Electronic development

12V Uninterruptible Power Supply (UPS)

12V battery CCTV Electronics

3 Apr, 2021

Description

Electronic device that provides battery back-up, when the electrical power fails, to a wifi modem and CCTV system. The uninterrupted power supply (UPS) system provides enough power for several hours (depending of battery capacity) with a stable voltage of 12V.

The UPS implements a 12V rechargeable sealed battery and a set of electronic circuits responsible for maintaining a stable output voltage, charging the battery and protecting it against over-discharge or over-current.


Features

  • Battery protection: over-discharge and over-current protection to avoid draining the battery below the recommended voltage and prolonging its life cycle.

  • Voltage regulator: equipped with automatic 12V voltage regulator to stabilize output voltage under electrical power or battery fluctuations.

  • Battery charger: built-in constant current and constant voltage (CC/CV) battery charger

  • Automatic operation: the system automatically switches to battery when it detects that there is no electrical power and auto restart while AC recovery.


Basic indication table

Status Blue
LED		 Red
LED		 Green
LED
Back-up mode
Normal mode
Regulator error
Battery recovery
Battery protection error

LED ON       LED OFF



Block diagram and operation

The operation of the system is divided into two segments according to electric power.

  1. Normal electric power: in this stage the operation is as shown in Figure A. The UPS will charge the battery automatically; the power supply is connected to the city power and its output goes to the commutator. Because there's electrical energy, the commutator contacts are connected to the power supply, then its ouput goes to a 12V regulator and finally give power to the ouput devices.

  2. Back-up mode: in this stage the operation is as shown in Figure B. Because there's not electrical energy, the power supply and battery charger doesn't work; the commutator contacts are connected to the battery protection circuit and then its ouput goes to the 12V regulator wich supplies the ouput devices.

Measurements

The characterization of the UPS system and its behavior over time are presented below, through a monitoring circuit. The circuit carried out the respective measurements, saved the information in a microSD memory in a stipulated time interval and then it was processed with a python and Excel script (see more information in the following repository). For the following battery charge and discharge curves, place the cursor on the graph to interact with it.



3hrs 42min

Battery duration


1hr 14min

Battery recovery


30s

Sampling period


1.25A

Consumption current


33.35°C

Temperature


16hrs 25min

Recharge time

Data description

  • Battery duration: total time that the UPS system can keep the devices energized, when the electric power fails, with the battery fully charged.

  • Battery recovery: time the battery is available (when charging) for use again after being fully discharged.

  • Recharge time: time the battery is fully charged after being fully discharged.

  • Consumption current: average current to which the battery discharge curve was subjected.

  • Temperature: average ambient temperature at which the monitoring of the charging and discharging battery curves were carried out.

  • Sampling period: time interval between two successive samples.