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Wind alternator not pumping subtantial amount of electrons.
By s4w2099, Section Wind Posted on Fri Jan 19, 2007 at 04:24:13 PM MST
Hello guys here I give you a link so you can see my situation with my first alternator. its 2.1M

Hello guys here I give you a link so you can see my situation with my first alternator. its 2.1M http://rabilco.com/ahome/win.mpg The problem is that at the RPM shown in the video I only get like 9.5 volts (after rectification with a capacitor filter 2200uf@100v, no load, star configuration). The current is about 3-4 amps per phase and this is a 3 phase alternator with 3 coils per phase 50 turns per coil. My magnets are N50 2x1x0.5 in a double rotor config. The rotors are 11" diamater and its a 12 pole machine. I dont know if I am being paranoid but it looks that the voltage its too low for that RPM to charge a 12v Bank. I will use a 2 meter diameter propeller so I doubt that it will spin much faster than that. I dont have much tools to test this (you see in the video that I am spining it with a kitchen spoon. :-(

Wind alternator not pumping subtantial amount of electrons. | 18 comments (18 topical)

Re: Wind alternator not pumping subtantial amount (3.00 / 0) (#1)
by tecker on Fri Jan 19, 2007 at 09:42:46 AM MST

Run it up 100 rpm and check it again

Re: Wind alternator not pumping subtantial amount (3.00 / 0) (#2)
by Flux on Fri Jan 19, 2007 at 10:06:39 AM MST

Sorry the link is useless to me.

Let's have some more details. 12 poles 2 x 1 x 1/2 with 50 turns should be very slow for a 2M prop. Unless you have done something incredibly stupid you should get 12v below 150 rpm.

You give no idea of your test speed but you say you are turning it with a spoon or something.

Get someone to shout out seconds and turn it at 2 revs/ sec, 120 rpm and come back with your voltage figure.The capacitor doesn't really do anything if you have a 3 phase full wave bridge rectifier but it doesn't do any harm.

Not sure what you are intending to use for a prop but cut in at 250 rpm will be ok and I suspect you will be way below that. Probably too slow unless your coils are about 1" thick.

If you have a meter to measure volts you have all the technology you need to measure cut in speed.

If you give more details of the alternator with coil thickness Gap between magnets and wire size I can check your figures. I suspect you are turning it at under 100 rpm and you wildly underestimate the speed of a 2M prop. Let me know if the prop is anything other than a normal carved wooden one with tsr 6 or 7. If you have a fan off a wind pump or something it skews my thoughts.

Flux

[ Parent ]

Re: Wind alternator not pumping subtantial amount (3.00 / 0) (#3)
by s4w2099 on Fri Jan 19, 2007 at 11:31:11 AM MST

ok, the air gap is about 1/4 inch each rotor. And my coils are 1/4 inch thick. I really cant imagine something as big as 2 meters (the prop) will spin as fast as 200 RPM+ under normal wing conditions 10mph average. Can a 2 M prop spin that fast? I have not built one yet but I think I will use PVC pipes ince I dont have many tools. I ran some other tests. I used a brooms stick and a drill to spin the alternator at constant speed and I was able to see a buffered voltage of 20v across the capacitor this time. Then I shorted the output and only saw 4-5 amps in the meter. The drill is suposed to be a 1500 RPM machine and I was only going half of that speed or maybe a bit less, and since It was under load I guess that it was doing 200 RPM MAX. I connected a battery that was sitting still for a while with a voltage of 12.20 (very discharged) and it only took about 2amps. So 2 amps @12v = 24watts. :-( I was suspecting on the stator winding polarity but after running voltages to them all are connected start to end in each phase. (Tested with a magnet for polarity). I know that if I spin it faster it will produce great currents into the battery but I wanted a slow alternator since I was figuring that a 2 meter diameter prop would not spin that fast. But aparently I am wrong about the speed of the prop.. Please advice me. Thankx

[ Parent ]

Re: Wind alternator not pumping subtantial amount (3.00 / 0) (#4)
by TomW on Fri Jan 19, 2007 at 11:55:06 AM MST

s4;

Well, I have a 2 meter prop on a conversion that must get up around 500 rpm and is not scary since it is well balanced.

