Electronic braking

[Murlin]

Howdy folks, I had a question concerning shorting your turbine to slow the blades.

Would it be possible to use an alternator for speed control without frying the stator?

I wouldn't be trying to stop the rotors, just keep the speed under control up to a point.

Like 50 MPH winds, keep the speed of the rotor to 30 MPH just by using the alternator.

Thanks for your time

Murlin

[Flux]

I assume you are referinrg to stall regulation.

Yes it is possible to stall the blades to keep speed down, but you will need a very powerful alternator. With any of these types of speed control you need a backup scheme to prevent disaster if you loose load.

Provided that you can be sure to stop the blades under any circumstance stall regulation is perfectly possible. It is most commonly used with line connected induction generators but can be done perfectly well with battery charging schemes but expect to use about twice the magnet and copper in the alternator. You need the alternator stiff enough to effectively hold the blades at constant speed.

There are aerofoils specifically chosen to go into hard stall and that makes alternator life a little easier.

Flux

[Murlin]

Well you probably have figured out why I was asking this since I don't know that much....

I had a crazy thought....

I had quit working on my Turbine for a while because I wasn't sure If I wanted to mimic what was being done.  And since I still had a couple years before I would actually need it, I was exploring all the possibilities.

In one of your posts you spoke about hybrid turbines and when you suggested that by winding your stator with 6 in hand you could get a lot more watts, I got to thinking about all the problems with the current design of alternator....

I couldn't really think of any.....

So I started thinking on what would be a better one, and a thought occurred to me.

What if you could put 2 alternators in the air on the same pole?

No furling......less stress and such...

One stator would be wired to the low winds and one would be wired ot the high winds.

You could use a twin bearing design, that would allow you to extend the blades far enough from the pole as to use composite flexible blades and they would stay out of the tower.  You would want it up wind so it would track the wind easier.

These composite blades would be as stall regulated as you could come up with....(a lot of work has already been done on this)and be as light as possible as to start turning in the wind and making power faster.

You would also be able to stop the lighter blades easier.

All one would need is a capacitor bank,  a simple circuit, and a switch box.

You could switch back in forth manually if you wanted to, between the high and low winds and the non functioning alternator could brake the other.  Once the working alternator started producing a predetermined amperage, the capacitors would kick in and start breaking.

The backup would be a mechanical brake and to act like an emergency brake.

Since the blades are already stall regulated it shouldn't take as much as it would if they weren't to stop a runn away since hopefully the electrical braking being done by the other alternator would help decrease the work need to shut down the turbine.

The whole mess would be contained in a fiberglass shell that would keep the salt water and rain off it.

Anyways just a crazy thought....

Murlin

[altosack]

Flux,

I've heard you say before (to me ;-) that electronic stall regulation will take an extremely powerful alternator, and I have to agree and disagree.

If you let the prop/generator speed up to the nominal TSR in a 50 mph wind and then try to regulate it, yes, you will need a ridiculously large alternator. However, if it is continuously monitored, and kept below a reasonable power output (this means slowing the rotor down more and more as the wind speed goes up, until the rotors stall enough), a super powerful alternator is not necessary. A very good control algorithm is (and a backup system, such as furling ;-).

Realize that I have not built this, this is all numbers, so take it with a bushel of salt.

By the way, I have come across a reason that it may be very difficult to have a super-efficient alternator (more than the 70% you proposed as a first step in your excellent "matching the load" story), at least if it is charging a battery. It has to do with the ripple effect of the current/voltage, which is much higher than commonly assumed from knowledge about 3-phase AC alternators driving an AC load (and what I said about it a couple of weeks ago is not completely right). The higher your efficiency goes (as in low resistance in the stator), the larger the ripple is, until it actually reaches 0 output between surges.

I had been hoping to have an electronic control that only updated somewhere between 0.5 and 5 Hz, depending on the prop size and wind speed, but to get to high efficiency it looks like it will need to follow the ripple and update at at least 1 kHz or more (yes, Amanda, I'm considering something similar to PFC). Or, possibly going to a higher number of phases, but I'd rather not do this because I then either have to put the rectifier in the air or bring more parallel lines to the power shed; also, this idea would not work as an upgrade to existing designs.

