3/8" higher than they should be. When the lid is closed they will push up into the lid foam a bit which will keep connectors and other metal bits outside the battery box from getting inside the battery box while transporting.

Next step was the electricals. I don't mind cirgarette lighter plugs, but being a field technician for seismic crap all over the planet has proven the need for secure connections -- over and over again. Amphenol connectors, while a bit expensive, won't let you down. The ones I decided to use were four pins/sockets, and were 'size 12' making them a little under an inch in diameter. They're easy to use with gloves and pretty kick proof. I used two gaskets for the connectors to layout where the receptacles would go.

A few minutes with a drill and off we go. The big holes are 3/4".

More than a few minutes with a wirecutter, soldering iron, heat shrink tubing, crimper, zip ties, small wrench and a screwdriver and things didn't look too bad. Those two 'mounting bases' for the zip ties to anchor the wires to were a good find. I cleaned off the areas with a little alcohol before sticking them on. They ain't coming off any time soon. They are really stuck.

Very nice. Hardly even looks like I did it.

Last thing to do was to convert the battery charger and the power cable for the drive system to the 4-pin connectors. The charger had a plastic connector, so you could connect other things to the charger, but came with a connector and a wire that ended in small alligator clips for connecting to the battery terminals. Snip. The drive's power cord ended in a male cigarette lighter plug. Snip (no medical procedure implied). In the end the meter test and the smoke test indicated I'd managed to keep the polarity of everything straight. The battery and charger combo can handle reversed polarity -- it just won't charge -- but I'm not so sure about the drive system.

Back to arts and crafts for the foam. I sculpted a two-bay piece of closed-cell foam only about 1-1/2" thick to help keep the batteries in place. I didn't want to encase them in foam to prevent them from getting hot when charging, and there needed to be a bit of room around them to run the wiring. The holes were cut badly enough that they keep a good grip on the batteries. I had to use two pieces of cardboard as shoehorns to slide the second battery into place for testing. Good fit.

I used one of the pieces I cut out as fillers in the future battery's hole. With the wires hooked up I guess it could be considered an air cell.

A little measuring, and a little trial and error, and the floor of the rest of the box was covered with a 1/4" thick closed-cell foam.

It all fits! I figured all of this stuff should be in the same box during planning, because you are probably not going to be using the drive system without a battery, or vice versa. The cables are under the system and hand controller boxes. The charger is in the narrow area just this side of the battery box. I cut another piece of the bottom foam and put it on top of the two controller boxes. When the lid is closed it pushes that on that a little bit and keeps everything in place. I took the piece of lid foam I cut out of the corner for the receptacles, shaped it and flipped it around. It stays stuck by itself. When the lid is shut it holds the battery down. When I get two batteries I can just move it over a couple bumps and it will hold down both batteries.

So that's almost it. I have two dust covers that snap on to the receptacles to keep out...well...dust. They are old ones and the rubber inside of them has turned to rock. I'll get some neoprene and get them attached. (They are now on.)

You may have noticed there are no fuses in the wiring. I have two standard in-line fuse holders, but I'm not sure I like them. The wire is a little cheap/stiff. I'll try to find something else. If I can't I'll just go ahead and use them. They'll just need to be stuck in with crimp connectors. (Found better ones. They are in place.)

A built-in voltmeter would have been nice, but I haven't found one I like, or can find room for. I carry a Fluke with me anyway, so there's no real need. On top of that the voltage profile of these batteries is pretty flat until they are almost dead, so watching the voltage really doesn't do much good.


2016-04-24: Decided to prolong poverty a bit and get the second battery. Now it's finished.