Just my experience. No tach on it but it gets to be a blur right quick.

Cheers.

TomW

The Truth is the Truth, even if no one believes it; and a lie is a lie even if everyone believes it

[ Parent ]

Re: Wind alternator not pumping subtantial amount (3.00 / 0) (#5)
by Flux on Fri Jan 19, 2007 at 11:57:52 AM MST

Thanks
With coils only 1/4" thick you will have had to use fairly fine wire so you may have more resistance than normal.

Don't follow the air gap thing. With 1/4" thick coils in a 1/4" air gap they would just touch the magnets. Do you mean you have a 1/4" clearance each side making 3/4" total air gap?.

Your speed is obviously plenty low enough. I know absolutely nothing about pvc pipe blades but even they should be fast enough.

200rpm at 10 mph should be perfectly easy to obtain with reasonable blades.

At 2.1M you are not going to see more than 3A or so at 10 mph so everything seems reasonable.

Flux

[ Parent ]

Re: Wind alternator not pumping subtantial amount (3.00 / 0) (#6)
by vawtman on Fri Jan 19, 2007 at 12:04:23 PM MST

Any chance for clear and closeup pic?

[ Parent ]

Re: Wind alternator not pumping subtantial amount (3.00 / 0) (#7)
by s4w2099 on Fri Jan 19, 2007 at 12:06:40 PM MST

Sorry, I have used 15 AWG wire, each phase is about 0.7 ohms. Yes, the CLEARENCE between the rotor and the stators is 1/4 inch. So do you guys think that the problem is low speed? Because the resistance is not that much. 12=I*0.7 so the amperage should be 17.14A. Thats why I am asking these questions. My numbers do not seem to be acurate compared to the result. thanks

[ Parent ]

Re: Wind alternator not pumping subtantial amount (3.00 / 0) (#8)
by s4w2099 on Fri Jan 19, 2007 at 12:08:48 PM MST

oops clearence between rotors and stator..

[ Parent ]

Re: Wind alternator not pumping subtantial amount (3.00 / 0) (#9)
by Flux on Fri Jan 19, 2007 at 12:24:58 PM MST

That air gap is rather large. You really have nearer a 24v winding.

I think you are totally missing the point that there is only about 40W available from the wind at 10 mph. It is totally useless messing about with the alternator to make it produce 17A at such a low speed. I am sure it will stall now and if you reduce the total air gap to about 1/2" the cut in will go below 100 rpm and it will just sit stalled making just a few amps in any wind.

You can't hope to get the 17A at wind speeds below about 16 mph and you need the alternator running at nearer 400 rpm.

Your method of estimating current is wrong but that doesn't affect the general argument.

For a given size of prop there is a maximum power out that you can expect at any wind speed and unless you run the alternator at the best speed you will never get even close to those theoretical limits.
Flux

[ Parent ]

Re: Wind alternator not pumping subtantial amount (3.00 / 0) (#10)
by s4w2099 on Fri Jan 19, 2007 at 01:31:41 PM MST

ok, more info. At about 180 RPM (a wild guess, dont have a tach) I am getting 2.3 amps and the battery voltage goes from 12.26 to 12.68 wich for a 12v battery is a lot. Remember I am using a 6 amp drill to turn my alternator. 29.16 watts I get by doing P=2.3*12.68 (again, dont know how correct could this be). Does those figures sound right?
I dont know if these readings refflect the amount of charge that the battery can absorb since I am using a 60 amp/ hour battery, deep cycle.
So, I shorted two of the three output therminals and measured the current and it showed 7amps and the rotation speed I would say was about 100 RPM since the drill would not have enouth torque to speed it any faster. What do you think about this one?
thanks

[ Parent ]

Re: Wind alternator not pumping subtantial amount (3.00 / 0) (#11)
by Flux on Fri Jan 19, 2007 at 01:54:45 PM MST

Your wattage figures of battery volts x current are right. 30W at 180 rpm is reasonable for your 2.1M prop. Your battery is fairly well charged if 2.3A brings the volts up that quickly. This doesn't affect the argument much, it just alters the cut in speed slightly.

