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how to create autoswitching circuit for 12v ups for router

Usamaj

Jul 14, 2022
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hello friends i am new here i want to create a circuit that do auto switching in nanosecond i want to mosphet not relay is it possible if yes what should i do .. the main use of it to automatically switch to battery when there is no electricity (adaptor off ) when the adopter is on so the load transfer to the adopter and charge the battery this project for 12v router i need help :)


""Hello how are you i am working on a project making ups for the router so i am stuck at auto switching how can i create it without relay (because its delay time restart the router) so which things i need to create the circuit .... there is 2 power source 12v adopter and 12v battery pack so i want to use 12v adopter as a primary power source and when the electricity cut the modem switched to battery without to much delays that restarts it .. please i need help""



[ Mod Note combined 2 intro posts from 2 threads on same subject]
 
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Harald Kapp

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Simply use 2 diodes:
upload_2022-7-14_13-12-22.png
Make sure the voltage from the power supply is a bit higher than the voltage from the battery.
 

kellys_eye

Jun 25, 2010
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Simple blocking diode if the difference between the battery and adapter voltage is 0.7V or so.....
 

crutschow

May 7, 2021
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If the 12V adapter voltage is slightly higher than the battery voltage, you could use a Schottky diode at each output to isolate the load.

If the adapter can tolerate the battery voltage on its output when it is unpowered, than you only need one diode.

If adapter voltage is not larger than the battery voltage, then you could use a P-MOSFET controlled by the adapter voltage to connect the battery, with a diode to isolate the adapter.
 

AnalogKid

Jun 10, 2015
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A relay will work if you add a large capacitor. Measure the current drawn by the router when it is operating normally. This will be less than the input current rating on its label, and determines the size of the capacitor.

ak
 

Usamaj

Jul 14, 2022
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okey thanks, but i have how it works. what happens when power and battery both providing current how it auto switch
 

Usamaj

Jul 14, 2022
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If the 12V adapter voltage is slightly higher than the battery voltage, you could use a Schottky diode at each output to isolate the load.

If the adapter can tolerate the battery voltage on its output when it is unpowered, than you only need one diode.

If adapter voltage is not larger than the battery voltage, then you could use a P-MOSFET controlled by the adapter voltage to connect the battery, with a diode to isolate the adapter.

I really Thanks Full for your response i am new in this could you please draw a rough circuit.
 

Usamaj

Jul 14, 2022
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A relay will work if you add a large capacitor. Measure the current drawn by the router when it is operating normally. This will be less than the input current rating on its label, and determines the size of the capacitor.

ak
Yes relay will work but it took to long to switich almost 1 to 2 second and in this time router will restart so i dont want that
 

Usamaj

Jul 14, 2022
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Simple blocking diode if the difference between the battery and adapter voltage is 0.7V or so.....
i am following this video, but i want to transistor

 
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Harald Kapp

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The power source with the higher voltage will provide power through the associated diode. The output voltage then will be high enough to block current though the diode to the source with the lower voltage. That is why the power supply's voltage has to be a bit higher (e.g. by 0.5 V or so) than the battery's voltage.
You may read up more here, although I'm afraid that's a bit too detailed :(.
 

crutschow

May 7, 2021
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i am new in this could you please draw a rough circuit.
As I said, it depends upon the relative voltage between the power supply and the battery.
Which voltage is larger and by how much?
 
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