Raspberry Pi jUPS

This is the UPS for the Raspberry Pi.

Used battery type is 12V lead acid, widely available, cheap and not sensitive/dangerous to charge.

Name jUPS because it's just a UPS without 100 complicated features! Simple and functional!

Set boot/shutdown parameters and monitoring battery voltage by serial/USB adapter (this is optional; module is full working without serial adapter).

If you are using Node-RED, set/monitor all by Node-RED dashboard.

Module design is a modular:

• battery charging is performed using the LM2593 CC CV module; charging voltage and current are on the module; attached to the main PCB,
• 5V for Raspberry is realized by the DC/DC step down module; attached to the main PCB,
• contol logic is made by Attiny 1614 microcontroller.

The jUPS microcontroller takes multiple voltage samples over time and calculates the average.

This way the current oscillations on the battery during charge/discharge are eliminated as valid.

Why modular design?

Because all of these modules meets specifications, not expensive and have appropriate dimensions.

Work principles:

*Install python shutdown.py script (see Documentation link).

*If needed, adjust the voltage and current of the LM2596 for your battery!; see the notes at the end of the document.

After full wiring module (DC input, battery and Pi) and turning on the power, the jUPS will start charging the battery and monitoring the battery voltage level.

If the battery voltage is below vH (voltageHIGH), Pi does not start.

After battery reaching vH, Pi is powered up and booting begins.

Full boot provides timeBOOT time, during this uninteruptable time battery level in not monitored.

After that, Pi resumes normal operation.

If the DC(AC) input fails, the Pi runs continuously, powered by a battery. Battery voltage is constantly monitored.

After reaching the value of vL (voltageLOW), GPIO_21 on Pi goes to LOW via a dupont wire between jUPS and Pi.

This causes the shutdown script to execute.

After running the script, timeOFF starts as well.

During the timeOFF time, the battery voltage is not monitored, ensuring that the Pi is turned off properly.

timeOFF is not interrupted.

At the end of Pi shutdown and elapsed timeOFF time, DC/DC goes off (Pi is completely OFF).

Once the DC(AC) input is restored, the battery starts charging and monitoring, wait until it reaches vH, Pi start to boot, .......

All parameters are set via serial/USB adapter (9600,N,1).

*TX and RX are not swapped (connect TX to TX and RX to RX), voltage level is 5V.

Command format is:

<parameter:value>

<> included.

Parameter:

• tB; timemeBOOT; uniteruptable time for properly boot Pi,
• tS; timeSHUTDOWN; uninteruptable time for properly shutdown Pi & shutdown DC/DC,
• vM; voltageMONITOR; enable/disable send battery voltage value via serial/USB adapter in JSON format,
• cA=1; correcting the read value of the battery voltage,
• vH; votageHIGH; battery voltage at which Pi will start to boot,
• vL; voltageLOW; battery voltage at which PI will start to shutdown,
• read; read all settings values
• reset; resetting all parameters to the default values.

Default values:

• tB=45; range is 1-99 seconds
• tS=60; range is 1-99 seconds
• vM=1; voltageMONITOR is ON; for voltageMONITOR OFF, set vM to 0.
• cA=1; reading battery voltage value*1; range is 90-130(0.9-1.3)
• vH=125; 12.5V; range is 90-130 (9-13V)
• vL=110; 11.0V; range is 90-130 (9-13V)

*state of voltageMONITOR is not important for jUPS funcionality!

Some notes: Set LM2596 to meet battery parameters (float voltage and charging current).

See recommended values on the battery/manufacture datasheet.

After find correct value, recommended is to change potenciometers with fixed resistors.

For this, thanks to PCB cut area not need to remove module.

How to set battery charging voltage?

Connect AC/DC to the PCB DC terminals.

Don't connect battery!

Measure voltage on the battery terminals (on the PCB battery terminal!).

Set voltage (with voltage potenciometer) to the recommended value (13.5-13.8V).

How to set battery charging current?

Connect AC/DC to the PCB DC terminals.

Don't connect battery!

Set multimeter to measure current.

Connect probes to the battery terminals (on the PCB battery terminal!)..

Set current (with current potenciometer) to the recommended value (0.1C; e.g for 1.2Ah se to 0.12A(120mA)).

The module is delivered set at about 13.65 V and 150mA.

cA is also set to the nearest value.

It is recommended to use fuses like in block diagram!

*Usually on AC/DC power supply, fuse is already integrated.

*For battery fuse, easyest way is to use in-line fuse holder between battery terminal and PCB battery + terminal.

jUPS module PCB is inside green area!

Everything outside this area is not included!

If you use Node-RED it is possible to make shutdown via exec node instead via GPIO_21.

For this, vM must be set to 1;. See example flow (Documentation link).

Also for Node-RED users, in documentation is flow for set all parameters via dashboard.

AC/DC rectifier:

-DC output voltage must be 1.5 V above the battery float voltage.

DC/DC step down specification:

• input voltage range: 9-35V DC

• output voltage: 5V; usually 5.05-5.15V

• max output current:5A; tested at 3A for a long time, stable voltage and very very low heat.