Friday, March 17, 2017

Geeky Graph

Please excuse the geekiness of this post but I think that this is kind of interesting. Since I've had the test solar panel up, there has not really been a stretch of clear, sunny days like we've had over the last week. Whenever I checked the status of the Tristar solar controller, I never saw it go into "float", i.e. very low current and a maintenance voltage to keep the battery charged. For the temperature of the battery bank (8°C), the controller was varying the current to maintain the battery bank voltage at 13.93 volts using the "sense" wire that I had installed earlier this week. The sense wire is a 22 awg pair that go from the "sense" terminals to the main positive and negative terminals of the bank so the controller can get an accurate voltage of the battery bank unaffected by current that may be running through the cables. Another great feature of the TS-45 charge controller.

This graph is still from the data logged through the serial connection to the Windows 10 tablet as I hadn't even started messing with the Raspberry Pi to log the data. On the graph I labeled the absorption and float portions of the graph. The array voltage is orange and that is what drops to almost zero at night and goes up over 20 volts when the controller isn't needing all of the power that could be produced. The lower grey line is the current going to the battery bank and the blue line is the battery bank voltage measured on the "sense" wire.

In this annotated graph from last Sunday, we can see the bulk charging where the the controller never leaves the bulk charging mode. You can tell as the array voltage and the battery voltage track each other. The peak current from this panel is almost 8 amps. Pretty impressive performance as the panel is rated at Isc (short circuit current) of 8.02 amps. 

6 comments:

  1. Yep, too geeky for me. Made my eyes glaze over. ­čśŐ

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    1. I'm afraid that I find stuff like this interesting. Working on the Pi version requires me to start learning Python. I've managed to avoid it all these years...

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  2. Am I the only one thinking the thumbnails look like a cross section of the Panama Canal?

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    1. Hmm, so I'm not the only one that thought of that...

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  3. What sort of display will the Pi drive? And, it looks like the tablet already does a great job, so why change things at all?

    I'm impressed with your setup for sure!

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    1. The Raspberry Pi runs on less than 3 watts of power and I can run it right off 12v as it is powered through a micro USB port. The Pi has an hdmi port and will do 1080P but I'll be running this as a headless linux host (no display) and the interface to the solar info will be through the web server running right on the Pi. Management of the Pi will be through SSH. The version 3 board has built in hdmi, 100BaseT, WiFi, Bluetooth, 4 USB ports and a quad core CPU. A pretty decent computer for $35. Plus, on the Pi, I can automate the whole data collection and presentation process.

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