car alternator "turn down"

[john j]

Im building this Rahai type vawt. And I want to use a car type alternator for the first tests. If I could put a sort of resistor between wt and battery, I could use the alternator from any car, and maybe even get a sort of metering of the power from the wt. Any ideas? my project: http://thebackshed.com/Windmill/FORUM1/forum_posts.asp?TID=980&PN=1

[finnsawyer]

What is the expected cut-in RPM of the VAWT?  A car alternator needs 800 to 1,000 RPM to reach cut-in, and that would be with the field coil fully energized (4 amps from 12 volts).  You can get the field current from a separate battery through a rheostat (resistor) for tests, but how are you going to spin the alternator fast enough?  You might be better off getting a small high voltage (90 volt?) dc motor and use that for the tests.  Might still need some gearing up, though.

[john j]

I thought I would gear up the alternator to reach 1000+ rpm. Simply a v-belt on the rim you see in the pics. If things work, the next step would be to make my own PM generator. So this would be for testing only. Could you   tell a bit more about this rheostat thing? Any sizes, numbers, sketch etc? Thanks, j

[wooferhound]

Lot's of information about car alternators as power generators on this page with it's links.

http://www.fieldlines.com/story/2003/11/4/12921/5571

 

[john j]

http://www.fieldlines.com/story/2003/8/4/22368/12185

Woofer, this one didnt work. I thought of simply putting a resistor between alternator  and battery. Thus making life easier for my mill.

As you can read I am not into electric stuff. Anyways, some of the most interesting stuff was made by people not knowing it wouldnt work.......

[finnsawyer]

Try Googling "Rheostat".  I just did and got 500,000+ hits.

[john j]

thanks. This is not easy. Found this about pm in car alternator; http://www.windstuffnow.com/main/gm_alt_mod.htm

Nothing about rheostat so far. I ll read on....

[john j]

OK, I think I found it, thanks.

http://www.fieldlines.com/story/2008/4/3/14518/94939

[tecker]

If you can get the rpm up you just hit the rotor field once and your good.

[tecker]

Here's hiker solution works good.

http://www.fieldlines.com/story/2007/9/1/7921/49961

[tecker]

http://www.fieldlines.com/story/2007/7/31/93955/8934

[john j]

thanks Tecker. This is exactly what I was hoping for.