Category Archives: Projects

Solar Charge Controller – Monitoring

In an effort to help move the Solar Charge Controller project forward, I’m setting up a mini Solar System in the workshop. The purpose of the system is to charge two 12v 7AH lead acid batteries, that will power a 12v circuit in the workshop. Some basic monitoring devices, battery chargers and LED lights will be operating on this 12v circuit.

Using the Solar Charge Controller that was purchased a few weeks ago, it will charge two 12v 7AH lead acid batteries. These batteries will be connected in parallel to get maximum current.

Initially the Solar Charge Controller will be connected to a single 5W Solar panel, but will be replaced with 2 x 10Watt panels in the future. So why two panels? Well because the roof of the workshop is pitched, the plan is to have a panel on both sides, wired in parallel. Yes, I know that connecting them in parallel will reduce the overall voltage but it will maximise the current used to change the batteries.

5 Watt Solar Panel Change Calculations

Assuming that where only one 12v 7AH battery is connected with the 5 Watt panel, the best current that it can deliver is 0,3A, . Thus it will take 7Ah/0.3A = 23.3 hours to charge. This is the best case situation. When we have two batteries connected, it will take twice as long to change (almost two days). So in this configuration, we won’t be able to draw much from our battery pack. This 5W panel will be used for a later project, but at the moment it will be fine to get this little project up and running.

10 Watt Solar Panel Change Calculations

Assuming that we have only one 12v 7AH battery connected with the 10 Watt panel, the best current that it can deliver is 0,6A. Thus it will take 7Ah/0.6A = 11.6 hours to charge. This is the best case situation (with two 1- Watt panels this is now down to 5.8 hours). In reality this would never happen, as there wouldn’t ever be a situation where both panels had equal current flowing to deliver the necessary 1.2A. I’m hoping that when installed, there will be enough power delivered to keep the battery pack charged and able to run the monitoring system and a couple of 12V LED lights.

With the batteries connected in parallel and the solar panel also connected in parallel, I want to record the actual current flow into the batteries during the day, as well as recording the current flow out of them at night. Before I get the Retro Computer built, I’m thinking of using an Arduino to monitor the system.

Environmental Factors

I also want to record the temperature of the solar panel, as the efficiency of the panels is determined by temperature. As wind has a correlation to the temperature of the panel, it may be necessary to record wind speed as well. Although there may be sunlight, if the panels gets too hot, they are less efficient and having a cool wind blowing will help keep the panel temperature down. This brings me to the last item I want to measure, which is solar radiation (how much sunlight there is).

This simple setup should help provide the necessary information helping me to design my own Multi Purpose Charge Controller (I would like to take power from wind in the future, for days where there is little sun).

Hopefully getting this type of information will prove useful when deciding whether or not to move onto something larger. I’m hoping it will help me to choose which type of solar panels will work best for the workshop.

Input Signals

To begin with, I normally make a list of the input signals that I want to monitor. Then I make a list of the various outputs needed, as this may add more inputs signals that I need.

Current Sense Inputs
  • Current from Solar Panels to Charge Controller (Analogue).
  • Current from Charge Controller to Battery Pack (Analogue).
  • Current to the Load (Analogue).

For these current sense measurements, I could use an INA219 bi-directional current sense module – this way I could monitor the current IN and current OUT of the battery pack. As the IAN219 is a I2C device, I could have 3 of them on the same I2C bus, thus freeing up the 3 Analogue input pins on the Arduino. As we can set the address on each of these devices, it should be fairly easy to identify each device on the bus.

As the INA219’s also measure high side voltage, we now have the power measurement. It makes it a simple choice for this application. These are available as modules which can be plugged into a breadboard.

Temperature of Solar Panels

The temperature sensor could be a Dallas DS18B20 digital thermometer as I could wire a few of these on the same bus for different temperature measurements around the system.

Windspeed (Pulse input? Not sure at the moment).

Pulse input is simple to measure, as we just record the number of pulses within a time interval. Most wind speed sensors will provide a calibration value of the wind speed to the number of pulses per minute.

Rainfall (Digital Pulse Input)
Tipping Bucket Rain Gauge (Click on image)

Rainfall is fairly simple, as most rainfall gauges will tell you how many ml of rain fell per pulse output. Some of the cheap eBay ones have a value of 1 to 0.4ml per pulse. This makes it fairly simple to multiply up the number of pulses per interval to work out the amount of rain that fell.

