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Gizmo's Picaxe based Windmill Controller/Charger. Page 1 | 2

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The original charger described on the previous page has worked faithfully for the last few years.

Recently I needed to set up a controller at a friends place to monitor a prototype windmill. I wanted to use my trusty old Picaxe controller, and decided to rewrite the software to add a few functions.

First up I modified the circuit to run as a dump controller instead of a bypass controller. This meant a few minor changes to the circuit, basically just reconnecting the terminals at the back of the unit. And I changed the MOSFET gate drive resistors to a lower value, 22ohm for the drive and 15k as the pull up resistor. This should mean the MOSFETs will run cooler.

I also fitted a new display panel. Its a LCD from a old 17inch monitor I scrapped recently, 20X2 characters and has a nice green back light.

Recently I scorred some nice current transducers, so used one to monitor the battery amps instead of my home made transducer.

I also added a fan to the back of the case. The fan is connected across one of the outputs, so cuts in when its needed most to cool the mosfets. I dont think the fan is needed, the mosfets dont get that hot, but I figured it wouldn't hurt to blow some cool air around the case. Its a dump controller anyway, so might as well dump some power into a fan.

And lastly I fitted the 7805 regulator to a big heat sink, it was running HOT!

The new software code is very different to the old code, its almost a complete rewrite. The big difference is the use of peeks and pokes to free up variables. To calculate watts I needed to use WORDS ( 0-65536 ) instead of BYTES ( 0-256 ), so I had to free up as much variable space as possible. By use pokes and peeks as temporary storage, I could free up the WORD variables for the math functions.


The software was changed to provide the following features.

Click to see the new circuit

This is the current transducer I used

  1. Increased current resolution. The original controller could read +-12.5 amps in 0.1 amp steps, or 125 amps in 1 amp steps. Now it can read +-50 amps in 0.1 amp steps, or +-500 amps in 1 amp steps.
  2. Added watts reading. Displays the current watt reading. Note, this version of the software doesn't display negative watts ( battery drain).
  3. Added watt peak reading. Displays the peak watts, reset to zero by turning the controller off and on. This is a handy way to see the maximum watts you windmill or solar panel generated.
  4. Added the ability to switch the outputs ( dump loads ) independently. You can set each output to switch at different voltages. You could use this to switch on a water pump, heater, fan etc when the battery is fully charged, and a dump load when the battery is starting to overcharge. You could also use this function as a low battery cut out by connecting your load ( up to 20 amps ) to one output, with the dump load on the outher output.
  5. There is a page in the menu that lets you zero the amps reading. This is handy if you have a stray current that you want to exclude from your display figures.
  6. Added a PicLog friendly serial data stream, so a future version of the Piclog can read and log the data stream from this charger.

The rotary switch at the front of the case works slightly differently than it did in the old version of this charger.

  1. Off is off, the dump load outputs are open circuit. Note, the PicAxe has flash ram so if you turn the charger off and on, it wont loos the output switching voltage settings. When you turn the charger back on, it will reset the peak watts value to zero.
  2. On, or Auto, Regulate. The charger will switch the dump load outputs on and off, independently of eachother, as set in the setup menu.
  3. Forced Charge. Dump loads are open circuit, and wont switch in automatically. The charger will beep every second to remind you that it has been left in a un-regulated condition.
  4. Forced Load. Both dump load outputs on, and wont switch off automatically. Again, the charger will beep every second or so.

Click here to download the new PICAXE code.

Its still ugly in there!

© TheBackShed 2011