Who would like to beta test one of my new voltage regulators?

Progress, finally. Thanks to Jim Kueneman, who checked with an alternator simulation and realized the circuit I had copied off the stock type regulator could be very finicky depending on capacitor size and some quirks of the alternator. So I made some changes so that the regulator acts more like a Schmidt trigger and instead of having a minimum time between switching the field off and on, it targets holding the voltage in between a minimum and maximum value. Here's a data log from the onboard EFI when testing my new regulator and a stock-replacement regulator - the sampling is at around 20 Hz, so it won't catch abrupt spikes, but it shows the new regulator (left) is holding voltage as well at that sampling rate as the old one (right).

So what comes next? In about this order:

regulator graph annotated.png