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GWatPE
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Posted: 05 July 2008 at 1:38am | IP Logged Copy link to clipboard   

Hi readers,

PS edit:3/12/08


An important consideration that should be noted, is that the capacitor coupling arrangements are charge pumps, and as such, these should not be left unloaded. An unloaded system, even if the mill is only producing a few ACvolts, has the potential to still produce hundreds of DC volts on the output over time.

Due care should still be taken and treat all connections as lethal.



I have helped Dennis with some recording of CRO outputs of an 80SP in star configuration at 350rpm.

I have arranged the pics as comparisons. 200uF was placed between each set of windings. readings were taken unloaded and supplying a 24V battery at a constant voltage. All vertical scales are 10V/div.

this pic is the unloaded output waveform without and then with capacitors before the rectifier from the star point as reference.


this pic is the loaded output waveform without and with capacitors before the rectifier from the star point as a reference.


this pic is the loaded output that the battery sees. This is between bat -ve and the winding. this is across the bridge rectifier.


The results show clearly the voltage gain. The loaded current at 350rpm increased from 3A to 11A with capacitors.

The capacitors do significantly reduce the cutin speed. This will allow a particular windmill with a high cutin to produce current at approx 2/3 the rpm.

cheers, Gordon.



Edited by GWatPE on 03 December 2008 at 1:39pm


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oztules
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Posted: 05 July 2008 at 7:43am | IP Logged Copy link to clipboard   

Gordon,

Nice to see some clarification of what happens. The best feature of this it to allow larger blades to take advantage of lower winds.

I guess that changing the capacitors values will allow fine tuning to get out of stall much like a resistor does,... but without the loss. This perhaps should attract more positive attention than has been attributed thus far.
It may allow others to avoid the gearing thing,if the prop size allows for a 2/3 compromise to achieve close to the same thing.

The non-linear response of the diode has been cleaned up quite a bit, this may help those who wish to track rpm via frequency. Usually diodes under load make so much hash, that filtering is very important/tricky. The input line looks clean enough to read with a normal digital volt meter. (freq range)... handy. Usually, once cut in is achieved, the meter goes haywire. (no filter).

All in all, thanks to you and Dennis for these results.

..........oztules

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Posted: 05 July 2008 at 10:56am | IP Logged Copy link to clipboard   

Gordon, when you say the current increased from 3A to 11A at what point in the circuit are you measuring this?
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Gill
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Posted: 05 July 2008 at 12:45pm | IP Logged Copy link to clipboard   

Gordon,
Certainly it implies an advance yet "The loaded current at 350rpm increased from 3A to 11A with capacitors" is of no benifit if the power drawn from the motor is 4 times as much at that rpm....

As commented with Brucedownunder's test bed, power OUT has no valid reference for comparison without an accurate power IN comparison.

Without that data I can only say the wave form is pretty, but does pretty charge batteries better?

Edited by Gill on 05 July 2008 at 12:56pm


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Posted: 05 July 2008 at 3:55pm | IP Logged Copy link to clipboard   

Hi Gill & KiwiJohn,

I think you will realize that I have in the past been critical about the effects of capacitors and windmill loading also.

The currents stated above were battery load currents. This means that at the 350rpm level, a F&P 80SP stator, is only just above cutin to produce the 3A. The capacitors allow the mill to produce a higher voltage and hence at the same 350rpm, more current, 11A, can be produced. I have not mentioned anything re efficiencies. I have merely pointed out that capacitors can be used to better match the windmill output to the load.

In this example, the same stator would cutin at a lower rpm with the capacitors. It is obvious that if this was a real windmill and not a test bench that more power would need to be extracted from the wind and this would result in a slower rpm and hence the current gained may not be as much as the test bed at constant rpm. This purely highlights a way of producing power from a lower rpm, without the need of rewiring. .. Gordon.





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Posted: 05 July 2008 at 4:53pm | IP Logged Copy link to clipboard   

Looks good Gordon! I dont have any problem with capacitors as I fully recognise the need to match source to load.
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Posted: 05 July 2008 at 7:32pm | IP Logged Copy link to clipboard   

Gill,
Perhaps we need to stand back and see what we have done here.

If we currently have a well matched system (blade diam and tsr to alternator), capacitors will have no benefit at all, and will only serve to stall the blades so that they cannot work at all.... so where to next?

If we wish to take advantage of low winds (as an example), we could carve out some 4m blades, with a tsr of around 5. This is easy to carve to get this tsr, and will be quiet as well.

If we did this, to get our 350rpm, we would need a 34 mph wind to get 3A out of the stator Gordon and Dennis were testing(@24v) ie 75watts. We would have available some 7000watts to play with at the shaft, so efficiency is not the problem.... cut in speed is.

Now we add the capacitors, now at 34mph, 350 rpm, we are getting 11A @24v . So we have gained some advantage. The capacitors were giving the "system" a marked gain. We still have 7000 watts available so power is a non-issue.

Now it is clear that this example is both unlikely and silly in the component match, but it gives an indication of how the cap loading effects performance.

