A Classical case of stalling.

[seanchan00]

I have bad stalling. In moderate winds I see the blade speed increase and the amperage start to rise and the moment it reach 2 to 3 amps it immediately falls to less than half an amp. I removed the three cables to the rectifiers and then saw the blades really fly fast. When it has reached speed enough to be heard I reconnected and immediately the blades slowed down. I definitely have to open up the air gap between the rotors. Right now each rotor is just about 1/8 inch from the stator. Do I double up or just adjust by trial and error empirically till it no longer stalls? Going to be very tedious lowering and raising the tower repeatedly. Any suggestions?

My wind generator is a 8 feet 6 inch triple blades mounted over 12 inch 12 pole dual rotor alternator with 24 neodymium magnets (2"x1"x1/2") and a stator of 9 coils 35 turns of double strand SWG 16 ½ diameter 1.5 mm magnetic wire. The thickness of the stator is just over half an inch.

Please help. It is not easy to lower and raise the wind tower repeatedly.

SeanChan.

[willib]

is that 8' 6" dia. ?

i'm no expert on blades , but if it is stalling that badly ,i would put some larger blades on the baby..

[seanchan00]

I aim to do so (12 feet diameter blades) but in the meantime my power needs can only be hoped for by opening the air gap.

SeanChan.

[willib]

It sounds like a beautiful machine with very ,very low internal resistance .

what kind of voltage is it putting out at the stated current ?

kinda seems like a shame to open the air gap  , just because the blades are too small..

[seanchan00]

Yes you are right. I have no idea of voltage and current figures but spinning by hand I could easily light up a 20 watt flourescent light. Like I wrote the moment the ammeter rises above 2 to 3 amps it drops immediately to negligible reading. The voltage rapidly rises to battery voltage when it starts to turn. Until I can make the new blades I need to open up to get less than optimal power but some is better than almost none at present.

SeanChan.

[harrie]

Hi SeanChan.   It sounds like your running in Star, try Delta, that may help. Yes, you do need 12 foot Dia. prop. Otherwise I guess you could open it up to get by for now, or go with 2 phase instead of 3, but you will get alot of viberation. Im still learning too, so good luck. Harrie

[RP]

I think it'd be a good idea to get some voltage measurements.  If your no load voltage is high enough, you might be better off wiring the 3 coils in each phase in parallel instead of series.

Also, if this is just a temporary condition until you get your 12 footers up, how about just adding some resistance in the line.  You'll waste some power but it sounds like you can't capture what's available now and it'll save having to take it down again.

[willib]

a less drastic approach would be to add a resistor in the line between the rectifiers and the battery..

At 3 A the voltage drop across a 1 ohm resistor  is 3V.

3V * 3A = 9 Watts so try a 1 ohm Ten Watt resistor , Radio shack has them..

[willib]

RP , i didnt see your post , but i agree a resistance is needed..

Did you know that some wind farms  in japan and canada are using giant  Flow Batteries to take up the slack between production and demand?

been looking at your photo uploads..

[seanchan00]

I certainly expect more than 3 Amps from the generator if it does not stall. Will the 1 ohm 10 watt resistor still suffice?

SeanChan.

[willib]

it appears that your present props can only sustain a current of about 2A before stalling , i am not sure if a one ohm ten watt will cure your problem but two in parallel can handle twenty watts , all i can say is try it .

[RP]

Just for testing:  Try 1 or 2 old headlights from a car or 20-50 feet of cheap (thin) extension cord as a temporary resistor.  This might at least tell you if you're on the right track.

[Flux]

You shouldn't be stalled that badly, I would have expected stall to limit you to about 10A not 3.

I don't like the fact that you say that it goes up to 3A and falls back to 1/2A.

Can you find another battery and try it at 24v as a temporary measure.

Also if you can easily get at the rectifier try it single phase by removing one ac lead at a time. It may be worth trying each one at a time, I have some reason to suspect you have a rectifier fault and the effect of each phase removed should be the same. If there is a rectifier fault then the effect will be different as you remove a phase..

If this is only stall , it will run perfectly well into 24V at winds above 10 mph and you should see at least 12A at 20 mph.

With it on 12v and single phased you should not stall but the efficiency will be lower. If the thing works much better with one phase removed than the other 2 then suspect a shorted diode in the rectifier.

Your alternator should cut in at 12v at about 160 rpm, a bit on the low side for an 8' 6" prop but not seriously so for a 12v system.

I think you said you disconnected the ac leads from the rectifier and it speeded up, try leaving the ac leads connected and disconnect the dc and see if it runs as fast and if you have a clip on ammeter, check for current in the ac leads. If there is current it again points to the rectifier.

Others have suggested a resistor in the dc line, you can also try this and it will help if it is stall. You will need something less than 1/2 ohm and you are probably more likely to find a long piece of cable or a short piece of steel fence wire than a dedicated resistor for a quick test. Cheapie ww resistors from mickey mouse radio supplies will fry.

If you can eliminate the rectifier as a source of trouble and prove that it works well into 24V then open the magnet rotor gaps to 3/8" for a first try.

