Sunday, January 24, 2016

off grid transfer switch

Off grid solar and wind power has become more urgent, because governments constant hunt after more tax to finance the old fossil energy sociaty structure.

This post i about my 'off grid lite' system, and a smaller but important part in my off grid power system, the load handler. The load handler is a electronic off grid transfer switch that can handle switching and sourcing a huge amount of electricity, with low voltage drop, low head release, and low waist.


I have 5200 watt installed grid tied solar cells, and i like to more than double this to become 100% self-sufficient.

But it is not possible to do that, without going to pay lot of taxes for the energy i need to send to the  grid in the summertime, and draw back in the winter time for a heat pump.

The cost of a off grid system capable to deliver this amount of power is a challenge. Automatic functionality and transfer switching between different sources, is also a hard job to create with low waist energy consumption, and operational stability.


The off grid lite system is made as a scalable and modular system, and in this system the load handler become crucial for operational stability, i a battery, solar and wind driven power plan. The tesla power wall is a upcoming solution, using fronius hybrid inverter from Austria, but the tesla wall have a cost that isen't micro economic scalable. You need a bigger amount of money to get started.

There fore i decided to start with what i have in my garage. Some old laptop batteries, a battery pack from salvaged electric scooter, old diy experimental solar panels, mosfets, din rack enclosure and more.

The 'off grid lite' system was born:
tesla power wall alternative

In the off grid lite system i use several load handlers. The load handler is mosfets used as switch and driven by a micro controller. I use arduino uno to measure off grid system variables and to turn load handler on and of.

The load handler is called 'arduino load handler' and the design is made to fit a DIN rail frame found on thingerverse. The electronic for the off grid lite system consist of several parts, and some can be found om my site, more parts and drawings can be placed here and on my website as the project progress. For now you can find a BMS solution for salvaged labtop batteries and a arduino MPPT charger design whit printed circuit board.

Friday, November 28, 2014

mppt solar charger with arduino and free arduino shield

printlayout til tim nolans mppt lader
This is the RC1 techmind release of the mppt solar power charger with arduino
mmpt lader med arduino
The mppt solar charger shield is opensource and you can use it as you like

Tim nolans original arduino mppt sketch


 Eagle diagram og print layout

Scroll to the end of the post on this site to download schematic and pcb files for eagle: MPPT schematic and pcb eagle files for rc1

Sunday, February 19, 2012

Shortcut protection for power supply

This i the automatic shortcut protection circuit in my dual  rail power supply with 2 x lm338

Schemtaic for the shortcut protection circuit,. This is scheematic for the single rail powersupply, you can just add more  optocouplers in series for dual rail, or even more rails.

Wednesday, February 15, 2012

Saturday, February 11, 2012

Arduino as voltmeter

I made a solardatalogger for few years ago (will publish code latter to this solardatalogger).

In my solardatalogger i used arduino with a ethershield to mesure battery bank voltage with analog input.

The analog input at the arduino board are not protected, and will burn if 20 volt is connected. So i made a overvoltage protecting circuit with a few 1% resistors and a 5 volt zener.

The codesnip below is used to integrate in you own arduino sketch, enjoy ;)
Arduino as Voltmeter

The routine showed in the codesnip collect data from analog pin 5, at 5 volts contains whole 1023, the divide by 2 and converted into 4 digits. The 4 digits plus a decimal point is stored in a string of char with excitement: 05.00 ready to send serial with usb or via ethernet.

A better way to scale the analog input is with the MAP command:

map(value, fromLow, fromHigh, toLow, toHigh)

This command is very flexible. value is converted from 0 to 1023 to 0 to 20000

Then we have a good solid scale, and need only to divide by 1000 to place the decimal point.

In my own solardatalogger project data is sent to a mysql database and it is easy to handle calculations in php instead of the Arduino.

In my EVduino-MS project the voltage value will be converted into  graphic bars on the LCD touch display