In less extreme cases say 3m prop tsr 5, we get our 350 rpm @22mph. Without caps, we get 3A@24v (about 75watts), or with caps we get 11A@24v or approx 260watts. Now shaft power is about 1300 watts, so there is plenty to spare.

In this system you need either gearing to speed the mill up (messy and lossy), increase the tsr considerably (harder and noisier), add caps, or some workable form of mppt (or Maximiser).

In this instance the caps are the best practical course of action. We have 5 times the power available to use if we can, so efficiency is of no consequence. We have power to burn, just difficulty in getting the revs to use the stator effectively (matching it).

Thats where this capacitor system has some serious advantages to "no caps, higher rpm, smaller blades (to achieve those higher rpm), lower low wind performance (because we need smaller blades to get cutin)".

But, we can't use it to improve a matched system, because your concerns now take precedence. (where is the extra power coming from).

So I guess it is like everything else in the world, different horses for courses. In some cases it will be a clear winner, in others, will be burdensome.

One other advantage which seems to be available, is that the cleaner waveform should improve power factor some, and reduce circulating currents in the alternator, as the harmonics from rectification are reduced significantly. I am blindly guessing that with the improved wave form, efficiency will be better than original anyway into a rectifier/battery scenario (and it could be bollocks too... your "power in /power out" testing is required here)


Just my take on it, it has a place in the scheme of things I feel, particularly if you want more power from low winds by increasing blade diam, but without rewinding/rewiring the stator.



..........oztules

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Posted: 06 July 2008 at 12:14am | IP Logged Copy link to clipboard   

Gordon, otules,
The application is not jumping out at me right now.
I'll give it more thought later.
Certainly noting and applying such characteristics to our advantage is how things are improved.

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Posted: 06 July 2008 at 9:27am | IP Logged Copy link to clipboard   

Hi Gill,

If you already have obtained a match between the blades, the generator and the load, then adding capacitors may reduce output. I suspect this may be the case for hydro, or a vegy diesel, but I doubt this would be the case for a windmill. If you already had achieved maximum power across a wide wind power range, you would not need to build an electronic MPPT. .. .. Gordon.



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Posted: 01 September 2008 at 3:57pm | IP Logged Copy link to clipboard   

Hi all,

I am not sure how may windmill owners have tested the effects of capacitors on a mill in the wind. I know that Bryan has had success and Bushboy Bruce has not.

I have just tried 110uF and 220uF on my 100S in star. Power output dropped and more significantly mill rotor speed ran away at higher windspeeds. Power output increased with windspeed up to 5A output and then decreased to 0 with further increasing windspeed for both capacitors values tested.

I was wondering if anyone has recorded this problem as well.

I will test my machine in delta with caps when it stops raining to see if Bryans results can be replicated.

Gordon.



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Posted: 01 September 2008 at 4:20pm | IP Logged Copy link to clipboard   

Thats interresting Gordon. It's as though something was throwing the tuning out as the windmill RPM increased. Like some sort of canceling of the resonance, sort of thing, you know what I mean.

I wonder if the cap location is important, like connected across the F&P terminals or further away at the bottom of the tower.

Could it be something down the line from the rectifiers, like a different battery internal resistance to those used in the earlier tests.

Glenn

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Posted: 01 September 2008 at 10:02pm | IP Logged Copy link to clipboard   

Hi Gizmo,

This has been only a prelim investigation. This is the only way possible to do realistic testing on a mill in operation, ie add caps to mill at bottom of the tower before rectification. There is probably an LwC interaction. An engineer may have an explanation. The LC combination appears to prevent current flow above a certain frequency. The current returned to the battery load increased and then decreased as the mill slowed down. Very strange to see the currrent increase as the rpm decreased. When the caps were removed at the high rpm, the mill loaded normally to the full amps, so the load was not a problem. The emf diminished above a certain rpm. The cap effectively loaded the coil to a point that the output emf was below the battery voltage. I cannot explain why the mill rpm increased. maybe the current developed an emf in the wiring and this effectively unloaded the mill, like placing resistance in the line.

I want to test this stator in delta again with caps. I am sure the pole twisting has changed the output waveform from a pure sine wave. This will probably mean independent rectification of each phase and a cap across the winding, effectively across the rectifier. This will have to be on the mill head. Luckily there is plenty of room inside the yaw box.

I will not be able to use the chinese mill controller to do this. I will have to use a normal diversion load controller as mill and battery protection.

I have a heap of 470uF 180WV electro caps that I will back to back configure to be non polarised, approx 235uF. I will make some quick connects with flex to the stator. Solder or blue point connections will have to wait. I have zero loss type connects that will save me a heap of time doing mods with the mill lowered.

I was unable to do much today. Rain, and strong winds not much fun with live windmill testing.

High pressure system will kill the wind for a while, so OK to leave as is for a while.

I am still in 2 minds re caps. I will need to talk to Dennis about a series 80 to rewire, to allow me to direct compare previous testing he has done. I have seen an increase in power with caps. The test rig had much shorter wiring runs. It may be that the wiring and component placement may be critical aspects of a successful use of capacitors on a windmill.

This is likely the tip of an iceburg, so I will press on.

Gordon.

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