Virtaboksi

Virtaboksi

Virtaboksi is a multi-purpose 3-channel common-earth power switch, rating 12–48 VDC, 20 A. It has multiple operating modes:

• Home/away switch supporting three individual groups and is optimized for solar energy off-grid applications.

• Water pump controller with pressure sensor input and control for combined submersible and pressure pump system. Additionally, a throw-over switching capability to drop loads while pumping.

• Generic Modbus RTU server (slave) with 3 solid-state "coils", 3 digital outputs, and 4 digital inputs.

In the picture above the Powerpole connector colors are incorrect. Red is used for inputs and black for outputs. In a real product, the three groups have different colors: red, yellow and blue.

Design principles

• Flexible voltage options; 10–34 V input on first group, 10–60 V on second and third group.
• High current support. With passive cooling, 20 A loads can be controlled. MOSFETs are capable of switching over 100 A continuous current in case where cooling and PCB traces are reinforced.
• Small size: Thanks to transistor control, the size is way smaller than for three contactors of similar rating.
• Low losses: Internal resistance <10mΩ.
• Rugged: All digital I/O ports are short-circuit, reverse voltage and surge protected.
• Power saving: When loads are off, the power consumption is minimal, less than 5mW, allowing it to be left powered on over dark winters.
• Hacker friendly: You can create your own firmware for the STM8 microcontroller, allowing real-time and stand-alone control of your loads and connectivity to other peripherals up to 1 km distance over RS-485.

Operating modes

Home/away mode

Status: 💚 Functional

This unit provides priority output on OUT1 when the switch is in either home or away position. Home controls OUT2 and OUT3 groups and can be used to control two separate voltages as long as they have a common ground.

An example use case is a solar off-grid system with two 12V batteries in series providing 24 volts, plus 12 volts generated from 24V using a step-down DC converter. DC converter is not included in the package.

In that case this switch can be used to turn the loads partially while being away, such as keeping refrigerator running but turning off lights while not present. When using a DC converter, its input is connected OUT1 its output (12V) to IN3.

Maximum voltage in IN1 is 34 VDC. The limitation comes from the internal power supply. In case you want to use higher voltages in IN1, cut the trace F1 on the bottom of this board and power the system directly from a regulated 3.3 VDC supply via the terminals.

IN2 and IN3 are rated for 60 volts maximum, making it possible to control 48V nominal voltage loads. Minimum voltage for all groups is about 10 volts. Under 10 volts, MOSFET control becomes unreliable.

How to connect

In home/away mode, when I1 is shorted to the ground, the oprating mode is away. When I2 is shorted, the mode is home. If both connectors are open, operating mode is off.

Optionally, LED anodes can be connected directly to O1 and O2. They represent home and away operating modes, in that order. There is a current limiter controllable by R1 to limit the maximum current of O1...O3 to about 15 mA by default, so series resistors are not needed.

If your solar controller has a low battery condition relay, it can be connected to I3. When the input is high, the system is forced to off mode, ignoring the state of home/away switch.

I4 is not used in this mode.

Water pump controller mode

Status: 🔬 Hardware OK

Hardware is capable, but no firmware support yet.

Modbus RTU server mode

Status: 🔬 Hardware OK

RS-485 hardware is tested and some firmware tests performed, but no Modbus implementation exists yet.

Building firmware

To build firmware, you need CMake and sdcc. The preparations are very standard CMake stuff. In firmware subdirectory, run:

mkdir build
cd build
cmake ..

And then, make compiles it. Alternatively, make upload to compile and flash.

License

The firmware is free software: you can redistribute it and/or modify it under the terms of the GNU Affero General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

The hardware is provided as source-available: The schematics and PCB layout are provided for reference only. The files can be freely distributed without limitations but no derivative works are allowed without a permission from the copyright holders.