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what performance in watts do you see at 100 rpm?
By xymox, Section Mechanical Posted on Thu Sep 8th, 2005 at 01:55:46 PM MST
what performance in watts do you see at 100 rpm?

I am just thinking that we should probably have some sort of a chart that states the size of the rotor and the energy output so we have some metrics that we can try and achieve. There doesn't seem to be anything on here like that. I think it could help people in determining if they have an efficient setup or not so I was thinking that if everybody that knows how many watts they crank out at say 100 rpm (to keep it a somewhat controlled expirament), if they could post it along with there setup details (size, windings, materials used etc). Ah and maybe have a small cash award (or a 12 pack of favorite brew) at the end of the year for the one who can crank out the most.
Just an idea.

what performance in watts do you see at 100 rpm? | 10 comments (10 topical, 0 editorial)

Re: what performance in watts at 100 rpm? (3.00 / 0) (#1)
by johnlm on Thu Sep 8th, 2005 at 09:34:20 AM MST
(User Info)

Xymos,
I think I understand what you are wanting but it is not as simple as just listing a power output at say a given rpm, or a given pmg dimension. There are alot of variables that change the outcome for given dimensions and given rotational speeds. And the 100 RPM point is a pretty low point to start measuring things - not many folks who might have pretty effiecient machines under 12 ft in prop diameter (HAWT) will have much power to report at 100 RPM. Now if you limited everybody to using exactly the same number, type and size of magnets, and let all the remaining variables be whatever one wanted (amount of money spent; prop size and style; wire size and number of turns; dual rotor/single rotor/ laminates / no laminates; increased rpm due to gearing; Hawt; Vawt; tower height; altitude at which it operates; etc) then you might have a good basis to start comparing efficiency of designs for someone to win that case of beer; but getting everybody to start out with the same set of magnets would require some folks dedicated to being in a contest.
In general, once you select the magnets (type and size and quantity) your going to use, and the prop size, you can pretty much estimate how much power you are likely to get if the rest of the machine is reasonably effecient. Some folks have enough experience, or engineering capability to likely give a first pass approximation as to how much power you are likey to be able to get just knowing those two parameters. Possibly what your asking for is a table with that kind of information; but it is a reasonable amount of work for some single person to just list all that for you, given all the sizes and types of magnets along with prop size that one can configure.

One other approach which has been used and posted by several of the more diligent experimenters on this board is to compare the output of your machine against the maximum Betz theoretical limit for a given rotor (prop) swept area. If your machine obtains 50% of the Betz limit it is doing reasonably well. (Im open to correction on this statement if anyone has different points of view).

Johnlm

Re: what performance in watts (3.00 / 0) (#2)
by Daggs on Thu Sep 8th, 2005 at 09:48:24 AM MST
(User Info)

What you could do is make a 3-d graph. Put rotor diameter on one axis, the RPMs on another, and the watts produced on the z-axis. That way you're comparing apples to apples, for the most part.

Re: what performance in watts (3.00 / 0) (#3)
by kitno455 on Thu Sep 8th, 2005 at 10:03:35 AM MST
(User Info)

no, there are other variables. number of turns, size of wire, number of phases, single layer vs multi-layer winding, single rotor or dual, iron behind, slotted iron, iron inside coils, iron powder, air gap size (stator thickness), star v/s delta, mag shape, mag surface area, mag thickness, steel mag plate thickness, magnet grade, etc.

fun!

allan

[ Parent ]

Re: what performance in watts (3.00 / 0) (#4)
by jimovonz (username at matata dot co dot nz) on Thu Sep 8th, 2005 at 02:30:44 PM MST
(User Info)

These are all factors that contribute to turbine efficiency, but it should be rather straight forward to compare actual efficiency for the same sized rotor. From comments on the board, many folk here compare the mesured output from their turbine to the Betz limit to get an indication of how well they have done. I agree with xymox, it would nice to see some tabulated data showing how efficient all these 'homebrew' turbines are at various wind speeds - however setting yourself up to accurately measure your turbine's power across a range of windspeeds would for a lot of people, be a project of similar magnitude to the making of the turbine in the first place...

