Inverters

You may see Inverter output rated in VA (VoltAmps) rather than Watts and for many appliances this will equate to the number of Watts, but for those appliances with motors in them, the VA needed can be up to 50% more than the Watts needed.

Peak (or surge) describes the output deliverable for several seconds - the Inverter components won't blow up at that amount of load, but they will heat up quickly. Continuous ratings are usually limited by the heat that needs to be removed when running continuously. Ideally you would find out the Peak and the Instantaneous ratings of your appliances and check that they were less than the Inverter output, but you can't rely on this because most appliances don't state the start-up or peak power - and the length of the peak really needs to be known too. Unfortunately, the only way to be sure, is to test the appliance with the Inverter!

Modified Square Wave (MSW) Inverter

Most appliances will work from these basic Inverters, but unfortunately unless you can look at the internal electronic design of the appliance, you can’t be sure if you will really need a Sinewave Inverter. The squarish waveshape can also confuse the timing circuits in some appliances that use the Mains Frequency to control a clock. If the appliance doesn’t work normally or makes unusual noises, then disconnect it or you may have expensive damage. These Inverters also generate more interference to TV and AM and HF radio reception than Sinewave Inverters and can cause buzzing in CD players.

Sine Wave Inverter

Sinewave Inverters are more expensive than Modified Square Wave (up to twice as much) because more components are needed to electronically generate the Sinewave. You may consider that If the appliance has a Transformer or an Induction Motor (refrigerators and non-Inverter Air-conditioners), then it most probably needs a Sinewave Inverter to prevent overheating. Now this is not necessarily true, since fridges and freezers can work fine off Modified Sine wave inverters, and in fact - you wouldn't really notice any difference powering a Fridge from a Modified Sine Wave Inverter to a Pure sine wave inverter. Also, if an appliance has "Modern" speed controls, it is not really recommended for use on any type of Inverters as the constant varying Power from the Inverter to the appliance can damage both sorts of Inverters. Computers are normally fine as they have Power Pack's specifically made to limit fluctuations.

Isolated Output

If you are using only double-insulated appliances (i.e. they have no third Earth-pin on the Mains plug) with your Inverter, then it doesn’t matter if the Inverter has total electrical isolation between the DC input and AC Output (provided there is no fault to earth). In larger installations with an earthed neutral, or if you have earthed appliances such as Washing Machines, then if the Inverter is not isolated, the DC input will be up to 120 volts AC above the Mains Earth - a very dangerous situation!

Soft-start

Some loads draw much more current when starting up compared with steady operation e.g. a Halogen bulb draws ten times its normal current when first turned on, and motors can also draw very high currents as they come up to operating speed. To reduce these massive current surges, some Inverters bring the output voltage up to 240 volts progressively over many seconds. This means you will be able to use an Inverter with a smaller continuous power rating, for a particular load.

Low Voltage cut-out

To prevent damage to your battery, it’s important that the Inverter switch itself off and remove all current drain, when the battery voltage drops below a set limit. It helps if the cut-off voltage can be set by the user, based on the type of battery, the depth of discharge desired and the voltage drop in the wiring. Keep in mind that as battery voltage drops, the Inverter will draw more current to keep input power constant, so this means that voltage will drop fairly quickly towards the end, and therefore manual monitoring of battery voltage is not really practical.

Automatic Fan Cooling

To get rid of waste heat in Inverters over 200 watts, it really helps to have an internal fan and usually these are automatically switched on only when needed, to minimise power used.

Earth leakage protection

Bigger Inverters may have these built-in, but they can be easily added.

Meters

You can get by without voltage and current meters, but with them it’s easier to check if your system and appliances are healthy, or if you’re close to overloading your Inverter.

Autostart

Some larger Inverters automatically sense when any appliance is connected or switched on, so that the Inverter only draws significant power when it’s actually needed. This is particularly useful in large vans, mobile homes or fixed buildings, because you don’t have to switch the Inverter off and on when using appliances.

These days, manufacturers don’t always include an Austostart feature - especially when it comes to Pure Sine wave inverters, since they will typically have a remote.

Remote Control

For installations in large vans, mobile homes or fixed buildings, it’s handy to be able to control it remotely, because the Inverter may be mounted in a cabinet near the batteries.

Inverter/Charger

For permanent Installations, the Inverter may be able to charge the batteries when mains is available, but there is no solar power available.

Grid-Feed Inverter

For permanent installations, when there is surplus solar power available, the Inverter can feed power back into the 240volt mains, resulting in electricity being ‘sold’ to the electricity company.

Overload cut-out

Not really optional, but the more sophisticated ones will protect against over-temperature as well as over-current, over-voltage or under-voltage (that can damage some appliances).