How to measure 3 phase from windmill

[mat]

I have just pup up my windmill and am a little disappointed in the output. I have a 24 volt piggot windmill. I can measure the output on the ac side of the rectifier between any two wires of the three and get about 20 volts in moderate winds. How do you measure the amps so i can get my wattage out put? The windmill is connected directly to the battery which runs about 24.8 volts. I disconnected the battery and tested the DC current and it got up to 30 volts before I quit. Everything seems fine but I wonder if i am doing any charging? My solar cells produce about 500 watts on a good day and they make quite a difference to the fork lift battery.... but the windmill seems to have little effect. Any suggestions?

-mat

[Flux]

You measure output current with an ammeter in the dc line between rectifier and battery. DC current x battery volts gives you power out.

You would expect somewhere in the region of 18v ac on the input of the rectifier so your 20v figure seems normal.

If you got 30v on open circuit you will be charging, but it is an indication that you have little wind or you have done something wrong with the blades ( usually it is the wind at fault).

In a good wind area with the output open circuit you would see the blades race away and the open circuit volts on a 24v machine could easily hit over 100.

You don't say how big your mill is, but in a low wind area you may be looking at only a few tens of watts. You will need decent wind to see anything comparable to your 500W of solar. If your blades are right I wouldn't expect you have much over 12mph wind speed so you are not going to see spectacular output, but it does seem to be working. I can't imagine anyone having a wind turbine with no ammeter but it seems a common trend here in the last few days.

Flux

[mat]

Thanks. From what I see it could be low wind yesterday.Today the heat sink is actually warm and the wind has picked up. I am on the north edge of lake erie and there is a lot of wind here. Yesterday the winds where light today they are better. My blades are about eleven feet in dia. OK where do i get an ammeter, what type should I get that I can tie in?

Thanks for your input -mat

[TomW]

Flux;

I can't imagine anyone having a wind turbine with no ammeter but it seems a  trend here in the last few days.



These folks should find a bit over a foot long hunk of #10 copper wire feed the mill power thru that. Then they could measure millivolts directly as 1 mv = 1 amp current flow across one foot of that to get a ball park idea of the performance. Even the cheapest meters read dc millivolts[mv.].

I know you are aware of this, but just tossing it out there as a poor mans way to get amp readings for those who may not know it.

Thanks for all the effort you put into helping folks out here, Flux. Really.

TomW

[Boss]

My favorite method is with a oscilloscope. Lacking this tool, an AC ammeter on each leg should work. The better and more accurate method is as they say above a clamp-around  ammeter  

I like Fluke but they are spendy

http://metersuperstore.com/

[electrondady1]

an automotive parts store or electronics supply should be able to fix you up.

[Capt Slog]

I use one of these...

http://www.otherpower.com/otherpower_experiments_ammeter.html

Easy to make and great fun to watch.

The only worry I have with it is how much could it take before it becomes a fuse?

[Flux]

Everyone has their preferences. A shunt is the easiest way and Tom's foot of #10 wire is good enough for this degree of accuracy. It is fine for digital voltmeters but I like analogue displays for wind ( digital is ok for battery volts). It is possible to use the simple wire shunt with analogue movements but it requires extra knowledge unless you know your meter reads millivolts. You also need to understand lead length.

There are moving coil meters about with internal shunts up to about 30A sometimes larger. More expensive are industrial shunts, usually 75mV and associated ammeters.

Automotive ammeters are good enough, even the moving magnet things where you thread the cable through a loop at the back are good enough.

A scope has its uses in research but I don't consider it a good choice here, neither do I consider an ac clip on ammeter to be a good choice, maybe that having spent too long in a measurements laboratory has made me realise many traps and pitfalls that others have fallen for.

If you want to measure power into batteries you need dc mean and the best place is to measure that on the dc side. AC measurements will show if you are charging or not but that is about as far as it goes.

Flux

[mat]

I really want to refine the whole thing. Is there any use to putting a controller in the system such as my solar cells have? I notice that my outback controller takes whatever it seems to get and output it in 24 + voltage. I do have the one C60 controller for the diversion load which heats water. If I feed the dc from the rectifier to a controller then go to the battery is there any advantage?

thanks -mat

[Flux]

As far as I know there is no commercially available mppt controller for wind and battery charging. No there is no controller that you can put between the turbine and the battery. You need to be content with a diversion controller connected directly to the battery.

"If I feed the dc from the rectifier to a controller then go to the battery is there any advantage?"

