While my observatory is on mains power, the Grose Vale area has been prone to blackouts from time to time. In the past few years I've had 3 extended outages and several significant fluctuations while imaging. Accompanying these is the risk of power surges - potentially lethal to your prized equipment! With my mount having to go back to Japan because of a blown encoder (??caused by a surge perhaps??), I decided it was time to give my obs a clean and uninterruptable power supply.
I assembled a simple, DIY online or dual conversion UPS (as opposed to a standby or line interactive UPS). Not a new idea by any means - see
http://www.dansdata.com/diyups.htm for a good description and a list of advantages. Mine comprises a Powertech MP3090 regulated 3-15V power supply connected to a 54 Ah AGM battery and a 300w pure sine wave inverter (connected in parallel). This gives me a clean, realiable 240V supply for all my equipment. I use a laptop in the obs but that's it's own UPS, so I run it directly from mains.
The power supply I have is quite beefy - a 40A model - much more than I need (25A peak). I only bought this because Jaycar gave me the display model cheap as they had no other decent smaller models left. I already had a 300W pure sine wave inverter (a camping accessory!). The battery was relatively cheap. Deep cycle AGMs around the 50-70Ah range are usually quite expensive - $300 to $400 but this one, an Ultimate UL-60, was only $250 and I'm expecting to get a good 5 years life out of it. Since I'm manually charging the battery (ie without an intelligent charger) I thought it would be wise not to spend too much in case I bugger it up! Most of the time though it will be on a float charge.
Now I'm totally immune to power failures and fluctuations and I'm told surges & spikes as well. In the event of a blackout my system will continue running happily from the battery for about 4 hours (without any switching hiccups during the cutover that you might get from a line interactive or standby UPS). That's enough to finish a nights imaging! Note that if you run a PC in your obs you'll need a beefier inverter and, depending on how long you want to continue operating, maybe a beefier battery.
You might think it expensive (around $700 to buy all new components with a smaller power supply) but that compares favourably to the cost of the cheapest (and decent!) online commercial UPSs (between $500-600) which will usually only give minutes of up time! In any case, for peace of mind and uninterrupted imaging when you live in an area with substandard mains reliability, it's pretty good value!
Cheers, Marcus
