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building a dual rotor
By redneck power co, Section Mechanical Posted on Wed Jul 16th, 2008 at 12:05:31 AM MST
Question about construction

We are building a dual rotor 24 magnets, 9 coils number 14 wire. I dont understand why you need two wires wraped 36 times for a 12 volt machine? Why not 72 wraps with one wire? I just want to fully understand what it is that I'm doing before I do it. And also why are the magnets on the second plate not staggered?

building a dual rotor | 8 comments (8 topical, 0 editorial)

Re: building a dual rotor (3.00 / 0) (#1)
by vawtman (vawtman(at)charter(dot)net) on Tue Jul 15th, 2008 at 06:57:36 PM MST
(User Info)

You seem to be following plans so don't deviate from them until you get gutsy from more experience.
The mags on an aircore(dual rotor) don't need to be skewed(staggered) cause there's no stationary steel involved within the gap that could cog it.

Mark

Re: building a dual rotor (3.00 / 0) (#2)
by jonas302 on Tue Jul 15th, 2008 at 07:16:46 PM MST
(User Info)

The two wraps or two in hand as they call it is to carry the amperage not to increase the # of turns as they are hooked up in parallel basically it would equal your 36 turns of wire twice the size that they specify but the really thick wire would be hard to wind and probably more expensive

heres a great build page if you haven't seen it http://otherpower.com/turbineplans.html

Re: building a dual rotor (3.00 / 0) (#3)
by TheCasualTraveler (a.miklos@yahoo.com) on Tue Jul 15th, 2008 at 07:52:50 PM MST
(User Info) http://thecasualtraveler.com/wind.htm

I asked about two in hand before. Flux gave me this,

""The number of turns decides the voltage you get. The size of wire determines the resistance and is one factor in determining the current you get.

Normally you would choose the thickest wire that will go into the space and give the chosen number of turns. Sometimes the ideal wire size is too thick, either to handle physically or with these alternators you run the risk of eddy loss in very thick wires.

In these cases you can make up the same cross sectional area of copper by using more than one strand of smaller wire and it behaves as if you used the thicker wire but without the problems mentioned. There is no actual gain or advantage except where I have mentioned about the limitations of very thick wire.

Sometimes it is done for other convenience reasons. If you ideally needed #12 but you had a reel of #15 then using 2 in hand #15 would do exactly the same job.""

Here is the whole thread,

http://www.fieldlines.com/story/2008/1/4/2848/43881
Andy

Re: building a dual rotor (3.00 / 0) (#4)
by Ungrounded Lightning Rod on Tue Jul 15th, 2008 at 08:52:09 PM MST
(User Info)

So 72 wraps with one wire would give you twice the voltage and (at the same percentage of power lost to resistive heating) half the current. You'd have a 24 volt machine with the same wattage output as the 12 volt machine you're trying to build.

[ Parent ]

Re: building a dual rotor (3.00 / 0) (#6)
by boB on Wed Jul 16th, 2008 at 12:26:10 AM MST
(User Info) http://bob.gudgel.org

Yes, you'd be able to run it as a 24 Volt machine if you ever wanted to change, or,
if the wire run is long and you get a wind MPPT controller, you might get lower
losses running it as a 24V machine and let that buck converter help reduce your
wire losses.

boB

[ Parent ]

Re: building a dual rotor (3.00 / 0) (#5)
by electronbaby (roy<at>windsine.org) on Tue Jul 15th, 2008 at 09:29:53 PM MST
(User Info) http://www.windsine.org

not to complicate things anymore, but 12v dual rotor alternators can be made to work well, but they are terribly lossy due to the low voltage and presumably, high current. You will find this out as you gain more experience.

I also suggest you stick to the plans you are probably following, until you get a little more comfortable with the concepts involved.

Please share your photos of your build. we would love to see them.

good luck. :-)
Have Fun!! RoyR KB2UHF

Re: building a dual rotor (3.00 / 0) (#7)
by Ungrounded Lightning Rod on Wed Jul 16th, 2008 at 03:28:58 PM MST
(User Info)

However the losses are in the wiring from it, not inside the alternator itself. If you double your current by going to half the voltage, you need to either double the thickness of your wiring from the alternator to the battery shed or suffer a quadrupling of the line losses.

For a given cross-section of copper in the alternator you get a given amount of power and a given percentage of heating loss, regardless of whether the wire is divided as many turns of thin wire (high voltage, low current) or fewer turns of thicker wire (lower voltage, higher current).

(Again, this is an approximation - though a very close one: When the wire gets thick enough the eddy current losses increase enough to become non-trivial, which makes you deviate slightly from the all-vlotages-are-equally-efficient-inside-the-alternator ideal. Winding N-in-hand when dropping voltage and raising current by a factor of N from a single-strand winding, in order to keep the wire size constant, eliminates this slight deviation.)

[ Parent ]

Re: building a dual rotor (3.00 / 0) (#8)
by Ungrounded Lightning Rod on Wed Jul 16th, 2008 at 03:32:12 PM MST
(User Info)

For a given cross-section of copper in the alternator you get a given amount of power and a given percentage of heating loss,

Make that "... a given percentage of heating loss AT THAT POWER LEVEL ...". Resistive heating loss goes up with the SQUARE of the current, so different power levels have different percentages of losses.

[ Parent ]

building a dual rotor | 8 comments (8 topical, 0 editorial)

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