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 | generalThe 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.
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 directly to a suitable
power inverter in turn connected to the renewable system
battery bank. (See our article
Dual Powered Lighting Circuit).
However, is not an optimal solution since
manual intervention is required when the batteries become discharged. Ideally 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.
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 simply stops supplying power (sometimes sounding an alarm/buzzer at the same time). Using this information we can put together a simple
automatic mains/inverter switch using just a
230VAC DPDT Relay.
A
DPDT relay (pictured above) has eight connections - two for the
coil which should be connected to the live and neutral outputs from the power inverter, two
NO's, two
NC's, and two
COM's. When the relay is energised (i.e. when there is 230VAC across the coil from the inverter), NO1 is connected to COM1 and NO2 is connected to COM2. When the relay is not energised (when the power inverter is not putting 230VAC across the coil), NC1 is connected to COM1 and NC2 is connected to COM2.
Therefore, connecting the relay up as shown in the schematic diagram above (and the connection list below), the lighting circuit will be powered by the
inverter when it is on, and the rest of the time by mains
electricity. The switchover occurs in the fractions of a second.
Connections:
Inverter Live to Relay Coil
Inverter Neutral to Relay Coil
Relay COM1 to Lighting Circuit Live
Relay COM2 to Lighting Circuit Neutral
Mains Live to Relay NC1
Mains Neutral to Relay NC2
Inverter Live to Relay NO1
Inverter Neutral to Relay NO2
Buy a DPDT Power Relay
The
relay pictured in this article is available for around £2 plus £1 for the socket from
Rapid, for around £4 from
Maplin, or from £0.99 from this search on eBay UK:
DPDT Relay.
Safety
DISCLAIMER - mains electricity can KILL. We recommend that you talk to a qualified electrician before attempting to implement any of the ideas discussed in this article.
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: 14:16, 19th Aug 2008Comment on this Article
If you have any comments on this article, please email them to
neil@reuk.co.uk.
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