For lead-acid rechargeable batteries, the best bang for the buck is the 'deep cycle marine battery'. These have special construction which keeps them in a usable, rechargeable state longer even if abused. These are more durable than 12V car batteries, but about the same cost.
Lead-acid batteries release the flammable gas, hydrogen, into the atmosphere when charging. This is normally not an issue as long as the space is not completely airtight. A battery is usually perfectly safe in the home, since the tiny amount of very light hydrogen quickly passes up and out of the building through the smallest of crevices. Nonetheless, be aware of the hazard.
Batteries should be kept in a charged state at all times. Leaving the
battery discharged for any time can shorten its life. Any time your 12V
battery drops to 11.9V, it's time to charge it or lose it! Battery care
is something of a mystic art -the internet will have alot more info than
can be written here.
Interstate Batteries
Concorde Batteries
Gasoline
Older (such as 10-20 years old) gasoline generators consume about 0.3 gallon of gasoline per 1000 watts (1 KW) per hour. If you are going to buy an older unit, try to find an 1800 RPM generator. these putt along at a low speed and are characterized by a relatively large engine, and are built to run for extended periods of time, such as 24-36 hours.
Modern ones such as a Honda, etc., can consume much less, on the order of 0.2 gal. per hour per KW, due to both advances and compromises in design. These are fine for intermittent use, but they are loud, and operate at 3600 RPM. Because of the high speed, they wear quickly if used for extended periods.
"Contractor" type portable units are made for 8-12 hours continuous use at a time. You can use these for extended periods, but they are loud, run at 3600 RPM, and will wear more quickly than an industrial unit. Also beware that some of these use a system by which the engine idles slowly until a load is applied. This can wreak havoc with electronics equipment since the voltage and frequency change radically when this happens. These generators are made for operating lights and power tools, not computers, radios, and air conditioning gear.
Most smaller gasoline generators require the oil to be changed every 24 hours. This is due to the small oil capacity and the 'splash' oiling system. There is no oil pump, the oil is splashed on the moving parts by the crankshaft rotation.
Larger and more expensive units, such as those designed for use in motor homes, have a larger oil capacity, a pressure lubrication system (oil pump), and a filter. This is the best type, and can be found used at wrecking yards where old Winnebagos go to die. Finding one that has the pressure oiling system and runs at 1800 RPM is your best bet.
Maintenance of Gasoline Generators:
For proper maintenance, they must be started every month, and run for at
least 15 minutes to evaporate any moisture in the system (crankcase,
muffler, etc.), and then (if you are going to do it 'by the book') the fuel
supply shut off to let the carburetor bowl run dry and prevent varnish.
Even an old used one is reliable if taken care of. My $250 Kohler 3.5CM21 is 30 years old still works well. I am certain that I can go right now and fire it up, because it is well cared-for.
There are many manufacturers of gasoline generator sets, and the price generally reflects the quality. Here is a short list to start with.
Cummins/Onan
Kohler
Honda
Diesel Generators
Diesel generators come in mostly larger sizes of 8KW and up, and are much more desirable than gasoline types, and far more rugged. Typical consumption is 1/2 of the fuel, and a typical 8KW model uses only 0.08 gallons per KW per hour. That's 0.64 gallons per hour at 8KW! They are designed for long term use and most come standard with pressurized oiling, water cooling, automatic shutdown, etc. These are the true "Cadillacs" of the generator family and the price reflects it. One very reliable yet inexpensive brand of Diesel generator comes from China Diesel.
Maintenance on a Diesel engine would include draining the fuel bowl/filter if equipped with a drain cock, to prevent water from building up and entering the injector system. This is done on truck engines after the vehicle has sat unused for a while. On a military vehicle such as the M35 2.5 ton truck, this is done before and after each use, if the truck has not been used for a week.
Diesel fuel is very hygroscopic (absorbs water easily), and this is the worst enemy of a diesel engine. A Diesel is a special item, and the reccommendation is to not only follow strictly the instructions in the manual, but also to get -and read- a good book on the care and service of diesel engines.
Other information and diesel generators of all sizes and costs can be found on the WWW at places like these:
industrialdiesel.net
Stauffer Diesel
All World DieselCheck out the FAQ!
Or just do this pre-defined search for hundreds of links.
Note that most all UPS must be first presented with AC power before they will be able to failover to batteries, even if the cells are full!
The issue here is that if you suddenly find yourself on emergency power, and you wish to conserve the battery charge, a problem exists that if you switch off the UPS, you can't turn it back on. This can be overcome in many cases by a modification.
An improvement technique involves using deep-cycle marine batteries external to the UPS itself. This works for any UPS and gives far more watt-hour capacity than those little UPS batteries. The power is supplied to your load for 4-6 times longer. The marine batteries cost about the same or less than as the originals, beleive it or not.
This creates an economy, as 'dead batery' UPS's are almost free, and most in the 500-1000 watt range use only two 12V batteries. (smaller ones use just one battery, and larger ones may use 4 or more)
Lead-acid batteries may be kept in a large plastic tub such as found at wal-mart, safely keeping them off the carpet.
Many might object to having more weight in batteries than in the UPS itself, but if you enter most corporate telephone rooms you will find a very large rack of batteries, much larger than the phone switch's power unit or UPS. They are interested in system availability.
Another note is that UPS's take about a day to fully charge the batteries, maybe more with the big batteries. The (trickle) charge rate varies with the UPS. If you have a generator, a good battery charger is a fine idea, to charge the UPS batteries while on generator power.
How big a UPS? It depends on what you want to run. A computer or TV will stay up on a 250 watt unit, but the power surge of turning on such a load 'cold' might cause the small UPS to shut down. A 1000 watt one won't care, it'll stay up. Just don't turn off your gear till you are ready if your UPS is of low wattage. Megalomaniacs -get a 500-1000 watt unit!
For more info, APC's website is a good place to have a first look.
Inverters may always be started from the battery, an advantage.
There are two types of comercial inverter designs.
The first kind has a small power supply (trickle charge) for the battery charger and a large inverter circuit for supplying AC power. The inverter only runs when the AC fails. -like a UPS.
The second kind has a large rectifier which actually converts the incoming AC power to the DC battery voltage, and then an inverter which runs from this power supply voltage at all times and supplies all power to the load. The battery 'floats' on the power supply DC voltage, staying charged, and when the incoming AC power fails, there is no glitch as the battery is hardwired right there online to the inverter. These are about twice the weight and more expensive than the first type of comercial inverter, but also usually fast-charge the battery upon restoration of AC power.
Some special inverters also match the incoming home AC power waveform, so that you can generate power from the wind and offset your electric bill to a degree. Here are a couple places to look:
Tripp Lite
Trace
Astron (makes power supplies too)
Check out these manufacturers' pages for technical information:
Siemens
Trony
Canrom
Solar Solutions
Shop wisely -prices for the same consumer unit or rated power level vary greatly between dealers! Search out the original component manufacturers (such as Siemens) pages first.
Finally, here's an online magazine devoted to emergency/alternative power:
Homepower
Just my 2 cents, based on using and hacking this kind of hardware. If anyone has comments or questions about these topics, please ask the webmaster.
CPL Jankowiak