If the rectifier is ok and it doesn't perform into 24v then you have the other thing that I suspect, turbulent and useless wind, I hope not there is no cure for that without very tall towers.

Good luck.

Flux

[seanchan00]

Thanks for such detailed help Flux. I need to clarify a few of your pointers as I do not wish to get it wrong.

I have 2 separate sets of 3 rectifiers at ground level fed by the same 3 AC leads going to two 12 V batteries. Both are showing same sickness.The rectfiers are rated 35 amp bridge rectifiers. Before I put the windgen up I tested each star AC lead by hand spin and they all showed same voltage of 15V AC plus or minus depending how fast I spun.

[try leaving the ac leads connected and disconnect the dc and see if it runs as fast and if you have a clip on ammeter, check for current in the ac leads. If there is current it again points to the rectifier.]

a) Will removing the connection to the batteries be what you instructed above?

b) How do I measure current in the AC lead? I have only 3 AC star leads down at ground level. The other 3 leads are wired in series up at the alternator.

[If you can eliminate the rectifier as a source of trouble and prove that it works well into 24V then open the magnet rotor gaps to 3/8" for a first try.]

c) 3/8" each side of the stator? Or 3/16" each side of stator.

d) I presume I have to test each set of rectifiers separately. Disconnect one set from the AC leads and test the remaining set? The same should apply if I try charging into 24V system or I just do 24V charging for both at the same time?

I have always been able to solve my problems with your help. This surely won't be different. Will report after checking tomorrow. Meantime I hope to receive your clarification before I test them.

Thank you again.

SeanChan.

[Flux]

To simplify things for now, disconnect one of your rectifiers.

At this stage you could try with one rectifier and one battery. If still the same try the other rectifier and one battery, it is highly unlikely that you will have 2 sick rectifiers.

If the problem remains then use one rectifier and feed your 2 batteries in series, that is the 24v case that I meant.

Removing the battery connection is the same as opening the dc side of the rectifier, but in view of the fact that you will most likely not have 2 dead rectifiers I doubt that you will need to do this test. If you don't have a clip on ammeter it becomes a bit of a nuisance to check the ac line currents.

If you don't find a faulty rectifier when you try each into 12v, I would go straight to trying one rectifier into 24v. This will remove any possibility of stall but you do need a reasonably windy day.

If it comes to life into 24v then you have proved stall. If it is stalling that badly you need a fair increase in gap so try 3/8" each side. going from 1/8 to 3/16 will not be enough.

Flux

[DanB]

My thought would be larger blades as well.  But to match the alternator to what you've got I expect opening the airgap would be appropriate.  For 8' 6" blades I'd shoot for cutin somewhere around 160 rpm give or take a bit.  Right now you're probably well below that.  I'd guess add something like 1/8" - 1/4" to the overall airgap (so half that on each side of the stator.

If you get the cutin speed right and it's still stalling, adding resistance to the line would probably get things right.

[seanchan00]

Hi Guys,

It is stalling. I disconnected one set of rectifiers and wired the other with 2 batteries for 24 V and there is very obvious increase in speed of the blades although the wind was very marginal. As you indicated Flux I do need strong winds for 24V charging since my stator is 35 turns for 12V charging. The voltage in the open rectifier reached 20V but not enough to show charging. The monsoon is still pouring after 3 days of non stop rain going into the 4th day with no sign of letting up so I can't bring down the tower to open the gap. I will try to add thinner wire to the line to one battery till it overcome stall and add the same length to the other battery. Maybe that will solve the problem till I get the 12 foot blades. The marginal wind conditions here will be compromised by reducing the flux with air gap opening. That will the the best way to solve it. All others are temporary as it reduce the power available in low winds mostly seen in my farm here.

Thanks for all your useful suggestions.

SeanChan.

[Flux]

I don't think it is stall, seems more like lack of wind.

As soon as any power is generated the blades will slow down, this is normal. If you can't reach cut in speed at 24v then you will not be stalled at 12v, just turning at a speed to produce the power available.

Don't increase the air gap, by all means try added resistance but I don't think it will help in your case.

Bigger blades will capture more power and that is your only chance of significant improvement.

I had a feeling the problem was wind but now you have proved it fairly conclusively.

When a machine stalls the current increases to a certain point and holds virtually constant, it does not drop off as you noticed. You are extracting the most from short gusts.

Flux

[seanchan00]

I will be able to watch it today for a longer period. On that day there was very little wind and a lot of rain. I could only watch for less than 15 minutes before the rain started again. It has been left for 2 days at 24 V charging but there has been even less wind because of the monsoon rain. Seems to have finally stop after 5 days of it and I hope for better wind conditions today before I do any changes. Will be mainly watching the performance. Thanks for your good opinion. Will have what you just wrote in mind when I observe later in the day.

SeanChan.

[rotornuts]

Is there any chance your machine is located in turbulent winds such as near an obstruction or below the treeline etc...

