Box your Battery

Tired of lugging a heavy battery around by its carrying strap? Inconvenienced by connecting to it using alligator clamps? Messed up by dew getting the battery all wet? Make a battery box!

It's simpler than you might think and you can make it as fancy as you want. Here's my rather minimalist box:

A Simple Battery Box

At the right side under the lid protuberance designed to allow dew to run off are two 12V sockets. I may add a couple more on the far side. Each is individually fused so that if one device blows the rest keep working.
 

The voltmeter springs into action

The only other thing I added was an LED voltmeter that's actuated by a momentary-on push button. This helps me monitor the battery's state of charge.

Under the hood

The 35Ah battery (group U1) is dwarfed by the box, which is designed to handle batteries in groups 24-31. I've used rigid foam to hold it in place. I haven't done a deep recharge of the battery yet, so I don't know how warm it will get. I suspect it won't get warm at all--My charger is only 1.1A. With an accessory the charger can charge the battery though one of the sockets

What you'll need:

• The box: The one I used comes with a useful divider and can be used with a  battery that provides 75Ah and still have room for the sockets
• Sockets are found on eBay for about $6 each. I used waterproof ones that come with their own cables and fuses. I bought the kind that attach with a locking ring; they've been solid in use.
• The voltmeter (about $4) is also from eBay, waterproof, and also attaches with a ring.
• Connecting wire. If you run your own wire to the sockets, be sure to use 14AWG or heavier wire, and check that the fuses are appropriate for the wire and devices you plan to connect. Wire to the voltmeter can be much lighter as it will carry only a tiny current.
• Tools: The only helpful tool you may not have is a variable drill bit that will help make the socket and meter holes. You don't need one as large as the holes--it can be used the start the hole and ream it to proper size.

What you don't need:

• Battery terminals for jumper cables. This should be a deep-cycle battery, and it doesn't like jump starting. 
• A carrying strap. The box comes with handholds at either end. A 35Ah battery and box weighs under 25 pounds, so it's easy to carry.

As you can see from the above picture a U1-sized battery leaves a lot of room for accessorizing. An amp meter could be useful to install if you want to measure battery drain. If you have the need for other voltages, add some step-down DC converters. They're small and very inexpensive. You should probably isolate them from any charger, perhaps with a two-way rocker switch. Go wild and add lights and a radio and you have one of the overpriced commercial "power tanks."

I'll be field testing this battery over the summer at a number of star parties, and may modify it as a result.

My battery box delivers twice the watt hours of a commercial "power tank," and costs less (about $125 total,  $100 of which is the battery and charger).

Correcting the Too-short Celestron Hand Control Cable

One of the perennial, if minor, "what were they thinking" topics in astronomy hardware is the short coiled cable used to connect Celestron hand controls to their mounts. The cable, stiffly coiled like an old phone handset line, is simply too short.

This wasn't so bad on my old CG5 ASGT where the mount head isn't all that large, but on my CGEM it couldn't be ignored. It was possible to have the handset pulled right out of its tripod leg cradle as the scope turned in RA. That's not something you want to see when you're imaging, since it means the coiled cord was torquing the mount and then letting the handset become a free-swinging weight in whatever breeze there might be.

One solution I tried for a while was a coiled extension cable. The added cable was so heavy and droopy that it was awkward to handle and tended to get snagged on the mount. Then I came across a video that shows how to replace the stock cable with one that's more user-friendly.

All you need is

• A piece of flat 6-conductor telephone cable, preferably one with at least one end having an RJ12 connector attached--if not, you'll have to do that yourself. These can be found many places; on Amazon they're typically around $5 to $6.
• A soldering gun and solder (A good, fast-heating gun is much preferable to the old pencil type)
• A wire cutter
• A craft knife for stripping very thin wires
• Heat-shrink wire tubing (I found this on eBay)

Extremely helpful to have is a soldering jig to hold the ends of the wires together as you solder them.

The most important consideration is getting the wire connections correct. In my case the wire colors and order in the cable exactly matched that used by Celestron, so it was easy to get things right. If you get the connections wrong its quite possible you'll ruin your handset.

The filter from the old cable will be reused on your new cable. Aside from that, you can discard the old cable. Or toss it into your pile of stuff you probably should trash but are keeping "just in case" it might be useful someday.

