I presume you're talking about Hugh's circuits here?
http://www.scoraigwind.com/circuits/index.htm
His tacho circuit is essentially the same as mine, except he doesn't include the meter.
His op-amp comparator circuit is also essentially the same as mine; except his output goes to a triac via an opto-coupler.
My circuit is more complex, yes, but it gives auto/manual control over star/delta, and intelligent indication of what's happening. The leds flash when in manual mode. In reality, it's only one 14 pin cmos chip, which costs about a dollar.
By switching it to manual, and locking it in one mode, you can then get current vs rpm data. Once you've done this in both modes, you can then choose a suitable cross-over frequency, and adjust the trim-pot to suit.
Switching AC at the zero crossing point is preferable in 2 situations.
First, when you have a large reactive load, and switching causes lots of arcing to relay contacts, or stresses the solid-state devices doing the switching and arc protection.
Second, where you are switching on every cycle, and the switching noise creates RF hash (interferes with radio & TV.)
I think, switching 3 phase from star to delta, using zero crossing, if not completely impossible, is certainly making life more difficult. Only one of the 3 phases is ever at zero at any given point in time. Questionable advantages when we're only talking power levels, in most cases, of less than a kilowatt at full power. So the power at the switch-over point is only a couple of hundred watts. And, it's not going to be switching 60 times a second, 24/7, either.
It is possible to use a tacho circuit driving an op-amp comparator to short out the windings above a certain rpm. I'd probably want it latching, and raising some sort of alarm; preferably a flashing led, which remains active until the latch is reset, and audio indication (think sonalert) with it's own "silence" switch. Whether the alternator comes to a screaching stop, or just keeps spinning & smokes, depends on the alternator, and how much resistance between it & the relay contacts. So you'd probably want the actual relay at the top of the mast. More wiring, and a bigger pain if things go wrong. For me, the less gear on top of that mast, the better.
A properly designed furling system is, to me, much simpler and inherently more reliable.
I have seen people use a manual switch at the base of their tower, to short out the windings while doing maintenance, or if extreme weather is coming. But I think the idea is to shut it down "before" the weather hits.
Amanda
