Thursday, 17 April 2014

BMPPT Solar Charger (2)

Rightio, that peaking current that I previously reported? Well, that was me being un-educated that inductor in the 'fly-back mode' requires air-gap. Without the air-gap, my toroidal inductor was very quick went in to saturation and giving me much smaller inductance. I've found an excellent article here explaining it. Thanks to Dremmel, I simply cut air-gap cowboy style to my toroidal inductor.

That simple problem, paragraph above, took me literally hundreds of hours of troubleshooting, and couple of re-soldering activities due to burnt PCB tracks and components. Ouch...

But, I'm happy to report, by simply adding air-gap, now my BMPPT charger works properly. It actually works better than I anticipated (good problem to have). It tracks my solar panel very well up-to 25W output (during test day, it was very cloudy, couldn't test it all the way to the rated 80W). Efficiency during test also OK-ish (> 87%), even to include the Arduino board power consumption.

So, here it is the final schematic. Input capacitor (C1), and smooting capacitor (C3) were added after various tests:

Do note that exact component values are not critical. These components were selected because I was trying to re-use components that I already have. Final board photo, not looking that pretty:

Oh, the code for the Arduino Uno is here.

Charging current and final trickle voltage is all adjustable through software. The code linked above is to charge my 36V 11.6Ah lithium battery, i.e. charging stops at 42V. I didn't put current limit in the software.

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