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Need help for alternator design to a Lenz2
By MACM, Section Mechanical Posted on Wed Dec 26, 2007 at 08:48:42 PM MST
How could a direct-driven low rpm alternator for a Lenz2 look like?

Hi All
Im working on a Lenz2. The wingspan is 3 meters tall, 1 meter in diameter. That should poss. produce ~ 340 watt 8 m/s at 120 rpm (If Ed Lenz is right - im sure he is!). I want to build a directdriven alternator and this is offcourse the troubleling part. I know that this is not an optimal solution and many thinks it would be better to gear the alternator, but I want to give it a try.
I read throug the whole board (or so it feels), but havent found any descriptions of a low rpm alternator for small turbines. It seems like the main problem for the VAWT now (after Ed cracket the main upstickle) is making a low rpm alternator match the turbine.
Alternator goals:

cut-in 5 m/s - 75 rpm
most effective at 8 m/s - 120 rpm - 340 watt
cuts out at 15 m/s - 230 rpm - ~ 700 watts or more
IF an alternator was to be made for this Lenz2, without regard of price of magnets, what would it look like(specs)?
Regards
Mikkel - Gotland, sweden.

Need help for alternator design to a Lenz2 | 6 comments (6 topical)

Re: Need help for alternator design to a Lenz2 (3.00 / 0) (#1)
by windstuffnow on Wed Dec 26, 2007 at 04:33:57 PM MST

A 12 inch diameter dual rotor with 16 poles per disc, 12 coils single layer, 4 coils per phase for a 12 volt set up would need 58 turns per coil to cut in at 75 rpm. In order to achieve the output you would need a minimum of 14awg wire or equivilant but 13 or even 12 would be better. For 24 volt you would double the turns and use 16awg and for 48volt double the turns of the 24 volt and use 18awg although you might be able to get away with 19 or even 20.

I calculated the outcome using my wedge magnets as a base.

.
Have Fun! Windstuff Ed

Re: Need help for alternator design to a Lenz2 (3.00 / 0) (#2)
by MACM on Wed Dec 26, 2007 at 06:15:58 PM MST

Allright - I thought it had to be bigger in diameter.

How wide can the airgap be (magnet to magnet)?

(thank for a super(and fast) reply)

//Mikkel

[ Parent ]

Re: Need help for alternator design to a Lenz2 (3.00 / 0) (#3)
by windstuffnow on Wed Dec 26, 2007 at 08:01:59 PM MST

No more than 5/8 inch ( 16 mm ) so your stator can be 1/2" thick ( 13 mm ).

.
Have Fun! Windstuff Ed
[ Parent ]

Re: Need help for alternator design to a Lenz2 (3.00 / 0) (#4)
by hvirtane on Thu Dec 27, 2007 at 03:26:45 AM MST

to cut in at 75 rpm

What is planned TSR (and cut in wind speed) then?

- Hannu

[ Parent ]

Re: Need help for alternator design to a Lenz2 (3.00 / 0) (#5)
by MACM on Thu Dec 27, 2007 at 05:37:22 AM MST

Ed says 0.8 TSR is the best - 1 diameter rotor @ 5 m/s, 0,8 TSR is ~75 rpm´s.
5 m/s cut-in should work for me - it would be fun with a lower cut-in, but there is not much power there. 5-15 m/s is also a commen in scandinavia (just now its blowing ~8 m/s SW at ground level).

//Mikkel

[ Parent ]

Re: Need help for alternator design to a Lenz2 (3.00 / 0) (#6)
by hvirtane on Sat Dec 29, 2007 at 03:57:02 AM MST

Thank you a lot for the specifications.

It would be really nice to hear more about your machine. Especially about the measured performance later.

Your place sounds to be really windy. I'm living in the middle of Finland and here it is seldom as windy as you are telling about your place to be common.

I know a man, who has done experiments with a quite similar machine, but seemed to know nothing about Ed's machines and plans. I heard that he built a new machine with similar dimensions as yours, his first one was only one meter tall. He is living far from me, and I cannot visit him just now. My plan is to make a trip to his place later.

- Hannu

Need help for alternator design to a Lenz2 | 6 comments (6 topical)

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