I hope to put together some graphs and numbers to show what I'm talking about and present it soon so others can comment.

All the best,

Dave

[Flux]

Murlin

You seem to have some of the same thoughts as Dave (below if this turns up where I intend).

I am not sure how you intend to operate the 2 machine idea. Normally the small machine is designed for cut in speed and produces power in light winds. In higher winds a big machine with a lower pole number takes over and allows the prop to operate at higher tsr to extract more power from the better prop matching. The large machine is big enough to hold the prop in stall up to cut out speed.

This is normally with a grid tie induction generator system.

I haven't worked out if you are proposing to increase speed to capture more energy or to run the two machines at basically the same speed. I am not sure what type of machines you are proposing when you mention the capacitors.

If you are proposing to use one machine disconnected and capacitor braked to hold the other one then I see serious problems but without fully understanding the idea I will not comment further.

I originally thought you were charging batteries, not grid tie.

Flux

[Flux]

Dave

"If you let the prop/generator speed up to the nominal TSR in a 50 mph wind and then try to regulate it, yes, you will need a ridiculously large alternator. However, if it is continuously monitored, and kept below a reasonable power output (this means slowing the rotor down more and more as the wind speed goes up, until the rotors stall enough), a super powerful alternator is not necessary. A very good control algorithm is (and a backup system, such as furling ;-)."

Yes this is true. To some extent this is how most machines work. If you consider what Dan is doing, his machines are fairly well stalled at furling point and the brake switch will stop them and hold them. If he tied the tail so that it wouldn't furl the alternator would loose control in a high wind and the brake switch wouldn't stop it until a lull in the wind.

He is already using more powerful alternators than most to keep in stall over the working range and he is furling early. To take this stall regulation to higher wind speeds needs a much bigger alternator.

To effectively stall you need to keep the speed increase small with increasing wind speed. that needs a large alternator with low internal resistance.

Once you have that powerful efficient and costly alternator you can work wonders. you can track it at peak power and extract several times the power of a conventional machine and you can still drag it back into extreme stall when your batteries are charged and only need a few hundred watts of dump load for a machine with rated power in kW.

You are right that an alternator driving a rectifier to charge a battery will need to be bigger than one on sine wave load for the same efficiency.

Originally I thought you were worrying about ripple in the output current, now I suspect that you are thinking of the high peak to mean current in the windings as a result of the rectifier forcing commutation over a small part of the cycle with higher I^2R loss.

Going to high phase numbers will reduce ripple in the output current ( no importance) but will reduce the winding conduction angle and make the conduction angle problem worse.

I really don't follow your worry about an electronic control having to update at a high speed, you young ones make life difficult for yourselves by worrying about things that we never considered and never presented a problem.

All generators produce torque pulsations but with the exception of single phase it is very small and swamped by the inertia of the machine and drive .

Flux

[Murlin]

Flux,

Yes I was wanting to do what Dave was talking about.   I don't have the slightest clue how to use an alternator for a brake, I just assumed that you would have to have some capacitors and a circuit of some kind.

The twin alternator design would run the machine at the same speed and just switch over to what ever alternator needed because of the wind speed.

Where I live, the winds about 50% of the time were 5-10 MPH.....

This wouldn't produce a lot of power but it could charge the batteries.

So you are saying that you can not disconnect one of the alternators and use it as a brake?

Well rats...

Murlin

[Flux]

Now I understand what you are wanting to do. The capacitor bit caused confusion as it is normally used to stop induction motors, sometimes very violently if you have to stop something in a hurry, but it dissipates lots of power in the motor and has to be short time only.

I get the impression that you want to use a small alternator for normal use and use a second large one as a brake in high winds.

This is perfectly possible but you will not disconnect it and you will not add capacitors. You can use the big alternator with a cut in speed at near full rating of the small one and either dump the power into your battery or divert it to a dump load. The alternator must be loaded with fairly optimum load so that the excess power is developed outside the alternator, not in its windings.

If you want to use the total power for battery charging the scheme has little merit over using the big alternator alone and matching it better. To make the big machine cost effective it would better be of the iron cored type and that means that you have to contend with cog and iron loss of a big machine in low winds.

