12V Uninterruptible Power Supply

This 12V uninterruptible power supply initially designs to drive my fiber optic modem/router. The key reason to build this power supply is to get continuous internet and phone connection during power failures. Core components of this power supply are a constant voltage charger, 12V DC power supply, AC line monitoring unit, and 12V high capacity sealed lead-acid battery. The entire system designs using locally available components.

Prototype version of 12V UPS system

The charging circuit of this system builds around using the popular LM350 voltage regulator. This regulator calibrates to provide both 14.4V fast charging and 13.6V trickle charging. Based on the condition of the battery, the MCU will determine the appropriate charging mode.

At the online state, the LM2576-12 switching regulator provides 12V output to the driving system. (in my arrangement, a fiber optic router).

Block diagram of the 12V UPS system

The PIC16F688 MCU monitors the AC line and battery to controls the output voltage of the LM350 regulator and the output relay. The firmware of this MCU written using the Microchip XC8 compiler, and all the source code and configuration files are available to download at the project repository at GitHub.

The sealed 12V lead-acid battery is the most crucial component of this unit. 12V, 9Ah battery is the most recommended for this system. At the time of this writing, this battery cost around Rs. 3500 (US$ 17.60), and I bought it from a local online store.

In online mode, this system provides 12V output. In offline mode, if it has a fully charged battery, it delivers an output of 12.5V.

This uninterruptible power supply is suitable for appliances that need 12V - 13V input with a maximum of 2A current. With the configuration described above, this system continued to power my Huawei HG8245H5 fiber optic router for more than 7 hours.

This power supply unit is an open hardware project. All the schematic, PCB design files, firmware source codes, and compiled binaries are available to download at the project repository at GitHub.

Assembling the circuit

In the provided design, all the parts used in the PCB are through-hole-type components. For this design, we used low-cost and commonly available electronic components.

The recommended transformer for this system is the 230V to 15V×2 (5A) and 12V×2 (500mA) step-down transformer.

Install adequate heatsinks for LM350, LM2576, and 7805 regulators. To minimize the space, we recommend using a single heatsink for LM350 and LM2576 regulators. If using a single heatsink, always be sure to install ceramic and mica insulators to the LM2576 regulator to eliminate short circuits.

The PCB provided with this project is design to be constructed using a single-sided copper board. The dimensions of the PCB are 131.7mm × 100mm.

Use 1% ¼W metal film resistors for R3, R7, and R8 to get accurate results. For R2 and R4, use 3W or higher rated ceramic cement resistors.

Calibration and testing

Before connecting the load and battery to the system, it is necessary to follow the below steps to calibrate the system.

Remove PIC16F688 MCU from the U2 socket.
Short circuit pin 1 and 7 of the U2 socket.
Connect digital multimeter to the cathode of the D3 diode.
Set RV2 until the multimeter indicates 13.6V.
Connect pin 7 and 14 of the U2 socket.
Now adjust RV3 until the multimeter indicates 14.4V.
Connect PIC16F688 MCU to the U2 socket.

After finishing the above steps, connect the 5V UART-to-USB adapter to the J6 debug terminal and initiate the serial terminal with a baud rate of 1200 with an 8N1 configuration.

Test setup of the 12V UPS system

Connect the digital multimeter to battery terminals and adjust RV1 until the serial terminal shows the ten times voltage reading of the digital multimeter. (Example: 12.6V is displaying on the serial terminal as 126)

After the above calibration, the system is now ready to use. Initially connect the battery to the system, and leave it until it got fully charged.

This PCB directly connected to the AC mains, and always be sure to use the necessary precautions when reading voltages and at the calibration.

CD2003 - yet another simple FM radio receiver

In the last few days, we are looking for some simple FM radio receiver to integrate into one of our ongoing projects. For that, we try several FM radio receiver ICs including TDA7000, CD2003/TA2003/TA8164, CXA1019, and KA22429. Out of all those chips we select CD2003 (or TA2003/TA8164) based receiver for our project because of its simplicity and outstanding performance. Except to CD2003, Sony CXA1019 also perform well but we drop it because of its higher component count. We design our receiver based on Toshiba TA2003 datasheet and later we try TA8164 and CD2003 with the same circuit. Either CD2003 or TA8164 can directly replace TA2003 IC, and as per our observations, TA8164 gives excellent results out of those 3 chips. A prototype version of CD2003 FM radio receiver The PCB design and schematic which we used in our prototype project are available to download at google drive (including pin-outs of crystal filters and inductors ). Except for CD2003 IC, this receiver consist...

Arduino superheterodyne receiver

In this project, we extend the shortwave superheterodyne receiver we developed a few years ago . Like the previous design, this receiver operates on the traditional superheterodyne principle. In this upgrade, we enhanced the local oscillator with Si5351 clock generator module and Arduino control circuit. Compared to the old design, this new receiver uses an improved version of an intermediate frequency amplifier with 3 I.F transformers. In this new design, we divide this receiver into several blocks, which include, mixer with a detector, a local oscillator, and an I.F amplifier. The I.F amplifier builds into one PCB. The filter stage, mixer, and detector stages place in another PCB. Prototype version of 455kHz I.F amplifier. In this prototype build, the Si5351 clock generator drives using an Arduino Uno board. With the given sketch, the user can tune and switch the shortwave meter bands using a rotary encoder. The supplied sketch support clock generation from 5205kHz (tuner f...

Experimental narrowband FM receiver for 2-meter band

This project is about MC3362 and ADF4351 based modularized, 2-meter narrow band FM receiver. In this design, the receiver splits into three modules as RF preamplifier, MC3362 tuner, and ADF4351 oscillator. The RF preamplifier builts around BF900 dual-gate MOSFET. The tuner stage builts using the popular MC3362 , low power narrowband FM receiver IC. For the oscillator, we use the ADF4351 DDS RF signal generator module. The core component of this receiver is MC3362 IC. This IC was designed by Motorola and is no longer in production, but this IC is still available to purchase in many online stores . The chip we used in this receiver was purchased from a local electronic component store for LKR 75 (USD 0.2). The RF preamplifier used in this receiver extracts from the N.Ganesan's (VU3GEK) LRR200, 2-meter band FM receiver project . Prototype version of the RF preamplifier. In this prototype, the above preamplifier was built as a module using a Manhattan construction technique. Th...

Dilshan R Jayakody’s Web Log

Search This Blog