Heatweb BEMS Hat

Feature	Specifcations
Controller compatibility:	Raspberry Pi, all models Beaglebone Black ESP32 None (stand alone Modbus Slave Mode)
Controller interface:	Raspberry Pi header I2C communications to controller 3x UARTs 5V power to controller External watchdog to controller
8 x thermistor inputs	10k resistance temperature devices
4 x universal inputs	DIP selected mode 100Hz pulse signals (count and frequency) volt-free contacts 0-10V signals 1k or 10k thermistors
4 x volt-free / pulse inputs	100Hz pulse signals volt-free contacts State, counter and frequency readings
4 x PWM inputs	DIP selected pull-up resistors (5V) Voltage comparator Low state: < 3V High state: 3V to 24V
4 x Digital PWM outputs	Pull-down operation DIP selected pull-up resistors (5V/24V) Diode protection for connection to relays
4 x 0-10v outputs	10mA peak current
2 x change-over relays	10A @ 36V
2 x RS485	Independent lines for Modbus or bespoke protocols DIP switch selectable terminating resistors One line DIP switchable for Modbus Slave Mode
1 x M-Bus	For meter communications On-board supply: 36V @ 30mA Short-circuit protection Device limit: 10
Power Supply	Nominal voltage: 12VDC Current requirement: 3A Minimum supply voltage: 11.8V Peak supply voltage: 16V
Battery support	On-board rechargeable battery socket Maintains power to all systems (5V, 24V & 36V) during loss of supply Voltage monitoring with safe shutdown Duration: > 1 hour (can be extended with use of sleep mode) Battery: 18650 Lithium-ion Rechargeable Cell - 2500mAh 3.7V 20A
Real time clock	Battery:CR2450 Coin Cell
General purpose input button
3 x user definable LEDs
Fan control and connector
Dimensions	Length: Width: Height:

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  Raspberry Pi Compute CM4 Base Board

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About

The Heatweb BEMS Hat runs from a 12v dc supply, generating 5v for the board, 24v for valves, and 36v for M-Bus, using on-board dc-dc converters backed up by a rechargeable battery.  A coin cell is used to power a real-time clock.

WiFi, Ethernet and Bluetooth are provided by the parent controller board.

A number of the inputs are universal, and can be switched between NTC, 0-10v, or volt-free / pulse inputs (jumper selected).  This ability to alter the hardware setup increases versatility significantly.

The addition of M-Bus allows us to connect to heat meters as standard, making the board a stand alone solution to open-sourcing meter data, and to use meter data within control logic.  

The battery backup allows us to safely shut-down all valves and the controls when power is removed.  This overcomes a common problem with HVAC systems, where valves typically remain open, destroying network performance.

Schematic

Resources

• https://github.com/heatweb/plumbing-controller
• https://github.com/SequentMicrosystems/ti-rpi/
• Modbus Registers
• Waveshare CM4-IO-BASE-A
• Waveshare CM4-IO-BASE-A Wiki
• Wiring Diagrams
• Wiring Editor