The job takes an hour or so, when you're done you'll have the kind of cable Celestron should have provided in the first place!

A DIY Binocular Mount

Thanks to a change in plans--a wedding I want to attend is on the same Saturday as the Wisconsin Observers Weekend--I am going to go to this year's Nebraska Star Party. No offense intended to WOW, but NSP is a bit of a bigger show with more people and darker skies. NSP begins as the annual Jeffers Petroglyphs party ends, so I'll be able to save a couple of hours of drive time by going straight from Jeffers to NSP.

But what to do at NSP? I'll have my imaging gear from Jeffers with me, but maybe I should just make my first NSP a strictly visual affair. All that really dark sky, you know!

I've come into possession of an old pair of Celestron binoculars, their 11x80 Giant model from the 1990s:

This is not the model that was labeled "Comet Hunter" or "Comet King" apparently to cash in on Halley's Comet in 1986. What reviews I can find for this later model are mixed.

Good features from my standpoint:

• It was free
• It has a wide FOV (4.5 degrees)
• It comes with a mounting bracket. 

Cons:

• Probably not the greatest optical quality
• Heavy (6.7 pounds) 
• Exit pupil (~7mm) that is too large for my old eyes. I'm 60, and although I haven't measured, I would guess my pupils don't open past 5mm. This means that some of the objective size is being wasted, but some people suggest this has a small silver lining in that one's eyes can move a little laterally and stay in the light.

My past experience with large binoculars suggests that a mount is a very good thing to use for steadiness and comfort. A little googling turned up this plan, which I am adapting to the top of my CGEM tripod. The CGEM tripod has two threaded holes for mounting the azimuth post. These are perfect for attaching a base plate. In my case I'm changing the plan to substitute a 3/4" piece of hardwood for the 3/8" aluminum plate. The rest will be pretty much as the design suggests.

I was unable to find the nice round counterweights seen in the explanatory pictures, so I'm using lead scuba weights from the appropriately named Lead-co USA. Construction begins next week.

An update on May 20: Lead-co uses fixed-cost USPS mailing boxes, and I had paid for a medium sized-one. It turns out that the weights I bought fit in the small box, so Lead-co refunded the difference. Nice!

DIY Concrete Pier for a medium-sized SCT

What do you need for imaging with a Celestron 9 1/4" SCT operating at f/10 (FL 2350mm)? A mount with very little flex. In my case this works out to a Celestron CGEM mount. For a couple of years* now I've been working toward building a small observatory. I want to put the mount on a pier, and miracle of miracles I have actually gotten this part of the observatory done! Not without a lot of dithering about what sort of pier to install.

If you go to Cloudy Nights you'll see many people giving their ideas of what constitutes an adequate pier for imaging at a modestly long focal length. The largest telescope I anticipated using was a 9" SCT, so I felt much of the advice, though sound, was meant for larger loads. On the other hand, I decided that some suggestions were a little on the light side.

Some ideas I considered and rejected were for a pier made from 4x4" wood beams (possible polar realignment needed as the humidity changes), steel pipe piers (expensive), 10 or 12" concrete piers (overkill), 4-6" concrete piers (too much flex).

That left me with an 8" concrete pier as the ideal compromise. Cheap in cost, and easy to put together--even for me.

Materials:

1. Digging things, such as a hole auger and shovel
2. A little small gravel to line the hole bottom
3. Concrete forms
4. Duct tape
5. 2x4" lumber for holding the form level
6. Bagged Concrete (Quikrete, for example) 
7. Rebar
8. Pier to mount adapter
9. "J" bolts with hardware to match adapter
10. Mixing tub such an old wheelbarrow
11. Garden hoe for mixing concrete
12. Bucket to measure water
13. Water

Now, some lessons learned as applies to each of the above:

(1)
The frost line here is 42" down, so the hole must be at least that deep plus a few inches. Fortunately I had an old post hole manual auger that made digging a snap. It looks like this one, which can still be found for sale various places:

Manual Auger

Mine is actually an antique hand-me-down with a decayed wooden hand bar and several layers of rust on the metal parts, but it sliced into my mix of clay and gravel almost like the proverbial warm knife in butter. The only trouble I had was at 42" depth, where it ran into a larger rock (which now sits on a counter in front of me). The hole was deepened to 45" by using a long-handled shovel.

