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Hi Brett
I've just been doing this exercise and have measured a couple of things.
Mount - most draw under an amp when tracking, but that spikes when slewing (hopefully little of this while doing long imaging runs). Allow 1amp draw.
Camera - Most internal batteries are ~1000-1500mah and last for ~1-2 hrs of long exposures. If you extrapolate this to what a 12V adaptor would consume, you're probably looking at another 1amp.
Laptop (the killer) - my 15inch laptop draws a maximum of 3.25amp at 20V. I measured the draw from the 12V adaptor at ~6amp. This was whilst turning on with a flat internal battery. Hopefully with a charged battery and computer running a moderate workload with screen dimmed, this may reduce to ~3amp draw from the 12V battery.
Already you're at 5-6amps. What about dew heaters - another 3-5amps.
If you plan to use an inverter to produce 240V power and use your normal laptop & camera adapters, your inverter will be ~80-85% efficient, so add another 2amps to the calculations to be safe.
I'd estimate my setup will draw ~10amps (including dew heaters). In winter, starting imaging at 7pm and finishing at 3am, I'll be looking at 80amps. Big & heavy batteries are called for...
DT
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