This video is about :
how to prevent modem shut down and lose the internet connection of surveillance camera, during losing AC power,

Battery : 12V, 7A
Diode : schottky diode

1) Circuit with one Diode :
Power supply should have 13V, (12+1)
one Volt more than battery voltage,
if no, battery will lose 40mA,

2) Circuit with N-CH mosfet :
works well, cutoff voltage can be adjusted around 11Volt,

3) Circuit with Relay:
works, but not fast as with N-CH mosfet ,
relay drain more power then transistor,

4) Toggle transformer :
very useful circuit , if main transformer voltage drop under 11V (adjustable)
second transformer take its place immediately.

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