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!
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
may have these built-in, but they can be easily added.
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.
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.
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.
For permanent Installations, the Inverter may be able to charge the batteries when mains is available, but there is no solar power
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.
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).