"Ian Stirling" wrote in message
...
Bill Stock wrote:
I had another power outage last weekend (4+ hours), so I finally broke
down
and bought a couple of refurbed UPSs. They should last a while as they
are
36 amp hours each. The Goldfish tank only uses 24 watts (2 Fluval 304s),
as
I won't connect the heater or lights. But I was wondering about the
Tropical
tank, since batteries last exponentially longer under reduced load. Would
I
not be better to have one 100 watt heater running twice as long, rather
than
the normal two 100 watt heaters. In fact I was thinking about replacing
the
two 100 watt heaters with a decent digital heater and leaving one of the
100
watt heaters in the tank as a backup. I would set the backup below the
threshold of the main heater (say 75?F) and connect it to the UPS. This
way
the heater would not come on until the power had been off for a while.

100, 200, or 400W heaters will use the same amount of energy at the same
temperature, if they can maintain the temperature at all.
100 gallons of water maintains its temperature for a long while, and most
fish are fairly tolerant if it's once.

Not arguing that 100 @ twice the time period is the same as 200 @ one time
unit. But if you look at the run time chart for most UPS you will see that
the last MUCH longer at smaller loads, i.e. not a linear increase. For
example my UPS lasts 8 minutes at 900 watts and 301 minutes at 50 watts. But
900/50*8 =144 NOT 301. I actually ran a test on the weekend @ 25 watts and I
got 8.5 hours out of the existing batteries, which are only holding about an
80% charge.

I would not have used UPSs, they arn't really the right tool, for small
loads,
as the battery is sized to discharge through the inverter in some half an
hour, but the inverter will typically use 5%-10% of its nameplate power as
parasitic power.
So, with a 600W UPS, you may be looking at 80W draw from the battery,
rather than 30W, which you might get with a small inverter.

I looked at the Inverter/Battery setup, but many of the inverters put out
POOR waveforms, which are detrimental to many powerheads. The UPS I bought
has a fairly good reputation for a 'cleaner' sinewave. Although I may still
go this route for powering up the fridge/freezer for longer blackouts.

I'd have gone with a deep-discharge rated battery, and a small inverter,
combined with a small battery charger to keep it charged.

Not to say it won't work of course.
A tip, you may well find that you get better run-time if you daisychain
the
UPSs, rather than having both powering seperate stuff.