Random thoughs & next steps

Arduinos are quite good, aren't they?

When I first heard about them and saw the Arduino IDE with it's 'sketches' I had a very brief look and formed an opinion that they were very basic with a very primitive language suitable for starting to teach kids about basic programming techniques with the ability to connect some LEDs and buttons.

After digging into the AtMega specs, the hardware capabilities, SPI, I2C interfaces and the tons of libraries that are out there for the add on boards, all in C or C++, they care certainly a lot more capable that I first thought.

Takes me back to my days playing around with Z80s, 6502s or early Linux and DIY MPEG software.


Well the storage unit is chugging along nicely now, the charge rate is controlled by the free power so it does its best to keep exported power between 50W and 100W with everything else going into the battery. Night time the three inverters are switched in and out according to demand.

A couple of odd things I've noticed so far:-

* The 2.2" TFT display on the Arduino has a command that rotates the output in 90 degree steps. Occasionally the output is rotated by 90 degrees by itself. I think it's just noise on the data lines going to it, and a proper PCB or shielded cables will sort it.

* The LiPo / LiFEPo4 charger has a current control knob on the front which lets you set the current in the CC stage between 6A and 100A. I struck a home run as this is a simple 5V feed into the charger control PCB! So a nice direct connection from the filtered PWM output from the Arduino to the charger input. One thing that is a little annoying is the charger is a one cycle charger - if it's left connected to a charged battery it doesn't detect if the battery needs topping up and turns it self back on. It'll charge it up and then sit there until the mains power is cycled. Also if the charge rate is set to zero, it sets charger current to 0A causing the charger to think the battery is fully charged. Got round this by using an absolute minimum charger control value that equals ~7.5A so the charger will only think the battery is full when it actually is.

* The Frontius grid inverter cuts out when it's running at high power. In bright sunshine at midday it can run for a minute and then cut out and then take maybe 3~4 minutes before it kicks back in again. Not good. Must call the installer out.

I still have no way of measuring how much charge is in the battery. I know if it's full or flat, but from 20% to 85% charge the battery voltage is virtually constant.

Will use an opamp to boost the voltage across the current shunt which will allow me to work out that info.

I also want to measure the efficiency of the sytem, and to this end I have another current sensor and enough spare channels and parts to add another power sensor which will measure the power going to/from the charger / inverters which will tell me the loss in the charger / battery / inverters. I suspect it'll be around 50%!

Lastly this coming week I'll be leaving the system on and recording the electricity meter readings, and then turn it off next week and record the readings again. Well, I want to do it on two weeks with approximately the same weather, so it may not be those weeks, but close together.