The short circuit readings are virtually meaningless, you may have 7A but there is no power produced. I am not sure how you are measuring this short circuit current, it sounds as though it is a single phase short and I can't think where your meter is connected. Anyway as I said the short circuit readings tell you nothing.

I somehow get the impression that you are still expecting much more output at this speed and there is not much more I can do to convince you that it is not what you need and even if your alternator could produce it, you would never see even 30W at 10 mph with a 2.1M prop hard stalled.

Flux

[ Parent ]

Re: Wind alternator not pumping subtantial amount (3.00 / 0) (#12)
by s4w2099 on Fri Jan 19, 2007 at 01:59:25 PM MST

ok, sweet, I was just trying to figure out if my alternator output was reasonable compared to what you guys have built with experience. Remember, This is my first alternator so I dont have exp. about the power output that it should produce.

Thanks a lot for your help guys, It was very helpful.

[ Parent ]

Re: Wind alternator not pumping subtantial amount (3.00 / 0) (#13)
by Flux on Fri Jan 19, 2007 at 02:53:47 PM MST

Yes it is reasonable. Not sure about pvc blades they may run slower, but with the usual wooden ones I think your cut in speed is on the low side. Try it as it is, but you may need to increase that air gap even more.

If you ever decide to upgrade to 24v just close up that air gap and the same winding will do.

That amount of magnet especially with N50 would handle a 2.7M prop with 24v.

Ultimately what you get out of it will depend on the wind you have. If you are in a desperately low wind area then 2.1M is rather small, but if you have good wind you should see up to about 400W quite often if you can keep it out of stall.

Good luck, keep us posted with how it turns out.
Flux

[ Parent ]

Re: Wind alternator not pumping subtantial amount (3.00 / 0) (#14)
by s4w2099 on Fri Jan 19, 2007 at 03:31:53 PM MST

I was about to ask you the same. Thanks I will make my alternator tighter to see if I can fit a bigger propeler. Thank you :-)

[ Parent ]

Re: Wind alternator not pumping subtantial amount (3.00 / 0) (#15)
by Flux on Fri Jan 19, 2007 at 03:52:19 PM MST

I am not sure what the limits are for pvc. Perhaps others can help you, but I would be afraid of big ones bending back and striking the tower.

Flux

[ Parent ]

Re: Wind alternator not pumping subtantial amount (3.00 / 0) (#16)
by luckeydog on Fri Jan 19, 2007 at 11:43:44 PM MST

If you are planning to make your turbine blades out of PVC at 2m then you will need to reinforce the blades with fiber glass or even better yet carbon fiber. if you are in a cold climate i do not recommend PVC it becomes very brittle at cold temps . if you would like to test this cut a 1 foot piece and place it in the freezer for 1/2 hr. and then go toss it on the ground and it will shatter. PVC is OK for small turbines but for a 2m. I would not walk under it. My suggestion is carve a set of blades I think you will get the results you are looking for.

Luckeydog
wind gens are much funner to watch than solar panels. Broomfield,Colorado
[ Parent ]

Re: Wind alternator not pumping subtantial amount (3.00 / 0) (#18)
by s4w2099 on Sat Jan 20, 2007 at 05:58:50 PM MST

Thats good information to have. I was about to make a terrible mistake. Right now I am covered in snow. Thanks again

[ Parent ]

Re: Wind alternator not pumping subtantial amount (3.00 / 0) (#17)
by finnsawyer on Sat Jan 20, 2007 at 09:07:30 AM MST

I disagree with your statement that the short circuit current measurement is virtually meaningless. We know that the alternator puts out 2.3 amps at 12.26 volts and 7 amps at zero volts. If we assume linearity we can use a Thevenin equivalent model to calculate the open circuit voltage and equivalent resistance of the alternator. If we do so, we get a resistance of 2.6 ohms and an open circuit voltage of 18.2 volts, which is easily checked.

For the record the equations are: Voc = 2.3xR + 12.26; Voc = 7xR.

Of course, this is a model for the alternator as it appears electrically at the battery terminals. That is, for DC. Keep in mind that the numbers can also be affected if the speed changes with loading. The speed should be kept constant.
GeoM
[ Parent ]

Wind alternator not pumping subtantial amount of electrons. | 18 comments (18 topical)

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