Looking at your situation, it's my opinion that you'd be much better off with a small, fast turning 75-100 watt HAWT to get what you want out of the low wind speed. A properly designed little HAWT will start spinning with the slightest breeze and can be designed to easily reach cut-in and charge batteries with a few watts in low wind speeds that you're talking about.
The thing to remember is that rpm's is a good thing when you're driving generators because it allows reduction of the amount of wire you need in the generator (and hence, resistance) to make useful power. Frankly, the VAWT is just not the design to use for that.
I came up against the same thing that you're battling with my VAWT project and that's why I shelved it for awhile. VAWT's, despite the claims, are not as efficient as HAWT's. They're not as practical as HAWT's. And they're bigger and require a stronger tower than HAWT's.
So my suggestion is, if you've never actually built a wind turbine before, start with a HAWT to get your feet wet and go from there. Most of the work in building a HAWT will be on the generator. The rest of it is pretty simple stuff and you can even make a set of cheap PVC blades (under 2' or so) to get started, then work your way up from there.
The bottom line is that a little HAWT can spin hellacious rpm's in moderate wind which makes building the generator simple. You'll learn a lot from starting with a simpler project and you'll get more useful power of a little HAWT. If you're set on building a VAWT you're going to have to eventually reach the realization that it takes a pretty big contraption to make any useful power at all and it takes just about gale force winds to make them really perform.
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Chris