How To: Device that stops back feeding the Grid from wind/solar

I’ve read a few Internet posts regarding people who want to self install Solar or Wind energy systems and would prefer to not power the Grid or give free electricity to their energy company. These installations may be small and not wish to invest in upgrading their meter to support back feeding the Grid.

I did a quick search and didn’t find anything simple that would do the job. Looking for a small device that can be installed in the meter box or at the entry point to a small setup, ie workshop with Solar panels and Grid* inverter then 240V equipment connected to inverter, this would allow a personal workshop to pull power from Solar when available and from GRID when not available or using larger tools.

* ALL solar setups that connects to Mains must use a specialized GRID inverter to sync the AC waveform to the GRID. So that the inverter boosts or amplifies the AC Wave. Connecting a normal Inverted to AC Mains will immediately pop the fuse or much worse.

This is where DIODES come in. A diode isn’t to convert AC to DC, while the correct design of 4 diodes will convert AC into wobbly DC, that doesn’t mean that all Diodes will do the same.

AC is a signwave that is the exact replication of a motor turning, as this is how it is generated in very large installations. The AC Wires swap every 1/50 of a second, as if someone was swapping a battery around every 1/50 of a second.

With a Diode we can direct current flow to only 1 direction. With DC, stopping a charging port from also discharging back to the charger is easy, 1 single Diode will do the job, however with AC, we need to do almost the same as the GRID Inverter, the Diodes need to swap as the AC Waveform swaps, every 1/50 of a second, at Zero Volts, the Diodes must swap to follow the current, or in our case, stop the current from flowing in a certain direction.

Below is a quick Schematic of the diodes and switches. The switch wouldn’t be a manual switch, as below, a semiconductor circuit would be used with a microcontroller to monitor the AC Waveform and swap as required.

Screen Shot 2016-02-21 at 1.20.28 PM

The Diodes and electronic switches need to be sized for the expected current, any microcontroller on todays market would do the processing without issue. Expected cost to be around $150 or less for those with enough parts laying around.

At some stage in the future, I intend to build the above and demonstrate for a small 200W Solar install and mini Grid inverter, the ones on ebay that plug into the power. Showing a Fridge running from Solar and when the fridge is off, no current feeding back into the grid. – David Robinson


How To: Auto Convert iPhone Images to BW and shrink for receipts

I’ve been taking pictures of receipts with my iPhone and needed a very simple system to convert the 1MB+ JPEG images to Greyscale and downsize to something smaller than 2448 x 3264.

The answer was a combination of ImageMagick and MacOS X Automator.


  • Make sure Xcode is installed through AppStore. (Free)
  • open a terminal, run
    xcode-select --install
  • Agree to Xcode license in Terminal: sudo xcodebuild -license
    sudo xcodebuild -license
  • and select MacPorts for your version of MacOS X.
  • Download and run the installer.
  • Back to terminal and run the below (will take a while to download all dependancies.)
    sudo port install ImageMagick
  • Now we can start to play. Open Automator (comes with Mac OS X)
  • File -> New

Follow Image below:


Add the below code:

for f in "$@"
/opt/local/bin/convert "$f" -colorspace Gray -resize 640 "$f"

Now we can drag any images onto the and they will be converted from 1.7MB RGB to 70-100KB Greyscale and look great.