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I haven't mastered inductors

A project log for MPPT for low voltage solar harvesting

Microcontrollers + caps = MPPT in the time domain?

Simon MerrettSimon Merrett 09/23/2019 at 14:300 Comments

A wonderful aspect of Hackaday.io is the way you can bump into kindred spirits that live miles away and you would never have come across were it not for this community. The most recent example of this kind of blessing was when @crun volunteered to join this project. I accepted immediately and benefited from several long whatsapp chats and images of pencil sketches. Although we got sidetracked while chatting into a fascinating array of tanget-topics, @crun explained how the capacitor technique that spawned this project was generally flawed with respect to the alternative - inductor boost circuits. 

As the concept became clearer to me, I could see there are significant parallels between the basic switching boost converter we were discussing and the inductor-based LED drivers used in #TritiLED and #Yapolamp. The fascinating (to me) part was that  @crun  had managed to use microcontrollers (PICs) to omit some of the external components of the switching boost converter, namely the diode and FET. I'm not going to go into the idea further in this log because I just wanted to confess that after several days of trying, I have failed to make a switching boost converter that shows potential for being well matched with my supercapacitor energy storage scheme.

The main reasons I think are behind this are the need to carefully judge when it is acceptable to draw power with the uC/inductor. If you switch on too frequently or for too long, you will deplete the potential across the photovoltaic panel/buffer capacitor to the extent that it can no longer provide useful current to the inductor and scuppering your plans to shove the resulting energy over the diode and into the supercapacitor. I have tried a range of pulse durations, pauses and components (inductor from 0.68mH to 6.8mH) and so far I just can't seem to get a boosted voltage worth writing home about. 

I'm not giving up, but I am going to move back over to a purely capacitor-based circuit, while I lick my wounds!

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