Using Caps on a Wind Genny

[ruddycrazy]

Hiya Guy's,

           Over here in Oz we have a raging debate going over the use of caps on a wind genny. I used on my setup 2 off 470uf @400 volt electo's, put them back to back to make them unpolarised then put 3 sets of them on my genny input 1 set set on each phase. Before I used the caps the best I saw on my 24 volt shed array was 10 amps out of the genny, then I put the caps in and sure enough when the next gust of wind came along I saw about 18-19 amps @ 25.8 volts. Gordon (GWatPE) is a good friend and cameup up to my farm last sunday and later went home and replicated my setup. The following link is to a backshed post where further down the page Gordon shows the increase in a more technical nature.

http://www.thebackshed.com/Windmill/FORUM1/forum_posts.asp?TID=1138&PN=1&TPN=4

Now the big question is how would this setup go on other types of Wind Gennies as if it works it could mean a greater input from a genny at little or no extra cost.

Some good advise has come out and that is if you try this make sure your system has the furling setup correctly as if the caps do fail the genny will overspeed and self destruct.

Cheers Bryan

[Flux]

Alternators are affected by the type of load. Armature reaction ( the effect of the magnetic field from the current in the windings) affects the main field. Inductive loads result in the armature reaction being demagnetising and reduces current output.

In theory resistive loads only distort the field, but as saturation normally occurs somewhere there is usually still a demagnetising effect. Capacitive loads produce a magnetising armature reaction and the increase in field will result in increased output, although the inductive reactance is still effectively in series you will benefit from the higher initial emf.

Air gap machines with no iron will have a small armature reaction and will never reach the reactance limiting stage. The effect of adding capacitors to the air gap axial machines will be no significant gain in magnetic field and your stator has to carry the reactive current with more drop.

Use capacitors with iron cored machines especially those with seriously high leakage reactance and you will benefit. Don't bother with axial air gap alternators it won't help and may hinder.

The ideal solution for the F& P and other highly reactive machines is to include the capacitors in series with the windings. If you can achieve resonance with the inductive reactance the reactive component is neutralised and only the resistance remains. Not really practical for wind but it may be a useful dodge with hydro where you run at constant speed and can maintain resonance.

Flux

[oztules]

Flux,

whilst I understand your argument, your conclusion does not seem to be born out in real world testing.

These graphs would seem to indicate that a vast improvement for wind application is apparent with this style of high pole count alternator.

Here is the data of relevance as explained by the experimenter

"This is a comparison of before and after series caps on a 100S F&P in delta.

The comparison should be interpreted as the change in the ratio of the average of the F&P in yellow to the axial flux in purple. The F&P has 50% larger swept area.

Thge first graph is before caps with maximiser and the second shows the change in the yellow graph[F&P with caps], without maximiser. The ratio of the average of the data is the important detail."

"The ratio in the first graph is 1.33

The ratio in the second graph is 1.46

The caps provide a better increase in average power than a boost maximiser.

There is a significant increase in the maximum power output, by almost a factor of 2. This would be of more use in stronger wind conditions.

A combination of capacitors and boost maximiser will be looked at next.

This should give benefit at the top and bottom of the windspeed range.

More to come.

Gordon.

PS

The graphs are battery current vs time, for the same timing period. The wind conditions had changed, but the 2 windmills were operation in the same winds, with no wind shadowing and are only 6m apart."

===================

The yellow is the F&P, and the pink is the axial flux alternator used as a reference.... 6 meters apart

Faced with this result, I think your conclusion "Not really practical for wind but it may be a useful dodge with hydro where you run at constant speed and can maintain resonance."   is difficult to comprehend.

I would have thought an increase of that magnitude is worthwhile, and would certainly be applicable to wind. It also seems to stop the mill going into runaway at 10 or so amps... which alone is very worthwhile.

It seems to me that getting some improvement in some parts of the spectrum, and massive improvement in other parts is worth pursuing, stopping runaway and getting a vast improvement in power where non at all was available before (because of reactance limiting at 11A) is a worthwhile gain, The caps seem to  turn a very average device into a reasonable device.... (I'll stick with axials myself however)

........mystified with your conclusion here

........oztules

[fungus]

"Faced with this result, I think your conclusion "Not really practical for wind but it may be a useful dodge with hydro where you run at constant speed and can maintain resonance."   is difficult to comprehend."

As far as I see it, that comment was directed towards using capacitors in series with the windings?

[oztules]

Of little relevance to the above......

It is interesting how well the booster was operating in graph 1 (it cuts off after 2A I think). At no time was the power output below the axial.

In graph 2, the F&P without the booster fell below the axial on many occasions (I assume lower freq hurt the capacitive coupling). I wonder if greater than 1.46 would have been achieved if the booster had have been there to hold the lows at a higher level.

........oztules

[oztules]

Hi Fungus,

The second graph is with caps in series with the windings..., and without the boost converter.