[ Parent ]

Re: what performance in watts (3.00 / 0) (#8)
by Daggs on Fri Sep 9th, 2005 at 08:56:53 AM MST
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Those are all variables that are subject to the whims of the builder. There is a finite limit of power a generator can make, and that is based on swept area and windspeed. The variables that you mentioned are engineering solutions to maximize the efficiency, but the only way to compare one windmill to another is by watts generated per swept area. Even RPMs are irrelavant in an apples to apples comparison; RPMs can be tailored to acieve different cut-in speeds, but don't really change the overall effieciency of the windmill.

[ Parent ]

Re: what performance in watts (3.00 / 0) (#9)
by xymox on Mon Sep 12th, 2005 at 12:42:48 PM MST
(User Info)

I like that idea. I was thinking of a controlled experiment to some extent, I realize that many factors such as number os coils/windings wire gauge magnet grade. etc etc. all make a difference, but thats what I would like to weed out.
What is the "most" efficient design we can come up with. Yes I agree after reading through the replies, efficiency can be calculated a number of ways (dollar efficiency, power) but I am just concentrating on the power efficiency.
Maybe 100 rpms is to low as Hugh suggested. And I wasn't even thinking of blade diameters at this point. input power to the rpm of the test needs to be consistant (ie no loads or maybe a 100 watt light bulb) as does the rotor diameter, I like 12". Also a defined number of magnets(24 total) I am trying to encourage anyones idea on how to accurately measure performance in terms of power as it seems through reading the posts there is allot of variation in output.
Beat the system, do as much as you can do.
[ Parent ]

Re: what performance in watts do you see at 100 rp (3.00 / 0) (#5)
by scoraigwind (magnet@scoraigwind.co.uk) on Thu Sep 8th, 2005 at 03:55:25 PM MST
(User Info) http://www.scoraigwind.co.uk

When you say rotor it is not clear if you mean magnet rotor (on the alternator) or blade rotor (propeller)

For a given magnet rotor on a daul rotor machine I would be able to estimate the maximum power output at 100 rpm. However the alternator would only be 50% efficient at this maximum point and the 100 rpm speed is very low too. So not very useful although we could work on a better standard.

If you are asking about a certain blade rotor then the rpm is not a goo dthing to fix. Better to fix the windspeed and allow the rpm to suit the blade design. Again this can be estiamted - blade performance (of a certain diameter) at a certain windspeed.
Hugh Piggott http://www.scoraigwind.co.uk

Re: what performance in watts do you see at 100 rp (3.00 / 0) (#6)
by rotornuts on Thu Sep 8th, 2005 at 07:40:24 PM MST
(User Info)

Good point, wind speed given, swept area given and output given for the two preceeding variables. I'd hate to see wind speed fixed as well though as some machines seem to be built to optimise at different wind speeds.

Would be interesting, but in the end I like how Ed does it. A percentage of theoretical max. according to our pal Betz.

Mike

[ Parent ]

How about a competition? (3.00 / 0) (#7)
by cr8zy1van (salsa117@hotmail.com) on Thu Sep 8th, 2005 at 09:51:43 PM MST
(User Info)

Competition has always feuled advances in science and sports... lets have a little of both. Why not see who can make the most efficient design based on money spent... Since that is what we are all after in the first place. There would however need to be rules. Maybe you have to account for each piece of material used.. So no freebies, "Just happened to have a roll of wire and magnets in my shack out back" type thing. NOT to say that you cant scavenge, cause I don't see any problem with that... Anyone else's thoughts on this?

How about some numbers then..? (3.00 / 0) (#10)
by steak2k1 (theo12 at telus dot net) on Mon Sep 12th, 2005 at 06:54:58 PM MST
(User Info)

OK guys...here we go:

X 3/8 Rnd Neo 35 gauss, 12 ea 7" rotor
coils 40 winds ea
phase - star
/8+ a very small bit air gap
" wide laminate steel coil - glued and resin coated on back side of stator

no plywood used

who's gonna give me some #'S ...??? LOL..!

rgds,

stk
Awwwwwwk....It's Kenner - it's FUN.!!

what performance in watts do you see at 100 rpm? | 10 comments (10 topical, 0 editorial)

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