Free running inverters - Converting battery energy to mains electricity

Stand alone or free-running inverters are used to convert energy stored in a battery to mains energy. This would typically meet the situation caused by load shedding when mains power from the municipality is disconnected for periods.
The energy generated is used to power selected devices such as lights, computers, modems and entertainment devices.

The free-running inverter is used in a similar situation to that of an external diesel generator to keep certain selected services running when load shedding is in force. The running costs of a battery/inverter system is much less than getting similar energy from a diesel generator, but the amount of energy available from the battery is far less than one can get from a diesel generator.

The devices that are going to be powered by the inverter are on a seperate plug system to the rest of the home.The inverter might have a feature that mains power can bypass the inverter to feed those plugs when there is an electricity supply, which supply controls a switch which changes to the inverter output as soon as the mains fails.

1500watt 12vDC to mains inverter

1500watt 12vDC to mains inverter

Depending on the sophistication of the charger, you will get different features. Some monitor the battery voltage and provide alarms if the battery voltage drops too low or gets too high if it is overcharged. If the alarms are ignored the inverter switches off to save the batteries. The inverter will also switch off if the load being drawn exceeds the capacity of the inverter, such as might happen if you plug a kettle into its output sockets.

Another feature between expensive inverters and simple inverters is the quality of the output mains signal. In the simple ones you are getting a fifty hertz square wave while the more expensive ones have simulator sine wave outputs. Some devices that are using the inverter generated signal might be sensitive to the purity of the output signal - such as cameras. Although some manufacturers claim pure sine wave output, this is a marketing plug that is not true as the only way to make a pure sine wave is with a physically large filter which is very heavy and expensive.

Charging the battery
Energy needs to be added to the battery periodically. Usually this will be from a charger that is connected to the mains, so that as soon as the mains supply is restored, the battery can be recharged ready for the next outage.
Users might choose to charge the battery from solar panels.
This requires that the charger voltage be reduced to a voltage suitable for battery charging and then charge the battery. For those using Lithium battery packs this would typically be 52 volts while the solatr panels might typically be delivering 150 to 250 volts. This reduction is done in a MPPT charger that optimises the energy conversion from the panels and controls the charging of the battery.

In smaller 12 volt systems that a typical home owner would use, you get a solar charger that you connect directly to 12 volt or 24 volt panels and the charger transfers the energy to the battery ensuring it is not overcharged.

No-break inverter system
For those devices that do not want any break in the incoming supply, such as might occur when the mains drops out and the inverter starts - you can setup a no-break inverter supply. The devices you use on this supply might be sensitive computer equipment.You will have a dedicated plug from this inverter to the critical devices.

Here you have a dedicated inverter and battery that is operating continuously and its battery is being kept charged via a mains charger. The battery capacity is large enough to outlast the longest expected outage.

Getting help and advice
This description is provided to show how easy it is to get going. I am not selling anything, just encouraging users to take the first step. You can contact me for help and advice from Mike at Tel +27 72 992 6040

17 April 2023

Also see an article on Low cost solar solution
Also see an article on Design of computer controlled solar system for smart home
Also see an article on Solar water heating - solar geysers
Also see an article on Measuring systems for solar systems
Also see an article on Gridtie inverters -Converting solar energy
Also see an article on Battery storage systems
Also see an article on Energy equivalents