Sunday, April 3, 2016

A Battery Box Addition

The Battery Box got one refinement over the last couple of weeks: A built-in 7.5VDC power supply.

I had intended to use an external supply, but the little Drok unit gets good reviews and is much smaller than the adjustable supply I had planned to use. It was perfect for mounting within the box. All it needed was an output plug. For that I went with the same sort of plug used on many mounts, a lockable panel-mount socket and plug. (Both were purchased on eBay.)

Drok 12VDC to 7.5VDC step-down converter
5.5x2.1mm socket and plug
A built-in converter presents two problems if it's left connected to a battery: A continual power drain (0.1 to 0.12W) and possible interaction with a smart charger. The drain doesn't sound like much, but it equals about 7Ah per month; that's a lot for a 35Ah battery. To prevent these problems I isolated the converter using a rocker SPST switch. As a reminder to turn off the converter when it's not needed I added a tiny LED that draws a minuscule 3mA. Here's the switch and LED:

Switch and indicator light

As I said, it's a tiny LED! It's just bright enough to let you know that the converter is active.

12V sockets (above) and new 7.5V socket (below).
I made an extension patch cord that fits the plug and the power cord from the camera's dummy battery; this will permit me to use other power supplies.

One other add-on is intended to make this easier to use: An accessory cable for my charger that will let it charge through one of the sockets. Because this is a small battery it can be charged at a relatively low amperage of 1.1A. While I haven't yet recharged it from a state of deep discharge, I'm hoping that it will remain cool during charging even when left in the box. It's my hope to never need to remove the cover.

NEXT UP: It's the Messier Marathon, April 8 or 9! I plan on imaging some Messier galaxies as a part of the Arp galaxy imaging project. There are six Messier/Arp galaxies I haven't imaged yet: 49, 60, 65, 66, 77, 87, and 90. Only 77 is badly placed; it will set too soon for imaging. Because it's a marathon night, I'll shoot only luminance with my ST-8300M, and probably only an hour apiece at most using my TV102. Last year the MM had only so-so skies. Here in Minnesota we're overdue for some good Messier luck.

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