(2)

You just need enough gravel to put a few inches in the bottom of the hole for drainage. Pack it down with a 2x4".

(3)-(5)

Forms are usually available in 4 foot lengths (mine came from Home Depot). Because the total length of my pier was longer than this, I joined two forms by making a 1 foot long external sleeve and putting it all together with duct tape. The length is critical because the adapter will ride atop the form, which will be filled with cement to just below the top of the form. You need to plan things out so that the distance between the adapter bottom and the top of the cement is about 1.5" or so.

The form should fit nicely into the hole with a little wiggle room around it; level it and shore it up with 2x4"s:

Concrete form in place

Then I filled in the gap around the tube with the extracted dirt.  You can use the rebar to get that dirt packed in, and run some water into it to flush it down. (Don't add water unless you're ready to pour concrete; a wet form can lose its integrity in 24 hours).

(6)

You will need to know how much concrete to have on hand, calculated from the volume of the pier and the bag weight you're willing to handle. I was able to handle 60 pound bags, but smaller bags will spare you a possible blown back. I would suggest rounding up the amount you need by one bag, just in case. 

(7)-(13)

This is the fun part. You want everything ready before beginning, so cut the rebar to the right length (an inch or two shorter than the pier. I used one piece of rebar, centered in the pier, but some will say use three. Whatever your choice, make sure the rebar won't interfere with the J bolts.

You have, of course, already determined North, so that you know the way to orient the adapter!

Put together the pier adapter and J bolts so that the assembly is ready to put into the concrete. I used three 1/2" diameter 8" long J bolts (Home Depot) and the Starizona CGEM adapter. In my case the Adapter's diameter was smaller than that of the form tube, so I used shims to hold it in position and maintain reasonable level:

Pier Adapter in place with shims (after has been cement poured)

Now get your bags of quick-mix concrete, mixing tub, mixing tool, and water supply ready at hand. 

Note: Even if you're not using Quick-set concrete  you shouldn't let much time pass between one batch and the next. You won't take any breaks until you've embedded the adapter in the pier top. 

Dump a bag of concrete into the tub, add the manufacturer's suggested amount of water, and mix thoroughly. The common mistake (I've read) is to make the mix too wet, so try not to be tempted into adding more water. In my case I tried to avoid this error so diligently that I made the mix a little dry, but it seems to have worked out. Shovel the concrete into the form, minding the level.

After adding a second bag of concrete push the rebar into the poured concrete so that it's a the right height. You may need to hammer it to the right depth.  

Continue adding more batches of concrete, making sure your rebar remains centered in the form. You may also want to use a long rod from time to time to remove any trapped air pockets that form. When I made my pier I noticed that these pockets tended to form against the inside of the form.

The last batch of concrete should be large enough to complete the pier. Depending on the size of the shim(s), you will fill the form to about an 1.5" from the top. If needed mix in more concrete mix and water. You may want to make the last batch of concrete a little wet so that the J bolts will embed more completely. Shovel this into the form to the level you want and then push the adapter assembly into it. Make sure you have the adapter oriented to north correctly! Level the adapter and you're done!

Clean up your tools and the work site, then take a break. After 24 hours you can rip the form away. At this point inspect the J bolts to make sure they're solid--no wiggling allowed. If they're not, you have a problem. Post a comment if you do and I'll reply how I fixed this when it happened to me. 

Avoid the temptation to put a load on the adapter for at least several days (two weeks would be even better). If the weather is hot and sunny, moisten  the outside of the concrete from time to time and wrap it in plastic.

After a month you can apply a concrete sealer and paint the pier with an outdoor house paint. I went with white, but if fluorescent green is your thing, go for it.

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*Why a couple of years on the observatory? The winter of 2011-2012 was so mild here that I found I hardly needed an observatory. And I was so busy during the summer and fall of 2012 that my talent of procrastination bloomed fully. Maybe next summer I'll get to it?

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UPDATE, SPRING 2016: Still no observatory. There still seems little need for one; I'm doing more imaging at dark sites as the light pollution, neighbors' absurd "security" lights, and tree blockage all continue to increase. The wood planks on the platform have warped, but the pier continues to serve me well. Factoid: this blog entry is far and away the most viewed of all my posts (which isn't saying much).