Hello, on an active building site i have a few stands with some monitoring sensors, rpis, cameras etc used to monitor the build process, prevent theft etc. There are occasions, when the mains electricity has to be turned off for safety.
In there have a small switching module (https://www.aliexpress.com/item/4000038641968.html), that switches between power in case of mains failure. Primarily it is using 12VDC power coming from power adapter powered by mains 230VAC, in case there is an electricity outage it switches to backup power from 12V traction lead acid battery. Lead acid battery is charged by simple "refresher" lead acid battery charger (one of the stands have also 18V 100W solar panel with charger controller for lead acid batteries). Its what i had home, so i used those.
This refresher chargers are not powerful enough to provide current to handle the load, and after some time throw out a fault and stop charging completely. So i cannot use it in a way where i power all directly off the battery.
The problem with the switching modules is, that they do not switch the power without interruption. There is a short, maybe 0.5 seconds delay, which causes all the electronics to reset.
--------- question starts here ------------
So the voltage is 12VDC. As a test i have added 25V 10000uf capacitor and 45V 20A schottky diode (its what i had home) "between" the module and the load. This is enough to keep the electronic to survive the short interruption. However to have this circuit to be somewhat complete, i would like to add a capacitor discharge resistor and probably a NTC thermistor to limit the inrush current when first charging the capacitor.
I do have a 5W 2000Ohm cement resistors at home, so i think those should be ok as discharge resistors. If not , what discharge Resistor should i use ?
Question is, what NTC thermistor (value, type, etc) should i use to limit the inrush current. A direct link to ali is ok, but i can find it myself.
Very simple picture of the circuit in attachement.
I dont want to spend too much additional money to buy a different chargers, modules, etc.
I do not want to directly connect the 12V power adapters to the battery.
Any other tips, connection shemes etc are welcome.
Thanks.
In there have a small switching module (https://www.aliexpress.com/item/4000038641968.html), that switches between power in case of mains failure. Primarily it is using 12VDC power coming from power adapter powered by mains 230VAC, in case there is an electricity outage it switches to backup power from 12V traction lead acid battery. Lead acid battery is charged by simple "refresher" lead acid battery charger (one of the stands have also 18V 100W solar panel with charger controller for lead acid batteries). Its what i had home, so i used those.
This refresher chargers are not powerful enough to provide current to handle the load, and after some time throw out a fault and stop charging completely. So i cannot use it in a way where i power all directly off the battery.
The problem with the switching modules is, that they do not switch the power without interruption. There is a short, maybe 0.5 seconds delay, which causes all the electronics to reset.
--------- question starts here ------------
So the voltage is 12VDC. As a test i have added 25V 10000uf capacitor and 45V 20A schottky diode (its what i had home) "between" the module and the load. This is enough to keep the electronic to survive the short interruption. However to have this circuit to be somewhat complete, i would like to add a capacitor discharge resistor and probably a NTC thermistor to limit the inrush current when first charging the capacitor.
I do have a 5W 2000Ohm cement resistors at home, so i think those should be ok as discharge resistors. If not , what discharge Resistor should i use ?
Question is, what NTC thermistor (value, type, etc) should i use to limit the inrush current. A direct link to ali is ok, but i can find it myself.
Very simple picture of the circuit in attachement.
I dont want to spend too much additional money to buy a different chargers, modules, etc.
I do not want to directly connect the 12V power adapters to the battery.
Any other tips, connection shemes etc are welcome.
Thanks.
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