To use the little machine effectively it would need to allow the prop to track wind speed in lower winds and in high winds it would be inefficient and would be best disconnected.

If you want a reasonable battery charging performance in lower winds and want to use waste heat without further battery charge in high wind then the idea makes more sense. Choose the small alternator to do the battery charging up to perhaps 20 mph and bring the big machine in hard to hold the small one at full charge without overload. The big one will need to be a monster in relation to the nominal battery charge full output.

If you want optimum heat out you will need the big one to track wind speed and you will need series resistance or reactance to protect the battery charging one.This will need an even bigger machine to hold the blades down in very high winds without the aid of stall.

If I had to do this I would seriously think about a dual rotor for low winds and an induction generator gear driven for the hold back, with capacitor excitation (unless you could grid tie it)

The gearbox will be detrimental to the low wind performance and will add cost and trouble but will keep the brake alternator to a manageable size.

You are a mechanical sort of chap and you might be prepared to use a clutch to let the gearbox engage just before you bring the big machine into operation.

Yes possible but far too complex and expensive for me.

Flux

[altosack]

Flux,

I have the problem of having been pretty much of an expert in another field, now I am coming to this one trying to run before I can walk. Well, I have a bit of experience in solar electric systems, but little in hand-made wind generators. I'll take your "young" comment as meaning young to this field, and I kind of like to have some things difficult for me, by my own making or not.

Anyway, I'm attacking the "matching the load" thing pretty much solely to reduce the size of the alternator (compared with DanB's) without reducing the output and letting it retain better output in higher wind speeds. Not high wind speeds, just good to 25 mph or so, and levelling off after that to as high a wind speed as reasonable. By this I mean I'll take what I can get, but I will not increase the alternator size in order to get it; there's just not enough energy/month available up there anyplace where I might consider actually living.

What I meant about the electronic control updating quickly was to flatten out the peaks. Yes, I'm worried about the torque ripple, not the output ripple; maybe you're right that this is not a problem, but I think it might be as the alternator impedance decreases. More on this later.

I have not yet resolved where my compromises between efficiency, smaller size and cost, robustness, reuseable components, and ease of building are going to end up.

Dave

[Flux]

Dave

You are right that you can extract more power from the same size alternator for a given temperature rise by matching the load. I think Dan's alternator is big enough to let you do this very well at the power level he is achieving.

If we took his example with the same cut in and let the volts rise with speed with a buck converter it would produce more power in the same wind with much less loss in the stator. For the same temperature rise the power into the batteries would probably be about 3 times and at only marginally higher wind speed.

The limitation to output and wind speed will be alternator speed and noise. If you are used to commercial machines that probably means running at 3 times the speed that Dan does. By Dan (and my standards) that will be noisy but not by commercial machine standards.

As the matching becomes better, you reach the same output in lower wind speed and if you want to push things to higher wind speeds then you will need the bigger alternator. To achieve the best possible efficiency then again you need a bigger alternator.

If you just want slightly more power, modest speed and noise and a very safe temperature rise, then that size of alternator will be adequate as long as you furl early.

The simple truth is that a machine that matches the prop well without electronic conversion and running clear of stall is running at very low efficiency. You can not reclaim the internal energy loss and you will benefit little from power matching.

As Dan's machine is pushed well down into stall it is not well matched to the blades in higher winds it is already powerful enough to benefit from load matching.

To take the thing to high efficiency from those blades in a 30mph wind would need a far bigger alternator, but how often do most of us see 30 mph winds. It's better to furl early and save a lot of cost and weight.

I hope this helps you get things in proportion.

Flux

[Ungrounded Lightning Rod]

If all you're doing is trying to get some more power out of the alternator at high speeds, you can get a first-order approximation by doing a delta-Y switch.

Y is good for easy start, low cutin winds, and efficient generation at low speeds.  Switching to delta at some high wind speed drops the voltage (allowing the mill to speed up and reducing blade-stall losses) and lets you bank a tad under twice the current for a given amount of stator heating.  This is about as good as switching between two alternators with different windings, but without doubling the amount of magnetic material and copper wire you need to buy.

