Inverters and what to look for:.... this could be getting too far off topic, I guess someone will tell me if so....
All inverters work the same. The input DC battery voltage, 12/24 volts is converted to high frequency AC, stepped up to 300 volts,rectified back to DC, then chopped into a 50 or 60 cycle 240 volt regulated AC waveform to power mains appliances.
The important features of any inverter is the following, in order of importance.
Overload protection. The better this is. the more reliable the inverter will be. This ability to adequately protect itself is severely lacking in cheap inverters. The easy answer here is to under rate the inverter to guarantee it never approaches over half of its claimed rated output. Pretty much all cheaper domestic type inverters are grossly misrepresented in what current they can realistically supply. Simply put, the manufacturers lie. A 1000 watt inverter can be safely rated at 500 watts continuous. Ignore any grandious claims of surge capabilty, this is largely BS. See here for a scary rundown of a really bad design.
http://ludens.cl/Electron/chinverter/chinverter.htmlUndervoltage switchoff. Generally all cheap inverters will automatically shut down when input battery voltage drops below a preset level.. This is important to prevent the inverter drawing excess current in an attempt to supply the load as the battery voltage drops. Check this before buying.
Waveform. All cheap inverters use whats called a modified sine wave. This should really be called a modified square wave. These cause severe radio and TV interference, and excess heating of some electric motors. These are fine for lighting circuits, and the use of small power tools, drills, grinders etc. For refrigeration, pumps, washing machines and any induction type electric motor that will run for longer than around 15 minutes, use a more expensive true sinewave inverter just for these appliances. Pretty much all electronics are tolerant of modified sine inverters, as they use internal switch mode power supplies that work in an identical fashion. If radio interference is a problem, additional filtering can be attached on the outputs of each noisy inverter.
Stand by current. To have instant power on demand, all inverters must be powered continuosly, and therfore each will put a constant power drain on the battery bank, and this quickly adds up. Many cheap inverters will not mention this drain in the spec sheet. Avoid these. A good figure to look for is .3 to .5 amps standby. This could also be written as 300 to 500 milliamp or mA. The lower this figure is, the better the inverter is likely to be. Some inverters will "pulse" the line every second to see if a load has been switched on, and if so, will "wake up" and run until the load is disconnected again before reverting to sleep mode. These types have very low standby current, but likely more expensive.
Many other protection circuits may or may not be incorporated, such as over temperature, overvoltage etc. These are not so important if the inverter is used well below maximum ratings. Manufacturers that try to make a cheaper product will leave everything out that they can that does not directly or visibly affect the normal operation of the device. Even many name brand inverters contain generic Chinese internals that are unlikely to be superior except in price.
Reverse polarity protection. Ignore this one. Not important at all. If you need this to work, you have no business messing with this stuff and are likely a hazard to yourself and others.
Fuse the positive input lead to the inverter with a rating twice what current is expected. This fuse will protect the wiring when the inverter eventually dies, sometimes very spectacularly, with smoke and flames.. fuses here can be rated at 100s of amps for the larger setups, welding cable is useful source for high current DC runs.
Seperately fuse the mains output of the inverter to whatever current maximum you have allowed for that specific inverter. This will help protect the inverter from any overload that its internal circuits probably cannot handle. Accidental overloads will happen!! Fuse ratings here will generally below 10 amps. Remember, amps = watts divided by volts. This information is always labeled on each appliance you intend to use.. Induction motors in general can require 5 to 10 times their running current when starting. Most inverters will attempt to supply this without failing, some wont, depending on the imagined surge current specs the advertising people have invented. Here, the only way is to try it unfortunately.. we are running blind, and trusting the manufacturer on this one.. Large industrial circuit breakers can also be used here on a lower voltage , despite being mains rated if these can be got cheaply. A 24 volt inverter supplying a 2400 watt 240 volt load, such as a two bar electric heater, is using 100 amps from a 24 volt battery bank, or 200 amps from a 12 volt battery bank.... these are very very large current demands.
By all means spend more on "better" inverters, but, trust me..... they will eventually go up in smoke too, in my experience their is little benefit in doing this. A run of the mill Chinese inverter will last usually 1 to 3 years possibly longer if the above steps are taken. An expensive one will last around the same time , but can be run harder.... much closer to its advertised ratings.
Once every six months, clean any crap out of any cooling slots, check the fans, power down and in damp climates, squirt copius quantites of a CRC5/56 or a similar product into the internals to prevent corrosion and moisture . After a few minutes, its safe to power them back up. Just squirt into any cooling slots or openings and let it drain. Dont do this in hot dusty climates.
Run seperate circuits for large appliances, lighting, wall outlets and workshop. These all terminate into the engine shed with mains plugs that can be alternated into any inverter for fault finding or hot swapping in case of failure. Unfortunately, some electrical wiring codes in nearly all countries must be substantially ignored in order to make a practical off grid system.... but use grounding wherever possible. Also think of safety..... its a bugger being electrocuted even once, so no live exposed terminals. My experience indicates pretty much all registered sparkies have very little to no working knowlege of off grid systems, in this country at least, and if consulted you will end up with a very expensive white elephant... it will be legal, but it wont work properly.
