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Power and the grid

The power to the house is from the National Grid and our solar panels.

240V AC mains power

In the UK mains power is supplied from the National Grid. Alternating Current (AC) as voltage and current input is supplied as a nominal sinusoidal voltage of 240v RMS at 50 Hz with a peak to peak of about 338v. In reality this varies between 216 and 253 RMS. The voltage from the Grid goes from 0 volts to +338 volts down to -338 volts in 20 milliseconds. It repeats this 50 times a second (1000ms).

Resistive load

On the very simplest level a house is a resistive load. The voltage inside your house will follow a similar sinewave voltage at a slightly lower voltage because of the resistance in the wires of the Grid and inside your house.

Mains 240V AC ->
--> House Load AC

The voltage at the substation (on the Grid) will be more than that at the resistive load of the house and therefore the current will flow into the house from the Grid, through the electricity meter.

Grid tie inverter

Solar panels on the house generate electricity as Direct Current (DC). DC is fed in to a Grid tie inverter. The inverter inspects the sine wave voltage that is generated by the Grid as seen at the resistive load of the house and creates a matching sine wave voltage  slightly above that of the house. This will cause current to flow from the Grid tie inverter through to the house and if there is enough power from the solar panels, out onto the Grid.

Grid <--
<-- Grid tie inverter

So the power consumption of the house will approximate to 240Volts RMS multiplied by the current into the house from the Grid plus that  from the Grid tie inverter from the solar panels. Because the loads used in the house are not purely resistive this is not the whole store but it is a fairly good approximation.

Power management and current flow

To truly calculate the power usage, we would need to measure the voltage and the current profile throughout each cycle. In power management our aim is to manage the current supplied to the house so that we may use locally generated current rather than draw from the Grid. Power management rather than accurate power monitoring. Knowing the current flow is sufficient to achieve this if we also know the direction of flow. Both the Grid tie inverter and the National Grid will determine the voltage dynamically but use of the 240V RMS value will suffice to estimate power usage for our power management needs. Some electricity meters offer an LED that becomes solid lit when current is flowing out of the house and pulses when current is consumed by the house.

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CU monitor redesign ?

The latest PCBs for the CU monitor arrived this week. They were supposed to be the test batch to prove the release of the CU Monitors to the website. There followed a frustrating two days of soldering up and testing. Essentially I had the surface mount ADS1115 that needed to be soldered onto the board. These are tiny chips that can be tricky to solder. After soldering 3 boards I had one that worked intermittently and two that just plain failed to work. So I looked at the working one on the bus analyser and the timing of the I2C bus seemed to be causing a lot of NAKs. After tweaking the software driver, this became a lot more reliable, which suggested the bus layout on the PCB was bad! making the communication timing marginal.

This means this will not be the last board! This got me thinking. The ADS1115 is a fairly low cost  16 bit A to D converter, initially I chose this chip because it was a module that lends itself to rapid prototyping but it has 4 channels and is accessed across an I2C bus. This chip  has caused me to redesign the CU Monitor PCB in the past because we are reading more than one channel rapidly it can cause significant slow down in the sample rate. Currently the CU monitor only uses one of the channels to boost the read speed. This makes this chip way over specified for our purpose.

So I intend to reassess the use of this chip and I will create a sequence of design/posts and explain my design decisions to document this procedure and help me get it straight in my mind

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Web RD

Web RD a simple development project aims to connect a display as cheaply as possible to the internet. This development is intended for anyone wishing to display information available online without actually requiring a separate device. The Web RD PCB is available in our store. This will allow you to build your own project without recourse to hardware design. The Web Rd development consists of :

  • CP2102 USB to TTL Serial Converter
  • WebRD PCB or Assembled WebRD Module
  • MAX7219 Dot matrix LED Display
  • USB Male to Female Extension lead
  • ESP8266 ESP01S

The CP2102 is a low cost stable and reliable way to connect a project to the power providing both 5V and 3.3v outputs. I’ve run them for thousands of hours with no problem. Powering a Project can can be an issue. This piece of test gear does the trick nicely.

