Well that's 2.5 hours at a 250w draw. To be comparable to the Vortech example, I could run a single Tunze 6100 at 1/2 power (22.5 watts) and extend this to about 28 hours. I assumed that running a return pump from my 100g sump would help oxygenate the water better then a powerhead would, and increase the volume of water and thereby conserve more heat longer.
This box can be powered by my car as well so I could get an extension cord and do the same as you. I can also purchase another deep cycle battery for another $120 and almost double that time, much like you could do with your inverter.
I agree that 2.5 hours is a short time to be out of power and if I knew that it would never exceed that length of time I'd go without a backup. But if I assume that 5 hours is the max for my part of the country then I've cut that in half and now I've only got 2.5 hours of 0 power, which as you said isn't much. Basically I was using 250w as a maximum power draw when I was choosing options for a backup.
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225g reef 3x250w MH 8x39w T5 Sfiligoi/ACLS, Deltec AP851, Deltec PF601S, Deltec KM500, Ozotech Poseidon, Aquatronica, Tunze TS48, Tunze Nanostream 6025s, Aqua UV 114w, MTC Ozone reactor, Cole Parmer peristaltic pump
67g reef, Euro-Reef RS135, 60g refugium, Mag 9 return, Tunze Nanostream 6025s, 4x39w T5
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