This is pointless, the field needs about 40 W to do much so your mini turbine needs to produce at least 40W. If it doesn't and you use it to kick the thing off you need your main turbine to produce 40W before anything goes into your battery.That power doesn't disappear it has to be produced from somewhere.

Let's take a bit of a realistic look at things. A fast 5ft prop could reach 1000 rpm in about 15mph wind.  With a bit of luck it would  probably produce 60W at 15mph so by the time you have supplied the field you would end up with possibly 20W rather than the 60 of a pm alternator. If you have lots of high wind and you only want very little power then you can get something from a car alternator. For most people on a normal lowish wind site it is a very miserable way to get very little.

In the old days we had little luck with car dynamos and their field requirements were less and the cut in speeds lower. Alternators are a step backwards.

If you replace the wound field with permanent magnets then you loose the 40W of wasted field power but you add iron loss and cogging to delay start up and you remove some of the flexibility of the wound field and ease of load matching. It is still a pretty miserable thing but at least it will do something from about 10 mph upwards.

To replace the wound field with permanent magnets is a fair bit of work and a few scrappy magnets aren't going far towards a decent solution so in the end the whole thing becomes a lot of work for something with mediocre results. If you want to go that way then fine, you will have fun and learn a lot and you will find out the hard way what everyone else has been saying about car alternators for years.