Delta-Y can be accomplished with a few relays and a little electronics to detect the speed (from the frequency of the genny output).  It can be powered directly from the genny (paying the relay pull-in current with a bit of the increased output current).

There are articles on it elsewhere on the board.

Not as good as a max-power-point tracker, of course.  But a WHOLE lot cheaper, simpler, and more reliable.

Getting a twofer in high winds might be worth chasing with a delta-Y switch.  If you really need the additional few percent of power beyond that you could get with a tracker, you'll probably end up with as much charge in your batteries and more money in your pocket if you just make the mill a slightly wider.

Wind is free.  "Good enough" is cheap.  Chasing the last few percent is expensive.

[Murlin]

If all you're doing is trying to get some more power out of the alternator at high speeds, you can get a first-order approximation by doing a delta-Y switch.

What I want to do is make the most power I can.

I was thinking of wiring my stator 6 in hand, ...6 in hand would give me 5 KW's on a 20 footer?  But it would be running below cut in half the time.

I could divert the excess to a dumpload and perhaps run a 3-phase motor or a welder.

Murlin

[Murlin]

Ya, if you have to go to all that, I guess it would get out of hand pretty quick.

If I wire my 20 footer with 6 in hand, would some sort of a variable pitched blade help to extract some power in the lower winds?

If the TSR was higher to start with and in 5 - 10 MPH winds would turn faster and start charging the batteries?

Then the centerfugal force would flaten the blades out and it would turn at the proper TSR.

Thanks for all the input,

Murlin

[Flux]

In the end it depends in what form you want the energy in high winds.

If your batteries are going to be full and you want the excess energy as heat you can use heaters in series with the ac lines. This will keep you at a similar power level into your battery but the machine volts will be able to track wind speed and progressively more power will go into the heaters.

If you track the power you loose the option of stall regulating, so you will have to furl or spill power in some way or accept a monster alternator.

If you match the alternator for high winds, pitch control will not help you in light winds. If you want to use pitch control,it will help you control excess power in high winds and it may possibly improve the power match a little, in high winds before you start to spill power.

If you want to optimise your alternator for high winds then you will need a boost converter for low winds, but even without it you will be cutting in more often than you might think.

Star delta is a sort of compromise solution and is certainly worth considering. With a big machine I suspect you will have to more or less accept star on low wind days and delta on windy ones. For small machines it is fairly satisfactory to keep changing from star to delta, it's a bit rough but you can live with it.

For a large machine the step from delta back to star is violent and I wouldn't this happening frequently ( as it will on many days unless you take steps to avoid it)

If you are happy to accept that you will be in the wrong mode quite often, it is worth considering. It will let you get far more output from higher winds for the same stator temperature and you can still have good results in those steady low wind days.

The control is stable if you use speed as a sense signal. The clanging contactors are a bit of a mess and that is another reason not to change over too often.

I did try on a 10 ft machine for a few days but changed to a boost converter and never looked back.

By all means try to extract more power up to 30 mph or a bit more, but I think you will find it futile to try to hold things down in winds above this without some form of furling or pitch control.

[stephent]

Looks like everything is a bit of compromise, gain here, lose there.

@Flux--anyone ever do the heaters inline and caps inline too at the same time?

Just wondering.

Seems the caps would let rpm go up without much loading in low winds--the heaters would take over as amps came up with rpm/wind speed rises.

Would take more then a bit of fiddling with it to get the right amount of inline resistance and cap reactance, but each wind genny is unique anyway.

But there's still that old bug-a-boo of heat in the stator.

What kind and temp rating of wire does most use for winding the stators?

Looks like maybe just regular old motor winding wire is too low a temp rating.

And then there's still the problem of the stator "holding-together" stuff --resins, heat, etc.

Looks like the whole subject is still in a state of design and seeing what will work well or just OK.

Looks like we just gotta repeal OHM's law--I^2 R....E^2/R...EI

[Flux]

The capacitors in the line is a way to match heaters for direct heating. If you want to charge batteries and gain extra heat with line heaters don't use capacitors.

Most winding wire has a temperature rating of 180 or 200 deg C. I strongly suspect that many are running well above this at the centre of the coils. Wire grades other than polyurethane ( solderable) die slowly above the maximum temperature and failure will not occur until the charred mess actually shorts out at one point. With low volts you may run in a more or less burnt out state for a long time.

