Let's talk about Juice. "If I were going to take the telescope into
the field, this is the way I would do it."

December 7-8.

I dragged the Xantrex 600 battery and inverter out of the basement and cleaned it up. It occurs to me that I've never put it under a realistic stargazing load and timed it to exhaustion. I removed the top to see what size battery to shop for, thinking I might need to put a better, newer-tech one in it. Well, think again. First, it already has an AGM battery. "40AH" it says. Second, the innerds are as clean as the day it was manufactured. Very impressive. Nothing looks cheap or half-done or cobbled together. "Designed in Canada," the label says, "Assembled in China."

A voltmeter says it's still pushing just under 14v; the external charger lights up green ("ready for action"). I'm charging it this afternoon using its fancy charger (OK to store attached and on; allow 10 hours for full recharge...) and will give this a try tonight as the sole power for the G11 / ST2000XM / Vaio imaging rig. Then, no matter how it goes tonight, I'll charge it all night and all day and try it again tomorrow. FWIW: the original battery is a Topin TP12-40B The battery is 9 inches high (critical), by 8.5 inches long, by 5 inches wide with vertical blade posts (flat tabs with bolts for cable attachment through them). There's room in the case for a battery up to another inch longer and wider (just remove or adjust the foam spacers), but now 'm thinking that for more run-time, I could easily hook a second battery to the external power posts. I photographed the inside of the case for reference. For charging in the field, suitable solar panels are affordable these days (especially if I don't need to buy a second battery). Wind turbines, anyone? How about a generator powered by a falling rock? That would be wonderfully sisyphusian.

Let's guess that the ST2000XM is going to draw on average about 3A. The Vaio about 4A. The G11 about 1A (the RA plus electronics pulls 500mA; even a constant run on the Dec axis would not double that, so 1A is max). The powered hub? Say 1A tops. The power bricks for all these things say they are going to draw more, but will the bricks emit more power than is drawn? It has to go somewhere, and they do get warm. Do they get that warm? Oh, I hate having superficial lacuna in my physics memory exposed! Anyway, at a guess, 9A total draw. Plus losses at the inverter, because I'm just going to plug in the outfit I've been using, power case and all. Place your bets. 4 hours? 3?

Answer for tonight is... 1.5 hours. I hunted some for the Veil, found it, acquired three images, watched tree-limbs begin to streak across the frame, and launched Guide to decide on a new target. Then the ST2000 disappeared from the system and Maxim couldn't reconnect to it. Drive commands might have been squirrelly for some time before that, but with clouds and trees and high winds... who could tell? When I got out to the outfit, the red "no power remaining" light was lit on the side of the battery. When I brought the Xantrex inside, a voltmeter across the posts showed 12.0V and the "battery state" indicator wouldn't light even the bottom red light.

The battery was only charged for 3 hours after sitting for a couple of years, so this is hardly a representative trial. Temperature was 28F. The CCD cooler was running 65% to hold -35C.

I'll do another rundown test tomorrow evening, under the stars if possible, under the clouds if not. Once I know how long things can be operated in this mode, I'll try running the ST2000XM off the DC power posts instead of going through the inverter. That's about as far as I can go -- the notebook has to be powered somehow because I know its internal battery won't carry it through a night-long imaging session.

 

 

Note vastly improved cable management
(also ever-helpful dog in the background).

 

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Text & Photos by David Cortner
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