I have a 12v router feeding from a 12v power adapter. I installed a 12v relay to switch over to a 12v deepcycle lead acid battery when the power goes of. When the power goes off, the router turns off and I must turn it on manually. I have measured the voltage over the relay switch and it drops to between 5 and 9 Volts when switching. When the power comes on again, the router stays on. How can I prevent this drop in voltage when switching to the battery (battery voltage is about 13.8v).

 

Sounds like the battery does not have the capacity to run the router.

What is the current requirement of the router and the capacity of the battery?

 

I have a 12v router feeding from a 12v power adapter. I installed a 12v relay to switch over to a 12v deepcycle lead acid battery when the power goes of. When the power goes off, the router turns off and I must turn it on manually. I have measured the voltage over the relay switch and it drops to between 5 and 9 Volts when switching. When the power comes on again, the router stays on. How can I prevent this drop in voltage when switching to the battery (battery voltage is about 13.8v).

Do you mean that it drops during the changeover Then immediately returns to the correct value?
Why don’t you keep the battery float charge and run permanently off the battery?

 

I have measured the voltage over the relay switch and it drops to between 5 and 9 Volts when switching.

What do you mean "over"?
Exactly how did you measure that voltage?

 

Sounds like the battery does not have the capacity to run the router.

What is the current requirement of the router and the capacity of the battery?

Router current is 1 amp and the battery is brand new and full time on trickle charge - capacity is 110ah.

 

What do you mean "over"?
Exactly how did you measure that voltage?

The relay is connected with the NC connected to the power adapter (12v). Power input from 12v adapter connected to NC terminal of switch and output through the Common terminal to the router. Power input from the 12v battery connected to NO terminal of switch and output the Common terminal to the router. I tested with an AVO between the NC and Common and between the NO and comment respectively when the relay is turned on and of. Hope this help. Thanx for helping a pensioner.

 

What I see, based on that description of the connections, is that there is a time with no power applied during the transition.
I suggest an alternate scheme in which the power is not switched, but is supplied thru diodes of adequate current rating. I suggest a 5 amp rating to be conservative. Possibly a schottky diode from the power adapter to provide a lower voltage drop.

It is also entirely possible that there is an inadequate wire size in one of the wires.

The second advantage of the diode change-over scheme is that it does not consume any power in the standby mode.

 

What I see, based on that description of the connections, is that there is a time with no power applied during the transition.
I suggest an alternate scheme in which the power is not switched, but is supplied thru diodes of adequate current rating. I suggest a 5 amp rating to be conservative. Possibly a schottky diode from the power adapter to provide a lower voltage drop.

It is also entirely possible that there is an inadequate wire size in one of the wires.

The second advantage of the diode change-over scheme is that it does not consume any power in the standby mode.

Thanx so much. I will try that.
Kind regards.

 

What I see, based on that description of the connections, is that there is a time with no power applied during the transition.
I suggest an alternate scheme in which the power is not switched, but is supplied thru diodes of adequate current rating. I suggest a 5 amp rating to be conservative. Possibly a schottky diode from the power adapter to provide a lower voltage drop.

It is also entirely possible that there is an inadequate wire size in one of the wires.

The second advantage of the diode change-over scheme is that it does not consume any power in the standby mode.

Change it to a 15V adaptor, if it will run off that much voltage, and you have a working idea. With a 12V adaptor and a 13.8V battery is going to be permanently powered from the battery (until the battery goes flat)

 

Change it to a 15V adaptor, if it will run off that much voltage, and you have a working idea. With a 12V adaptor and a 13.8V battery is going to be permanently powered from the battery (until the battery goes flat)

Thanx for the reply. I will try that. Kind regards.

 

Thanx for the reply. I will try that. Kind regards.

The older, non-switch mode, wall warts only dropped to the marked voltage when the specified current was drawn. so no telling. BUT that is a good suggestion.

 

The older, non-switch mode, wall warts only dropped to the marked voltage when the specified current was drawn. so no telling. BUT that is a good suggestion.

Off load, you could easily get 17V from a 12V supply. In fact the output impedance was so high they could be used as a constant-current battery charger.