There are higher temperature rated wires of the mineral insulated type but this doesn't help. There is no resin that I know of that can run continuously at 200 degC that has any strength.

Polyester of the boat building kind, for obvious reasons, doesn't normally have temperature limits quoted. Polyester electrical resins are normally rated for about 140 C. Most likely all are fairly similar.

Standard epoxies are generally pretty soft at 90 C. Electrical potting epoxy such as 3M Scotchcast are rated at 130C.  Special motor VPI epoxies can run at 180 C but are intended with slotted cores and may not be that strong as a self supporting mass at that temperature.

I have never seen figures for vinyl ester but it is generally claimed to be better than polyester.

The fact that resins can't manage the same temperature as the wire is not really a problem if you keep the wire below 200 C at the centre of the coil. This will mean that the outer part of the coils is nearer the limits for vinyl ester. There is a lot of temperature difference between the centre of the coil and the surface.

When you think about this,it is not surprising. Normal industrial alternators normally run at 1500rpm+ or 3000+ , so to squeeze the same power from a similar size alternator at up to 1/10 the speed is asking almost the impossible.

The smaller end of the high speed machines are not much over 80 -85% efficient at full load into a resistive load. Use rectifiers and they are worse. Now bring the speed scale factor into the argument and you see why I keep saying that to extract high power from a small alternator in high winds means size and cost.

If wind generators ran like their industrial cousins at full load 24 hrs a day life would indeed be difficult.

The aim with wind is to achieve the highest efficiency in low wind (which industrial machines are never asked to do), have a power out proportional to the cube of rotational speed and produce maximum power at a small fraction of the speed of the industrial machine at a size and cost that makes it viable.

Absolute efficiency in high winds is not so important as there is a lot of power available but it determines internal heating and the speed at which you loose control of the prop.

That is why I say it is futile to try to make a machine that will capture above 35 mph winds without furling and still produce power with winds below 10 mph.

[SamoaPower]

"I strongly suspect that many are running well above this at the centre of the coils."

"There is a lot of temperature difference between the centre of the coil and the surface."

Agreed.

I believe the main reason that exacerbates this problem is the rather haphazard way that many coils are wound. Since heat flow from the center to the surface is by conduction, any dead air space (a poor thermal conductor) between adjacent turns will increase the temerature gradient. Winding density is important.

I am currently investigating ways to improve coil density. There is nothing new or inovative about this, just applying simple principles to the axial flux coil shapes. I can now achieve copper densities of about 92%. I have an additional requirement that the coils also serve as structural elements of the stator. No casting for this boy.

The target goal of heat dissipation is to have the heat reach a surface where it can be carried away by convection to the surrounding air. I find it ludicrous that the current convention is to embed the heat producing elements (coils) in a thermal insulator (resin), particularly with the number of failed stators we hear about.

"There is no resin that I know of that can run continuously at 200 degC that has any strength."

JB Weld "claims" a continuous rating of 260C and a short term of 315C. They say nothing about remaining strength at these temperatures.

"The aim with wind is to achieve the highest efficiency in low wind (which industrial machines are never asked to do), have a power out proportional to the cube of rotational speed and produce maximum power at a small fraction of the speed of the industrial machine at a size and cost that makes it viable."

Yes, difficult indeed.

I might add, to also stay together for a reasonable lifetime.

[stephent]

I have been wondering if "painting" each coil layer with polyester/epoxy (JB Weld is slightly magnetic--cogging) would help get rid of a bit of heat. The small air spaces between each wire won't allow much thermal conductivity opposed to a solid across or to the outside of the coils.

Or even soaking the entire coil in varnish or something for an hour/day or two might help get the heat out of the coils. Allowing a few days/week of drying time after of course.

Something should work--geez 2 or 3 (4?) in hand windings of #14 or so of some of the stators built here should stand putting out quite a bit of power for days without cooking off, even though several seem to be a bit past the 700cm per amp ballpark.

[SamoaPower]

I've been doing just that on my latest coil test windings since I also want to achieve structural strength in the coils in addition to better heat transfer.

