I Recently built a home brew pma wind gen. but with the winds in my area on a normal/average day its putting out 2.5-6 volts dc my quistion is could i build a step up boost convertor to up that voltage/amps to charge 12 volt batteries?
i have also seen the gen put out 26 volts on very windy days
What you need is a buck-boost converter. As it's name implies, it can both "buck" the voltage down, or "boost" a voltage up. This will allow you to handle both the low and high voltage wind conditions.
There is a TON of information all over the internet about them. Dedicated ICs, lots of schematics, etc. They are one of the most common DC-DC converters out there.
Unfortunately it looks like you have selected a winding turns to wire diameter for a low voltage/high(er) current alternator.
The wire gauge determines the maximum amperage allowed. The number of turns determine how much voltage is generated. Obviously for a given alternator physical size you can't put more turns without using smaller gauge wire.
The V-I curve for a permanent magnet alternator is a complicated relationship between rpm's/torque and electrical load. You generally would like to get a usable voltage at relatively light wind with a relatively light load. The load regulator then becomes a matter of keeping voltage up by adjusting the load on the alternator. A buck-only switcher regulator is the simplest and more efficient then a boost or buck-boost design.
2.5 v. doesn't give you much to work with.
Stating only voltages does really say too much. When you say you have seen 25 v. on a windy day, how much current was being produced at that 25 v? When you get some reasonable wind do a load current versus voltage profile. If that was open, no load voltage you have a problem.
An old telephone hand-crank ringer generator can produce 200 volts. It just doesn't do it with much output current.
I did 36 windings with two strands of #14
wire the blades are a bit under sized at a dia of 6 foot
I did hook a 1/2" drill to it on the ground abd got 176 volts out of it.
And I have no way to measure the current at this time I have orders an amp meter that hasn't shown up yet.