Backup power solutions - Selecting an Inverter/UPS for your home/office.
Nobody wants to be without lights, TV, internet, computer or mobile communication when the power goes out. We also don't want our security system to shut down during a prolonged power outage. These appliances have relatively low power consumption, so an inverter/UPS (Uninterruptable Power Supply) can be used to keep them powered during a blackout. Before choosing an inverter/UPS, take a quick read through this article which should help you make a more informed choice.
What is an inverter?
An inverter is a device used to convert DC battery power to 230V AC mains power. Usually this will be from a 12 or 24 Volt deep cycle battery or bank of batteries, specially designed for use in backup power solutions.
Inverters are available with output power ratings from as little as 100 Watts to tens of thousands of Watts. Typical home inverters are rated from 500W upwards. When the inverter is made to automatically start providing power when the mains power fails, this is referred to as a UPS as the appliances continue working without interruption.
Inverter Power Rating
The inverter you choose will depend on the power in watts (or current in Amps) of the appliances/equipment you want to run. You can check this by looking at the product specification label or in the manual of your appliances. You need to know both the continuous rating in watts or amps and the peak/surge rating in watts or amps. Without this information any further calculation is not possible.
Continuous vs Peak or Surge Power
Some appliances such as fridges, air conditioners and electric motors require very high current to start, which is referred to as "inrush current" or "surge power". This needs to be factored in when deciding on which inverter to use. The surge power required for these appliances can be as high as 7 or 8 times the continuous current required when they are running.
Inverters are rated in continuous power and peak/surge power. Continuous power is the total power the inverter can deliver continuously while peak/surge power is the amount of power that the inverter can deliver for a brief period, usually when the equipment/appliance starts up. Most low-cost inverters are not designed for loads with a high start-up current.
Items such as TV's, modems, routers, LED lamps, computers and cellphone chargers require very little additional power when they are switched on, so we can use the actual power rating on the device to calculate total power of the inverter.
Pure Sinewave vs. Modified Sinewave Inverters
The power supplied by Eskom is a pure sinewave, and all electrical appliances are designed to work efficiently on this power supply. A pure sinewave inverter is therefore the ideal choice to ensure that appliances are able to run without interference or overheating.
Modified sinewave inverters recreate the sine wave electronically and therefore the sine wave isn't perfect or pure, which can cause some appliances to malfunction. These are some of the appliances that may experience problems when powered from a modified sinewave inverter :
Batteries are critical components of any backup power solution. Batteries used for backup power solutions are different to regular batteries used in your car, as they have a different charge/discharge cycle profile. Vehicle start batteries should not be discharged below 90% of their full charge. Marine/solar deep cycle batteries can be discharged to around 50% of their full charge before their lifespan starts to suffer.
Increasing the number of batteries will increase the length of time your backup power solution can provide power, however this will push up the cost of the backup solution.