.........oztules

[Flux]

Sorry I haven't been following what you are doing in Australia, the F & P is not available here so there is no interest in it.

I assumed from the description that the capacitors were added across the phases ( as in a power factor correction system). As I said there will be a large improvement with a high reactance alternator and if the gain in emf from armature reaction addition of flux if sufficient to allow you to change from star to delta will make a spectacular improvement as you are reducing the impedance by a factor of 3 ( including the resistive bit and that is where most of your gain is coming from).

In this case the capacitors are not resonant and are not removing the reactive component. With series capacitors in a star configuration you can at one frequency cancel the reactive component. It will work over a small range of speeds and even with speeds over the resonant value it will still bring the load power factor leading and will still give the same effect as the shunt capacitors. This may still be worth trying with wind but the capacitors need to be very large for low voltage systems and would probably need to be electrolytic back to back.

I would have doubts about the initial cost and long term reliability but if the gain is great enough then it may even be worth spending a large sum on non- polarised capacitors.

Some of these arguments will also apply to motor conversions, especially to those with low flux levels. If you can get away with less magnet you reduce iron loss drag and get easier start up, if you can increase the flux level with capacitors then you are on to a good thing but again all these schemes work far better at high voltage. The frequency of motor conversions will need capacitor values that are not really practical. At least the F&P has a large pole count and starts with a reasonable frequency so capacitor values are more modest.

Flux

[electronbaby]

It appears as if you are playing against the reactance of the feed line. It would be interesting if tests were done with the caps located at the turbine, and at the rectifier, however, the overall outcome will probably average out to be the same.

In these tests that are being done in Australia, what type and size of feed lines are being used? How long a run is it? in Ohms?

[oztules]

Check that link in Bryans comment. The waveforms are of interest. There are high voltages and frequencies involved with this style of stator, (50 something magnets apparently and 40 something coils) and I am just now beginning to suspect things other than power factors and inductive reactance difficulties are involved here.

There seems to be a genuine current conversion going on in the caps. I am wrestling with the theory that the gap in the square wave is possibly held open by the other two phases for a brief period, giving the cap time to accumulate some electrons, which get discharged a little bit later on in the form of higher current burst. There is an abundance of voltage in the coils. For a 24v system, the coils are up around 60v rms apparently.

I have no idea... but something is happening that is certain.... but still clutching at straws at the moment.

.........oztules

[Flux]

Ok I have read it briefly. He does say that the capacitors are in series so in that case there will be a resonant point where the capacitive reactance neutralises the inductive leakage reactance. At that point the current will be dictated by the winding resistance just as for an axial air gap machine and the characteristics should be similar. Without this those alternators become reactance limited and no matter how fast you run them the current will eventually become constant. The thing starts to curve over when R becomes equal to Xl. as Xl dominates the reactance rises with frequency and it goes into constant current mode like a bike dynamo.

If you can get things right then the alternator load will increase with speed instead of levelling off and if you can track that to the prop characteristic then you will gain enormously. I suspect that if the wind gets high enough and you go beyond resonance the capacitive reactance will be small and the thing will revert back to inductive reactance limiting and it might let the prop run away.

There will be plenty of volts flying about at this resonant point and it will be similar to a motor starting circuit for single phase. Watch the capacitor volts, at resonance you may go well above anything you expected.

If you get this right then you overcome the most serious disadvantage of these long pole iron core machines which were intended as synchronous motors and are not ideal as alternators.

Play with the capacitor values they may well be quite critical for best results.

Flux

[tecker]

The series Caps work while running caps around the same rating would not . You can see from the wave form what is hppening the voltage rises to a spike before leakage to the other cap in the series string starts and the combined charge starts to accumulate just before the current flow . If you put running caps in there they would discharge slowly and screw with the current flow lagging the current by 30 to 40 degrees . This spike and light discharge puts you up on voltage and current you can see the current as it flattens the sine on the backside .

[tecker]

Very good data and nice mod I assume those were both 230 mike electrolitics

[Ungrounded Lightning Rod]

Capacitors in series means the load is zero at startup and rises with speed (up to resonance).

Perhaps part of the gain is from getting the turbine out of stall?

I'd like to see the frequency or RPM versus wind speed for both configurations.

I'd also like to see how the genny, caps, instruments, and load were connected.  I wouldn't expect caps in SERIES to smooth out the waveform.

(Meanwhile my first attempt at a conversion will probably be putting some magnets into a variable-speed motor I salvaged from a Maytag Neptune.  I think I'll play around with caps to see if I can get more out of it or get it to run in a better mode, once I've gotten it converted.)

[zeebag]

You got a nice friend. Were those indeed 230 mike electronics?

[oztules]

The two 470uf electro capacitors are back to back in series to give a 235uf bipolar electro.

Whether this is the ideal value for this setup has not been properly established yet, seems to work well. I believe more testing with other values is yet to come.

........oztules