After reading one of the complaints against MWS it dawned on me that both sides were talking past each other and missing a solution. The complaintant stated that his 300 watt AirX did better than a "1600 watt" storebought mill and the MWS reply failed to address the issue.
The AirX has a built-in MPPT. That's why they hum
. The store bought mill has no MPPT, but in a typical grid-tie, the inverter performs that function. With solar you can go direct to batteries, but that is not as good as having an MPPT if you can afford it.
The homebrew mills here don't need an MPPT necessarily, because the number of coils, air gap, wire sizes and delta vs. wye wiring out act to match the mill impedance to the battery bank. Trial and error has led to the design of "self-regulating" power transfer in homebrew mills. The need for a dump load means you are doing it right. You have power to spare.
Since people don't typically make their own solar panels, and most commercial panels are designed to be grid tied, a solar to battery system needs help extracting the max power from the panels. In an audio system, impedance matching isn't needed if you use mosfets, what you want is maximum
voltage transfer. Older audio systems used transformers to match impedance and therefore maximum
power transfer.
Maximizing voltage transfer in a solar to battery system would not be a good idea. The batteries and connected equipment have a narrow range of safe but usable voltage. An alternator charges a battery quickly because it forces the maxmum safe voltage on the battery.
So the best return on a solar to battery system means matching impedances to maximize power transfer. Here is where I think many MPPT's need improvement. I opened my BZ and discovered the panel negative and battery negative are directly wired together. That's probably common, but it means that impedance matching is probably impossible given that batteries are not purely capacitative and solar cells are semi-conductors whose impedance varies with light and temperature.
The fastest charging is constant voltage (with temperature compensation for the sake of the battery). It would seem to me the best way to go solar to battery would be to have the solar connected to a boost transformer and HV capacitor array that would fill the caps and then switch them over one at a time to a separate buck transformer that would force constant voltage onto the battery until the cap was drained and switch to the next full cap. The battery side wouldn't need to be steady dc charging, nor would this be desirable. Pulse-width modulation would probably work better and would ring the battery to break down sulfation.
If all the caps in the array get full and the battery gets full, the MPPT would simply idle until a cap was drained and available.
Does this sound doable?
