| RSS Web Feed for Renewable Energy UK | REUK Shop | Bookmark Site | About Us  

Switch from Inverter to Mains Automatically



Switch From Inverter To Mains Automatically

Power a circuit directly from a power inverter, but with automatic mains power back up.

electric circuit | storage | general
Printer Friendly Version Print Article     

The majority of domestic renewable energy is generated to supplement an existing mains power supply - for example, an array of solar panels used to reduce the costs of powering a home.

Sunny Boy Grid Tied Inverter

Unfortunately the cost of grid tie inverters with UK G83 approval (and professional installation) puts them well outside the price range of most small to medium microgenerators. Therefore, if a microgenerator with let's say one 150 Watt solar panel and battery backup wants to power a lighting circuit in their home, they will need to look for alternative means to achieve their goal.

One way would be to separate the chosen lighting circuit completely from the mains power supply, connecting it direclty to a suitable power inverter in turn connected to the renewable system battery bank. However, this would not be a very good solution since the lights cannot be used when the batteries are discharged. We need a way to power the lighting circuit from the renewable source, but with an automatic way of switching back to mains power when necessary.

DISCLAIMER - 240 Volt AC electricity can KILL. We recommend that you talk to a qualified electrician before attempting to implement any of the ideas discussed in this article.

Using a Relay to Switch from Inverter to Mains Power

All power inverters have an automatic shut off function which prevents the attached battery bank from being overly discharged. When the voltage of the batteries falls to a certain fixed level, the inverter will stop supplying power. Using this information we can put together a simple automatic mains/inverter switch using just a 240V AC Relay.
240 Volt AC relay rated at currents of up to 25 Amps

The relay has three connections, Common, NO, and NC. The live wire from the lighting circuit is connected to the Common, the live wire from the mains supply to NC, and the live output from the power inverter to NO. The live and neutral outputs from the power inverter are then connected across the relay coil. This is all shown in the schematic diagram below:

Use a 240VAC relay to switch between inverter and mains electricity.

When the power inverter is switched on and the batteries are charged, the relay coil has 240VAC current flowing through it. This moves the contact within the relay from the NC to the NO position connecting the live wire from the inverter to the live of the lighting circuit - lights are powered from renewable energy. When the batteries are discharged, or if the inverter is switched off, the lighting circuit live will be connected to the live of the mains supply via the NC of the relay - lights are powered by mains electricity.

This is a fully automatic system with switching from inverter to mains power in a fraction of a second.

To make it safe, a circuit breaker should be used (rated the same as the mains circuit breaker for this circuit), and a manual ON/OFF switch and LED indicator included to enable the user to see which power source is being used and manually switch to mains power if desired.

Further details on the implentation of this scheme have not been included since if you do not know how to do it, you really should not be doing it!

Article Last Modified: 16:55, 4th Sep 2007


Recommended Related Articles

People who read this article also enjoyed the following articles:

DIY 2kW Wind Turbine
Read about a home built 2kW wind turbine constructed from scrap
Article Last Modified: 08:46, 4th Oct 2007
wind | recycling

Power Inverters
Find out about the uses of power inverters in renewable energy generation
Article Last Modified: 16:48, 6th Dec 2007
storage | general | electronics

Permanent Magnet Generator
Build a wind or water power system with around a PM Generator
Article Last Modified: 17:33, 2nd Jan 2008
wind | hydro

Interconnecting Batteries for Battery Bank
Find out how best to connect batteries together into a battery bank
Article Last Modified: 13:53, 23rd Feb 2007
storage

How I Built A Wind Turbine
Read how a wind turbine was built for under US$150
Article Last Modified: 10:24, 6th Jan 2007
wind | education

Relays and Renewable Energy
Find out more about relays and their uses in renewable energy applications
Article Last Modified: 16:52, 2nd Aug 2007
electric circuit | electronics | general

Make a Simple Battery Status Monitor
Monitor battery status with this easy electric circuit project - no skill required!
Article Last Modified: 12:33, 16th Mar 2007
storage | electric circuit

MiniWind Wind Turbines
Find out more about the MiniWind range of wind turbines and purchase products with an REUK exclusive 10% discount
Article Last Modified: 17:33, 2nd Jan 2008
wind | shopping

PVC Wind Turbine Blades
Learn how to make your own PVC wind turbine blades
Article Last Modified: 11:59, 24th Jan 2007
wind

Grid Tie Inverters
Find out more about Grid Tie Inverters - connect your RE system to the grid
Article Last Modified: 16:36, 2nd Jan 2007
general | wind | solar | electronics

© 2006-2008 REUK - All Rights Reserved
Page Last Updated on 22nd May 2008 at 10:50:15am

Latest
Articles


Wind Turbine Axial Flux Alternators
Learn more about the design of an axial flux alternator - used in wind turbines and hyrdo power
wind
09:27, 7th May 2008

Solar Water Heating Pumping Station
Find out more about the new solar water heating Pumping Station
solar
11:53, 6th May 2008

Moonlight Night Light Product Review
A review of the Moonlight Night Light
shopping
14:00, 30th Apr 2008

P3 Kill a Watt PS P4320
Find out more about the Kill-a-Watt Power Strip P4320
energy efficiency
13:20, 30th Apr 2008

Calculation of Wind Power
Calculate the power of the wind hitting your wind turbine generator
wind
15:06, 18th Apr 2008

Renewable Obligation Certificates
Generate renewable source electricity and get paid twice with ROCs
general
11:37, 15th Apr 2008

Jobs in Renewable Energy
Find a job in renewable energy and green technologies
general
12:16, 8th Apr 2008

Rainwater Toilet Flush System
Find out how to put together a complete rainwater fed toilet flushing system
water
10:50, 5th Apr 2008



REUK Shop

Popular Items


KILL A WATT
Plug in Mains Power and Energy Monitor
£19.99 each.
Energy Saving



EFERGY HOMECO2METER
efergy homeCO2meter wireless electricity monitor
£38.99 each.
Energy Saving



240V LED SPOTLIGHT BULB
240V LED GU10 bulb. 20 x 20,000mcd white LED 1 Watt bulb
£4.99 each.
Energy Efficient Lighting



RAINWATER DIVERTER KIT
Rainwater diverter kit for standard plastic 65mm square and 68mm round downpipes
£8.99 each.
Water Conservation



300 WATT POWER INVERTER
Convert 12V DC battery power into 230 AC to power portable televisions, computers, video recorders etc. 300 Watt power rating - peak power 600 Watts
£29.99 each.
Renewable Energy System Parts



12 VOLT 3 WATT SOLAR PANEL
Waterproof 12 Volt 3 Watt Solar Panel - 199 x 136mm with fitted leads (fiberglass and resin).
£19.99 each.
Solar Power



SUNGUARD SOLAR CONTROLLER
4.5 Amp at 12 Volt solar charge controller - fully encapsulated and weatherproofed
£22.79 each.
Solar Controllers