Hello and thanks for your time reading my post.

I've my router connected with its adapter and a battery for backup. Details: The adapter output 15V and 0.4A The battery output 12V and 12A The router needs: 9V and 0.6A (I've a regulater to minimize 12V to 9V to fit router needs).

Now, if I connect the router's adapter with battery then to the router, the router will take power from where? The adapter or the battery?


  • \$\begingroup\$ If you the circuit inside the router that connects the two power sources to the other circuits, then we can answer this question --- please provide a schematic. \$\endgroup\$ – The Photon May 11 '15 at 2:15
  • \$\begingroup\$ @ThePhoton Thank you for your time, I'm not Electrical Engineer so I can't do or provide shema for that. But bigjosh has answered my question :) \$\endgroup\$ – Mohammad AlBanna May 11 '15 at 14:41

The adapter will power the router, but also try to charge the battery since it's voltage is lower. This could be bad depending on what kind of battery this is.

You can use diodes to prevent the power from one power source from going to another power source. In this case, the router will get power from which ever source is supplying a higher voltage.


simulate this circuit – Schematic created using CircuitLab

In this configuration, the adapter will power the router for as long as it is plugged in, if the adapter looses power then the battery will take over and the router will keep running (at least until the battery goes dead).

You can use pretty much any diode that can handle current needed - which is the current needed by the router plus the current wasted by the regulator.

  • \$\begingroup\$ Thank you very much for your answer, I can do that as I'm not Electrical Engineer but I could understand your answer. I think one diode will be enough from the battery to adapter, I don't mind if the adapter could charge "at least" the battery even if it was a little. \$\endgroup\$ – Mohammad AlBanna May 11 '15 at 14:43

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