Yes indeed there is and it can be a dramatic advantage, just keep your fingers crossed and hope the Classic comes out soon. With such a controller, 1kW from a 6ft machine with less than 30mph wind speed is a perfect reality.

Flux

[DanB]

This (in my experience so far...) is a nice inexpensive meter:

http://www.rc-electronics-usa.com/ammeters/r102-amp-hour-specs.html

[Basil]

I used a 0 to 15 amp meter out of a dead battery charger.

[David HK]

Flux,

Since you mention it here, could you please expand on what you know about this 'Classic" charge controller. It sounds very interesting and knowledge would be useful to all.

David HK

[Volvo farmer]

I was talking with my solar supplier today and he said he saw boB walking around recently with an actual Classic in his mitts. All speculation but perhaps shipping by this summer? Also heard the Classic is good to 250V on solar. I seem to remember more stuff needing to be figured out on the wind part of it, such as a custom made dump load or something.

I wonder what kind of performance gains could be had winding these stators for 200+ volts? It would certainly save on copper down the tower if nothing else.

[Volvo farmer]

http://www.midnitesolar.com/classic%20development%20update3.pdf

[electronbaby]

You should be able to use the MX80 for wind (continuously tracking MPP) as long as you have a voltage clamping device or crowbar across the input (windygirl?? they make a 60v version) You would prob void the warranty, but it should work fine as long as you sized the turbine output accordingly. I would love to get my hands on a Classic controller for beta testing. That would be fun. :-)

[cardamon]

electron,

Do you mean the flexmax 80? Is the mppt algorithim for this much quicker then the mx60's?  I know they say continuous but I wonder what exactly that boils down to.  I heard that the mx 60 takes several minutes to refresh its MPP, obviously way to slow for wind.  If the 80 has a much better refresh rate, the regulation point is set higher then your diversion controllers, then i could see that working

[electronbaby]

the whole idea basically is to allow the turbine to run up to the maximum voltage and clamp the current at a point along the rpm curve that the prop will run most efficiently. Most MPPT controllers will do this. It might not follow the curve exactly, but the most important part is to do the buck conversion down to your battery voltage and take that heat out of the stator, allowing it to run more efficiently. This allows the alternator to produce power more efficiently over a wider range of RPMs. The faster refresh rate is nice, but is not critical. The most critical part is that the controller does not go open circuit while its sweeping, allowing the turbine to freewheel. I dont have experience with the flexmax 80 but i might get one soon. Im in the process of converting all my stuff over to outback equipment.

[Flux]

David

Sorry I know virtually nothing about the Classic except that boB is working on it. I did supply him with some chart recordings giving an indication of how the output changes with wind speed, but other than that I know very little. There may be others working on this but I only know of the Classic.

My knowledge of the performance is based on my own tests with an analogue scheme and that is not a true tracker. It just matches the alternator power curve to the prop. It would need to be set up for each individual condition but it so happens that when you include alternator losses and the peculiarities of my type blades, tracking the output power to the square of alternator speed gives a very close result and the set up for different alternators would be just to match the cut in point.

I can't help feeling that Jacobs and Dunlite got very close to this years ago with their dc generators but didn't have the option of raising the generated voltage with wind speed to reduce losses.

Flux

[David HK]

Dear Flux and everyone else,

As always, one post is out of date the moment it is sent. I'm grateful for the time you have taken to write a reply, and I am also grateful for the 'links' which tell a bit more about this 'Classic' thing. It looks as if it has potential so I am sure we await developments with interest.

David HK

[cardamon]

If I am understanding this right, then It seems that there are two different approaches to wind mppt. One is to have a pre programmed mppt curve that the controller looks up values from.  Another would be trial and error, where the controller sweeps around to try to get a bettter gain.  I think solar mppt use both in practice;  they start at a theoretical value and then hunt a bit to try to do better.  I would think that with wind a fast refresh rate would be critical, otherwise the controller could be way off for some period of time?

[Flux]

That's my take on it as well.

I see wind being so variable that direct tracking is very difficult especially as you have inertia to contend with.

I think the Windy Boy grid tie lets you change a few points on a general curve to suit different machines.

I an not a digital man so take this with a pinch of salt. I see the logical approach as a look up table with a long term learning facility. Any machine would then slowly learn the correct curve and if you changed battery volts or something it would re-learn it.

This would mean that the user would not need to programme it. I can only imagine that this is what engine management systems on cars do. They don't stop if you loose a sensor, they just revert to a default with perhaps a drop in performance.

If I could do digital things then that would be my approach, As I can't I use analogue methods to do the equivalent of a programmed look up table. I would never attempt to chase the wind all the time.

Flux