MPPT Solar and Wind Power Boost Charge Controller
From Open Circuits
This circuit matches a low voltage solar or wind turbine input to a higher voltage battery. An analogue circuit will measure incoming current and voltage inputs to set the maximum power point tracking (MPPT) and boost the output voltage up to charge a higher, or equal voltage, battery. Input voltage range: 9v through 60v. Output battery voltages: 9v through 60v. MPPT will work only if the battery is higher than the input source. Otherwise, the circuit will act like a direct connection, source to output. It is based on the LTC3703 boost converter IC.
Here is the basis of the circuit idea and the testing and calibration videos: (Edit Sep 2013). The videos document my work. Newcomers to MPPT will be helped if you read this and understand that the circuit can pull a wide range of watts from an input. It is the TL081 calibration which sets the loading. A large turbine could be loaded more than a small turbine. Once set, then the V=I is my way of saying maximum power is along that fixed line ratio as wind speed varies and volts varies. It is my idea to not use sampling and MPPT seeking. Instead do impedance matching V/I=R. I mention the danger of using a heavy available amps like a large input battery while setting up the calibration because you could burn up the circuit. I prefer wall adapters or use input fuses.)
I calibrated the MPPT boost board and I had success with input V/I ratio held constant, when changing the input voltage. I boosted 12.5v to charge a 58.6v battery and 26v was boosted to charge a 58.6v battery. Current, at 12.5v, was about half, as was expected.
This is a voltage boost circuit to raise my low voltage furnace fan motor on my wind turbine, to get above and charge my 48v storage battery.
I still have more testing to do. Later, I think I will sell my nine extra boards with one LTC3703 soldered in place, for $59.95US if you want to try the circuit. After they are gone, I might release the board layout diagram, which is critical to success. I burned up a lot of parts with spikes, before succeeding.
It is 9v through 60v MPPT boost to a 48v nominal lead-acid battery. It needs more testing after I attach a wind turbine. Otherwise, it seems to work, so far. How much power can it handle? I am not sure yet. I think 500 watts minimum and maybe 1K watts with more copper over the traces.
This circuit is an analogue computer, when run without a microprocessor. As rpm voltage rises, current is allowed to rise proportionally. The variable loading math is P = I(V-offset) and (V-offset)/I = R (like a fixed resistor load) and I x constant = V. The op amp pegs I equal to V. It is suitable for solar. Wind is a cubed relation, not squared extraction, like this analogue calculation will yield in wind; eg. 2I and 2V = 4P. So, it will likely need the microprocessor for optimizing wind MPPT, but without a microprocessor will be interesting. It will be better than feeding my very high voltage battery, directly because my generator rarely gets above threshold volts, which is 48v to 59v, depending on how full. So it needs a boost converter. It is doing integration math, via the op amp. I added a pin header for optional microprocessor control, which I have not tested, yet.
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