Mike

[seanchan00]

Other than being cursed by marginal and sporadic winds and evidence of stall, the wind from east and south is blocked by trees. I intend to bring down the trees east of the wind generator to improve the result. I have added 3 times the wire length and there is very clear inprovement. Now I can see as the blades speed up the current rises proportionately to almost 3 amps stays for a few seconds then most of the time falls to 1 amp. The wind is really sporadic and I suppose turbulent. The prevailing winds here is north-east for half the year then south west the other half but being inland and in rolling low hills it is not constantly working for my benefit.

I intend to increase the wire lenght step by step to see if I can get more inprovement. The blades seem to be more alive now and when the current rises it stays up at the level relative the wind speed. The comparison is coloured by the fact that the winds has picked up compared to before I increase the wire resistence. I have no way to measure wind speed and I can not estimate the power expected at certain winds so I can't tell whether It is still stalling a little.

SeanChan.

[Flux]

You could arrange to cut out the extra line resistance quickly so that you could compare it with and without. It may be the change in wind is having the greater effect.

Get those trees down, that may help, you obviously have a terrible wind site.

We have never discussed the prop, perhaps you could give some details in case something is very wrong but I doubt it in your case, you seem to know what you are doing.

Flux

[seanchan00]

My initial connection is a 60 ft pair of 2.5 mm square 7 strand wire. I increase it first to double the lenght, no diff. Then to 3 times the lenght which is about 180 ft and that's when it seems to function with much inprovement. 2 days ago I added another 60 ft same wire and it was evening 6 o'clock with really calm conditions. While I was watching the wind rose a little and it really spun like it is free and kept spinning very happily and seemingly much more smoothly in real low winds but no amps was seen as the wind was too low. At that speed of blade rotation I would have seen the ammeter start to rise with 3 Xs lenght. Now with 4 Xs lenght I presume the cut in speed would have gone up somewhat. I have left it as such and see after 3 days whether the battery received any significant charge. I don't stay on site and it is difficult for me to see what's going on at the wind gen. My next direction would be to do as you said, cut off excess lenght quickly and see how the result during good winds. That is easily done as the wires are connected by plastic block connectors. Have to be mindful I don't connect wrongly. I read 8 amps during wire adding and found I reversed the last connection so shorted the battery. Happy for a split sec till I saw the blades was not moving though.

Trees are coming down as fast as I can get the logger to come.

You can see my blades at this site with pictures. Its based on Hugh's splendid design as closely as I could.

http://www.fieldlines.com/story/2005/8/18/0340/28458

SeanChan.

[Flux]

Thanks . If you made those blades to Hugh's dimensions then they will be fine.

From all the other details on that post I suspect your cut in is about 150 rpm, which is low for that size of prop in a normal wind area but you may need it to be that low with your poor wind.

I find that you need about 0.35 ohm lead resistance to avoid stall and that works out to about 180 ft of your 2.5mm square wire so you should be close with what you have added.

Cut in speed is not affected by wire length so you may still see an improvement with the 4th length when the wind comes. If is difficult to guess speed.

Connect a short piece of wire in each connector where you have added the wire, then you can just short the ends together to take that length out of circuit with no need to disconnect anything.

I don't think your extra 4th length will do any harm and should keep you out of stall. I doubt with your wind you will see any serious loss from too much resistance.

Flux

[seanchan00]

Thanks for your reassurance, Flux. I am keeping my fingers crossed to see the expected inprovement tomorrow afternoon when I go in. In the next few weekend days I will definitely do as you advised. Short it to see the diff. I have got my hands on three 7 to 8 ft 7 inch by 2 inch lumber which I would make my 6 feet blades and I will start on them when I come back from my Lunar New Year holidays. From your experience, in low wind areas will you go for smaller diameter blades example 8 ft with smaller alternater such as hugh's 6 coil dual rotor 8 magnets OR bigger 12 ft diameter blades with coresponding bigger alternater like this 12 inch dual rotor 12 magnets with 9 coils ?

SeanChan.

[Flux]

For very low winds you need a big prop. I was assuming you were going to use the 12ft prop on the existing alternator.

You will gain nothing by using 8ft blades with another alternator over your present one when you get it properly matched.

The available power goes up as the square of the diameter so size means everything with low winds.

Flux

[seanchan00]

HI Flux,

Been away for two weeks in New Zealand for my Chinese New Year holidays and had a wonderful time. I came home to see all my batteries flat and had to lug all 3 sets of batteries to the shop to charge. After reinstallation of the fully charged batteries I finally found time and fairly good wind conditions to short the wires to see if it will stall or as you seemed to be uncannily right as always there is no stall, only poor or useless turbulent winds. To my surprise when I shorted to the original lenght which is 1/4 the long wire used it flew just as happilly and the ammeter shot up to 5 amps instead of the measly 2 amps I was getting. I have reversed the whole wiring back to the original format and charging 2 X 12 V Bats. From yesterday till today for the first time I saw the Voltage of the batteries actually rise.

You have been right all along Flux, I had no stall, just bad wind. These days the wind has picked up and it seems to be fine, enough for my daily low power needs. The blocking trees are down too. Now to get on with my 6 feet blades to get more power in low winds. You have been a real help, thanks again.

SeanChan:>)