Raspberry Pi and Power Monitoring with RS485 Interfaces

Posted by Vytas Sinkevicius on

Power Monitoring in commercial applications such as data centers, utility rooms for buildings, lighting controls, etc. use multi-branch current monitoring circuits and voltage meters. Here is project that I am starting using the Raspberry Pi as the main controller in a Branch Current Monitor system.

The main items from left to right are:

  • Raspberry Pi 3
  • Pi-SPi-RS485 Interface
  • VP-EC-BCM Interface
  • 18 Channel Current Sense Transformer Breakout PCB
  • Current Sense Transformer

The heart of the project is the RPi3. The software will be written in "C" using the "Geany" compiler.

 

The Pi-SPi-RS485 Interface is used to communicate and provide power to the VP-EC-BCM Interface. By using the RS485 and Modbus RTU protocols, the RPi and Pi-SPi-RS485 combo can be located up to 4000 feet away from the location where the monitoring is to take place.

The heart of the current monitor is the VP-EC-BCM Interface from VP Process Inc. This is a 36 channel current sense transformer converter with 3000 VAC Isolation between the primary circuits and the RS485/Power Interface.

Here is the PCB:

Here is the pcb in it's DIN rail enclosure:

 

Here is a closeup of the 18 channel current sense transformer breakout pcb:

I covered the details of this interface in a previous blog post found here.

Finally, here is a close up of the current sense transformer that is going to be used:

This is a Split Core Current Transformer Model: CR3110-3000 manufactured by CR Magnetics.

There are two types of current sense transformers: solid core and split core. The solid core types require the wire carrying the current to be passed thru the "donut" of the transformer and is ideally suited for new builds and conditions where the main power can be turned off, the breaker wire removed and re-connected with the current transformer attached.

The split core transformer is ideal for applications that are currently in use and where the power wiring to the breakers cannot be removed. As shown in the picture above, the top half of the transformer un-clips, the transformer is placed around the breaker wire to be measured and the top half of the transformer is clipped back into place.

Details for the CR3110-3000 can be downloaded in PDF format here.

This project scope is to measure, monitor and datalog the following AC currents in a residential application:

  1. Electric Hot Water Tank (220 VAC) Phase A
  2. Electric Hot Water Tank (220 VAC) Phase B
  3. Heat Pump (220 VAC) Phase A
  4. Heat Pump (220 VAC) Phase B
  5. Kitchen Range (220 VAC) Phase A
  6. Kitchen Range (220 VAC) Phase B
  7. Kitchen Refrigerator (117 VAC)
  8. Freezer (117 VAC)
  9. Hot Tub (117 VAC)

Further posts will follow this project - installation, application code, data logging and tracking.


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  • I’ve been playing with mbusd from sourceforge, nodered with Modbus library and linking it to Domoticz for my home automation. I have some Modbus PLCs which i am trying to do something interesting with.

    Bob H on

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