The post shows how to configure a simple LED relay changeover emergency light circuit using a battery back up which gets charged during mains presence and changes over to LED/battery mode as soon as mains fails. The idea was requested by one of the members of this blog.

Discussing a Circuit Idea

The following discussion explains the application details for the proposed LED relay changeover emergency lamp circuit

I am trying to make very simple changeover circuit.. where I am using a 12-0-12 Transformer to charge a 12v Motorcycle battery via mains.. when the mains go off the battery will power a 10w LED. But, the problem is the relay is not switching off, when the mains goes down.. Any ideas. Want to keep it really simple.. 12VDC Relay / 2200uf-50v cap on Transformer.

Hi, make sure that the relay coil is connected with the rectified DC from the 12-0-12 transformer. The relay contacts should be only wired with the battery and the LED

Hi Swag,

Firstly Thanks for the Reply.

1. Yes the Relay Coil is connected with the Rectified DC.

2. If I connect the relay contacts to Battery / LED only, then how will the Battery get charged when Mains is ON?
If i am not missing anything..

The Design



The above circuit is self explanatory and shows the configuration for implementing a simple LED relay changeover emergency lamp circuit.

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