determining power use
Batteries are rated for amphre hours, i.e., the number of hours of cold cranking time. A car battery for example would be about 60 amp hrs, a scrubber battery or golf cart battery (deep cycle) is normally in the 105 amp range.
Lots of people on long range sailboats use deep cycle batteries to power their entire electrical system via inverters, most use large industrial equipment batteries like those for golf carts, floor scrubbers, etc. They withstand the constant charge and discharge cycles better than a standard car battery. in the US they costs about 75-100$ each but put four in series you get some 400 amp hours of use, 8 = 800 amp hours.
A car type battery will not withstand the deep discharges and will eventually stop taking or holding a charge. Meaning you can power up a battery charger to max amps and zap a "bad" battery for hours and find the battery wont accept or hold the charge.
SO, what does all this mean in regarding to power use on the inverter?
Read below:
Now, each electrical device plate usually shows watts/ hr used, i.e. the 100 watt light bulb or the 600 watt (color tv).
Battery power is stored in units of current = AMPS
Current (amps) = watts / volts
a 100 watt light bulb on 110v power is 100 W / 110 V = 0.90 amp/hr used
a 100 watt light bulb on 12v power is 100 W / 12 V = 8.33 amp/hr used
So, from this you can see two things. It takes a lot more current / ampherage to power 100 watts via a 12 volt circuit (your inverter system) than it does a 110 volt circuit (wall power).
So, when your devices are powered by the inverter at 12volts you are using at least 8 times more power (amps) than when your using the same device via 110volts. And subsequently it will take longer to recharge those lost amps when the power comes back on.
So, using the above formula you can check each device plugged into your inverter to determine the minimun amps draw on the inverter.
A TV, two - three 100 watt bulbs, a fan going - would probably range somewhere in the 1000-1200 watt / hour range i would guess.
Therefore, 1000 watts / 12 volts = 83 amp hours.
Your battery bank is probably in the range of 400 amp hours if your lucky. So it would take only 4.8 hours to totally drain your batteries to a less than readable voltage.
The moral of the story - if your on your inverter and you have essentialls like lights and fans, etc...turn off the high wattage stuff like TV's, DVD's, Refrigerators especially, A/C's.
Good luck, things I learned while living on a sailboat and using everything on 12volt system. Of course I could recharge my system with wind and solar power every day.
Karlheinz
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