The MAX7219 Dot matrix LED display is the low cost way to display large text.

The ESP8266 ESP01S is a very capable processor that provides plenty of processing power and a very cost-effective way of connecting to the internet.

We have available in our store 3d printed enclosures that provide housing for the display available in a mixture of colours

There are many use cases that make use of the Web Rd

  • Web Clock
  • Network connectivity display
  • Twitch Account display
  • UTube account display
  • Stock price ticker

For more information see

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CU monitor

The CU monitor is a development designed to calculate the current flowing to the consumer unit  from the grid and solar panels, broadcast is within the LAN and record the data to a website. I have taken a minimalist approach to keep the costs down. It uses two current clamps to measure the current

 

Current clamp sensor

One is clipped around one of the single core cables to the consumer unit into the house from the grid and the other other is clipped around the one of the single core cables that come from the solar panels inverter.

These connections provide the minimum number of connections. We have an algorithm that predicts whether the grid connection is importing or exporting to the grid from the profiles of the currents observed on these clamps.

The CU monitor also provides an optional photo resistor input that can be blue tacked to the front of your electricity meter as some electricity meters have an LED that becomes illuminated when power is being exported to the Grid. This can offer a confirmation that our algorithm is correct.

CU monitor Hardware

The CU monitor kit comprises our own PCB which hosts a processor that is used to calculate the AC current flow and records it to our display website. The PCB may be powered either by a USB lead or via a 240V mains power plug. The electronics are housed in an IP55 mini Junction box.

USB connection kit (no soldering required)

  • CP2102 USB to TTL Serial Converter
  • 2 or 4 Female to Female Jumper wire
  • USB extension cable
  • USB Cable
  • USB power brick or available USB socket

Mains powered kit (minimal soldering):

  • Hi Link 3.3V  3W P/N HLK-PM03
  • Varistor
  • Power Block

Either power system will suffice. The USB connection requires no actual soldering and  does not require the user to handle mains AC power. If you are comfortable  wiring into the mains power then the other kit is available.

disclaimer: handling mains voltage can be very dangerous. Do not do so unless you are qualified and comfortable with the wiring and connecting of mains power.

 

 
IP55 mini Junction box
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Solar panels

Many years ago I joined the Government’s FIT scheme and had solar panels installed. They have worked well so far but we only had a vague idea of how the energy they produced was being used. So I decided to develop a device to quantify and record the power usage. I wanted to make this device available to other owners of solar panels who may wish to find out more about quantity of power they produce from their solar panels to know how to predict their future usage.

The CU monitor is my attempt to make the energy usage profiles that our solar panels produce easily accessible. This will allow me to make informed choices on electrical power questions.

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Energy management

Whatever the outcome of the EPC and the RHI review I would like my house to be more effective at energy management. The Legacy Solar system cannot be touched without jeopardising the FIT payments for the power we generate. My solution is to create a development that will broad cast the energy usage as seen at the consumer unit and indicate whether the we are exporting to the Grid or consuming. The RHI review will probably require an electric power consuming solution and being able to effectively control this would make a big difference.

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Goals aims and reasons

I am an Engineer educated in Chemical Engineering, Electronic Engineering and Software Engineering. I can see solutions to problems that no one  is solving. This website  it my attempt to take my solutions an share them with the world perhaps this is pretentious and no one will want my solutions and I’m OK with people who think that. Perhaps my solutions will genuinely help people (which is my hope) and if I can make a little money from the venture that works for me.

Solutions and their  focus:

  • Renewable energy : I think everyone needs to make this a priority and I have electronic solutions for people with legacy solar systems to try to optimise energy generation and usage.
  • Electronic and or software projects: These are solutions I am developing to problems I see. Mainly IOT and Domestic LAN in scope.
  • Gaming: There are solutions to Fantasy Role Playing games like D&D or Online Gaming that I have solutions to.

I will document the problems and my solutions to them is this Blog.