Is there an easy way to find out how much power my windmill is making?

[esc]

I have a very small windmill with a small PMA.  The only thing I can measure right now is open circuit DC voltage.
Is there anyway to estimate amperage (or ideally get to wattage) created at a given open circuit DC voltage?
I vaguely recall reading a formula based on the resistance of the coils...but don't know if that would apply to this situation.

If there is a way to do it you will probably need to know a little about about the PMA:

Dual rotor axial
8 poles
3 phase/3 coils/Star
Each coil consists of 500 turns of 26 AWG, 8 Ohms resistance
Rectified on tower(1.5 full wave bridge rectifiers from RS)
Measured 50 Feet away through some speaker wire (I expect this will cause some margin for error).  It seems to cause about a 2V drop vs measured at the tower.
Two 24" ZubWoofers (4 12" blades)

My problems are further complicated by the unbelievably poor location of my windmill.  Although I can move the blades by blowing on them, it spends most of the day sitting still.

It will make 5~6 volts @ about 50 RPM.
I have seen it reach 29 volts (open circuit) during an (estimate) 15 MPH gust.

How should I go about trying to figure out how many amps/watts it is making?
I don't need an exact figure, just a ballpark guesstimate.




Thanks

[ghurd]

Roughly, very roughly, just a poor ball park...

(Vopen - Vbat) / resistance = Amps into the battery.

Your first problem is resistance.  Big problem.
Each coil is 8 ohms?  X 3 coils = 24 ohms per phase.
Star resistance is then 48 ohms.

(29Vopen - 12.6Vbat) / 48 ohms = 0.34A

Next problem is in the PMA.  Something is not good.
500 turns per coil should be making a lot of voltage.  Especially with a 24" dia blade set.  Either the air gap is Way too much or ?

Confusing-
8 poles, 3 phase/3 coils/Star?
One coil per phase?  3 coils per phase, with 8 poles?
That could be the root of the problems.

I have a feeling it would do a LOT better with the phases rectified individually.

The length will not cause a drop if no current is flowing.  It was probably due to a slight change in the wind.
G-

[jlt]

Take a 12 v light bulb of a known amperage and see if you can keep it lit direct,from the mill. or get an amp Gage .harbor freight have testers. for volts &amps .

[esc]

ghurd,

Wait a minute, maybe I was not clear.

There are 3 coils total, one coil per phase.
So 8 ohms per phase, Star=16 ohms.

(29Vopen - 12.6Vbat) / 16 ohms =1.025A
1.025*12.6= about 13 watts?

The PMA is using 3/4" by 1/4" N42 magnets with about 0.45" air gap with 5" diameter rotors.
Like I said, it is in an incredibly poor location.  It will make about 6 volts spinning the blades by hand.
But the blades seem to spin VERY slowly even when a little wind does make it into the vicinity.

Considering 1 coil per phase do you still think that the voltage is too low?  I suppose, without any real RPM measurements, there is no way to know.  I'll have to see what I can do about getting some more data.


jlt
Maybe I need to get a clamp on multi meter from HF.  Think that would be useful?

Keeping the thing spinning long enough to do much testing is proving to be a problem.  I may have to relocate it to the top of my truck.    Or at least a near by field.  Right now it is on a 10' tower surrounded by 6' fences, 15' houses and 40' trees. 

[ghurd]

It may have spacing issues.  Either the magnets or the coils.
500 turns is an awful lot to only make 5~6V at 50 RPM.

Most probably have stalling issues.  That's what it sounds like to me.  Reaching cut in at 110~125RPM is crazy slow for 24" dia blades, even with PVC blades.  If the blades are made from 4" dia PVC, then it is certainly stalling.

HF clamp meters only read AC amps.
Just get the regular HF one on sale for $3.

I take my stuff to a causeway for decent testing.  Only place around here to get smooth steady non-gusty reasonable speed wind.
So I know how you feel.
http://i701.photobucket.com/albums/ww20/ghurd1/PICT0333.jpg

G-

[esc]

If I do have magnet/coil spacing issues...what would the ideal spacing look like?
Yes, they are 4" diameter PVC.
Stalling issues?
How could it stall with no load?  

[ghurd]

Ideal spacing would look like a 6/8 dual rotor.
Except in your case, with half the coils removed?

If there is no load, and it is still going slow, then there is a problem with the blades.
5~6V at 50RPM, and only 29V open in 15MPH wind, is maybe 264RPM (assuming the coils and magnets are spaced semi-correctly).

264RPM with 24" dia PVC blades made from 4" PVC in 15MPH wind sounds like a fairly serious blade problem.  They should be scooting along pretty nearly 1000RPM unloaded.

If you have not changed the stator from earlier, then I doubt it is good enough to get meaningful readings.
Got any pics of the stator and magnet disks?

[tanner0441]

Hi

I have made several sets of PVC blades, using an Ametec 24V type motor as a bearing and even in my poor wind area the blades would spin up enough to make a satisfying swishing noise. In your situation I would put an anemometer on a pole and see what your real wind situation is like. Plus the fences and house proximity probably means the real wind versus turbulence is a very uneven battle.

Brian.

[esc]

I have started a new thread with specifics about the coil and magnet alignment here:

http://fieldlines.com/board/index.php/topic,143425.0.html

[Ungrounded Lightning Rod]

You really need to measure it under load.

In addition to, and far more significant than, the resistive voltage drop, is the effect of load torque on the the RPM of the mill.  This is an issue with the aerodynamics of the blades.

If you assume the RPM under load will be half that when the circuit is open, you can figure your voltage BEFORE resistive drop will be half the open circuit voltage.  I hear (on the board) that half-unloaded-speed-at-optimum-TSR is typical for good airfoil design blades - but don't know this for a fact.  For other blade types I'd assume it's even more iffy.

[bob golding]

if you got a doc wattson meter and put it between the dc side of the rectifier and the load that will give you the total current voltage watts and max current and voltage. cant remember the maximun voltage but the maximun current is 60 amps. very usefull device as long as you dont  get it wet or overvolt it. about 60 dollars.

[sanches]

I want to have a meter for measure to power. The turbine power is about 5 kW, it is connect to controller and go to the accumulator about 1000 Ah. Could you tell me how do can I do it?