I'm using eight in hand #14 square 200C wire and am getting winding densities of about 92% (the square wire does have a corner radius). With this density, soaking doesn't work well so I'm applying the bonding agent during winding. Also, an air-dry agent may never set up.

I've tested 5 epoxies and found that JB Weld gave the best bond to the wire insulation and I suspect has better thermal properties because of the added metal particles. I was curious about your statement of JB Weld being slightly magnetic so, just now ran a test with a neo and couldn't detect it. With the small amount needed to bond a high density coil, I doubt it's an issue.

As long as you don't cast the coils in resin, cooling should be about the best obtainable, particularly if you use forced air as I intend to do.

[Flux]

yes impreganting the coil is standard industrial practice. Normal varnishes and impregnating materials are not desperately good thermal conductors, most are developed for high voltage. At the low voltages other things may well be better.

I hadn't realised the claims for JB weld, the version available here is not very inspiring in other ways and I haven't considered it. If it does have any strength at 200 C then it may be a good material especially if it has iron particles which should help heat transfer. I really can't see any problem magnetically but that would have to be confirmed.

I have never really bothered much about this heat problem as I have no place to fly very large machines and the things I play with have no stator heating problems when sensibly matched to the load. 2kW from a 10 ft machine doesn't seem a problem but problems likely increase drastically with prop size.

If you really manage to get things to run reliably at class H or worse then I think you will seriously need to think about the magnet temperature.

Flux

[SamoaPower]

You bring up an interesting point about magnet heating. Is there an inherent mechanism, during operation, that produces a rise in magnet temperature? Or, is it simply radiated absorption from the hot stator due to proximity?

In any case, forced air cooling in the gap should mitigate the issue.

[Flux]

The main issue is heat from the stator. There may be a secondary issue of induced current heating from flux ripple. Without iron cores I suspect this is a non issue, but small effects become more serious with size.

I agree that air cooling will be very beneficial. Larger air gaps and a reflective coating on the magnet rotors may also be worth considering.

High temperature grade neos are very much better and may be the way to go.

Unfortunately the strongest demagnetising field occurs at full load at the same time as maximum heat. The standard grade will likely start to show trouble at about 80 C when subjected to maximum armature reaction.

It should be possible to keep the magnet discs at a reasonable temperature, I am not sure what the thermal conductivity of magnets is like. All failures I have heard of so far have been from physical rubbing.

You are being quite modest with your expectations and I seem to remember you are looking at reasonable load matching so i really don't expect you will be any near class H temperatures.

It is those that bog things down at constant volts or try to hold without furling at high wind speeds who will have the serious heat.

Flux

[stephent]

We talking about the same JB Weld (I use the "quick" type sometimes too) that is for engine block repairing, etc? Blackish gray color when mixed?

If so--it does have a bit of magnetic properties.

Just put some in the next coil winding or coil center in the next coil you wind and hold it above a spinning rotor with magnets, etc..

You can feel the "thumping"/cogging in your hand if you hold the coil above just one rotor very easily.

It also brought up the voltage from the same coils I had in test--about 20% or so.

Center was maybe 40% filled and stuff was all through the windings when I wound it.

Came out hard as a rock and ready for testing--no tape--no super glue, etc, just JB Weld around/through and inside it.

Used to use plain old cheap finger nail polish (wifes stuff she didn't like the color of) for coil winding (ham radio) but it's messy and hard to explain why ya have it on your fingers the next day--hi--hi

But it does make a purty redish or pink coil!

Always wondered if the super glue was reacting with resin when it was cast--to the detriment of the casting.--??

Some of the stuff used to hold other stuff together sometimes don't play well with each other, I have found.

[vawtman]

Its fun to watch it crawl around the mags.Where are you going with this Stephent?

[SamoaPower]

Yep, same stuff but I only tested a small amount cured on a copper strip, perhaps .005" thick. Found no attraction to a neo. I guess your larger quantity showed up better.

The way I would use it, if I decide to go with it, is just a thin film between coil layers to bond it together and none in the center. With the square wire, the layers are very even and tight. I doubt if the film would be more than 2 or 3 mils.

Thanks for your comments.