Output Signals

We have looked at the sensor inputs, now lets looks at various outputs. We could have an LCD screen that shows the various results and information. If it had a backlight that we could switch on /off, it would be easier to read. Then when the backlight is not in use, we would be saving power, letting the system run for longer on the batteries.

If we had an LCD screen it would be nice to have a few buttons to navigate a menu to view results. This of course would add more inputs to the requirements list. If we had four buttons, Up, Down, Select & Exit, this should be enough to navigate through the various menus.

We may have an indicator or two to let us know how things are getting on, without having to look at the display.


Going off grid?

Setting up power to my workshop is proving to be an ongoing project for me. Where possible I want to be off grid generating my own power. Solar and wind both spring to mind – wind for the days when the weather is poor and no solar energy can be collected and solar for the days where it is possible. Given that I live in Ireland and the weather is not the best for solar power generation, it’s worth a try, just to see how much free energy (I use the word free very loosely) can be stored.

This brings me on to the storage of the energy – batteries. Some research is required into the types of batteries to use as this is not something I have tried before. I purchased a basic PWM Solar Charge Controller from eBay and is designed for lead acid batteries. As a first step I want to try to set this system up and monitor the changing/discharging of the battery over a period of time.  I have a couple of 12V6AH Sealed Lead Acid Batteries, that I removed from an old UPS, which I can connect to the Solar Charge Controller.  I plan to introduce a 12v and maybe later a 24V circuit into the workshop for low voltage system, such as the Retro Computer Project.

Retro computer build – what should it do?

What should this retro computer do and how should it benefit me on a daily basis? That’s the question! Well…I will look at porting a version of Basic to the system. That will provide me with a programming language that I will be able to use to develop the application. What if the system also monitors the temperature, humidity, solar radiation and rainfall from the environment in and around my workshop?

By designing the system to be ultra low power while operating, it should have the ability to go asleep when the workshop is powered down, only waking up at specific intervals, to record the necessary signals, save the data and go back to sleep.

Power requirements should be very simple – a small solar panel charging a battery that the unit will run off.

It would be nice to have some form of display. Display controllers drain power so it will be best to keep the system power consumption as low as possible.

After checking stock, I have found some old HD63x0x micro’s that will form the basis for this project. These micro’s have some onboard peripherals that will help when trying to connect to the outside world. The most important component that I see is the on-board UART, which will allow for RS232 communications to a PC.

While it would be fantastic to have a system that records this information, what if I want the system to do something totally different in the future – having one PCB which is the computer core and another which is the interface – some form of stackable system like the PC104 systems that exists?  I will start on making the SBC, (Single Board Computer) and then I’ll focus on the interface board later. At the same time I’ll need to think about how the interface board will work and how to connect other interface boards…

Having a separate interface board is making me think about having other boards attached as well, like a floppy drive controller, to let the system connect to a 3.5″ floppy drive (just because I have a few of them lying about in the workshop). What about a video display board? I know that this wouldn’t fit into my thoughts about low power, but if the system is modular, I could make up a system that is low power for the data logging solution and another system as the desktop retro computer (all from the same technology). Then I will look to see if I can get them to talk to each other, to my PC, or my Mac.

Retro computer build – where to start?

Have been thinking over the idea of building a retro computer that uses technology from my early computer years. Nowadays I design systems based on modern micro controllers, but the old micro’s hold some nostalgia for me.

So what to build and how should I build it?

My first thought was to use the 6502 processor or the Z80 processor, but so many other bloggers and Youtube channels have built retro computers around these CPU’s. I was thinking about one of my favourite computers from the late 80’s – the Epson HX-20, the first true portable computer – battery powered that lasted up to 40 hours, yes, 40 hours. It’s mad to think that almost 30 years ago we got 40hrs on a computer and todays laptops find it hard to get a day.

This little machine has a built in printer which has been very handy for printing results in the field. It also has a micro-cassette drive, which allows the loading and saving of both programs and data. I used one of these machines between 1985 and 1993, while working in my Dad’s company. We provided loggers to companies and semi-state authorities.

If I decided to build such a device, what could I use it for? Could I make it in such a way that it would be functional and able to complete some meaningful tasks for me? Of course I could use an Arduino or a raspberry Pi, but where would the retro nostalgia be in that.

The Epson HX-20 uses an Hitachi low power CMOS CPU – the HD6301. This chip is a CMOS version of the Motorola 6800 family of IC’s, so maybe this could be the starting point?…

This project will be a work in progress, as I trial different ideas to find a solution that ticks the boxes that I’m interested in. A bit self indulgent I know, but hey, its my project.

My plan is to build something that’s as reliable as an HX-20 but actually better than one?