[stephent]

Watch it crawling around mags?

Don't follow that exactly--but then again, I ain't the sharpest knife in the drawer either.

Not going much of anywhere--except thinking about using it (JB) in the 20 mag/coil 2 phase I have in the works. Kind of looks like what you are doing--but thinner stator. JB for all of the coils, to get them to hold together and maybe get rid of some heat better?

Maybe use resin/glass fiber for the bulk of the stator, but just JB around the coil itself. Maybe leave the center fairly open for air circulation.

I'm going to look a bit harder at the slight cogging first though.

But I do know JB will hold up very solidly to engine heat --approx 180 to 205 deg F. for quite a while. I've done several engine "repairs" over the years and have drilled and tapped it too.

[Flux]

I am sure there will be no magnetic problem using it between turns of a coil, even with round wire.

If it does increase output with large quantities in the centre of the coil, you may have to try some experiments. I am sure with it finely divided there will be no eddy loss and the hysterysis loss is likely to be very small. Cogging as such is highly unlikely to be desperately bad and careful experiment with coil hole size will likely keep it low.

Dual rotors have a lot in hand at starting, there is really not a lot of point in starting in winds that produce nothing. Cogging alone is not a major issue unless it is very bad. Without significant iron loss if it turns at all it will start without problem.

I am not suggesting that you do this without investigation, but I would not reject the idea totally.

I am not sure how effective holes in the coils are at cooling with the normal radial air flow. If you can get better cooling with a thermal conducting material to bring the heat to the surface and also gain a little in volts and lower resistance it may not be a bad idea.

With the price of JB weld here I shall not be trying it for filling holes, but for filling gaps between turns it is worth a look at,

Flux

[ghurd]

JB Weld. Take a defective neo, JB Weld it to a piece of scrap steel. Be generous with the JB Weld!

The stuff crawls up and coats the whole magnet. Makes a heck of a mess. I'd swear twice as much crawls around as I put under the magnets.

There also was mention, a long time ago, that the flux could be shorted to some extent.

Interesting to see.

G-

[Murlin]

My two-fer idea might have been a bust, but this thread sure isn't.

Pretty good discussion, thanks guys...

I am thinking servo/encoder pitch control now.....

Gotomypc.com ??.....

Wouldn't really be that complicated. Would cost a little more,  everyone has a puter....

You could run the servo push/pull rod right through the drive axis and put the servo/encoder on the back...

Course the design of the turbine would have to change.

Put a wireless link under the hood and you would be good to go....

You could WYFI control it from any coffee shop on the planet.....

Safty feature would feather the blades to 0 pitch in case of signal loss.  An anemometer would feed the computer info for constant pitch update.

Man, that would be cool..not totally unrealistic either....

Murlin teh more crazy ideas....

[stephent]

It can surely be done they way you describe--it's just the heat dissapation  problem of the alternator holding the thing back Flux and others were mostly agreeing on.

One or the other alternator/generator trying to hold the rpm down will get hotter then heck under some conditions....burn..then the wind genny will certainly overspeed.

And then the other alt will cook off--blades go poof--etc..

I think Murphy lives everywhere above 20 ft up and comes down to ground level to visit often!

I wouldn't trust electronics as the only form of control...up in the air there are static discharges that will fry solidstate stuff in spite of the very best "lightening" protection you can buy....a lightening discharge 3 or 4 miles away can induce a lot of volts into wiring and punch through a circuit board or device.

Looks like furling is still required of some sort for fail-safe.

[Murlin]

Ya lightning can be a biach sometimes.

As far as the heat dissipation, with pitch control you could lower the TSR the higher the wind got, it would be simple to compile a Windows proggy for that.

You would just need to build a control board for your pc.  And the alternator wouldnt have to do much braking, let the blades control the speed.

And in case of loss of feedback or servo power, a manual spring system would feather the blades to ZERO pitch and they would hardly spin at all. So it couldn't over spin and fry.

Using an encoder you could have precise control.

When I say 0 pitch I mean turning the edge of the blade to the wind and cut it like a knife.

With forced air going across the stator, you might be able to keep the temp manageable.

I think the choices are either furling or pitch control.   If you have control of your blades, I don't think you would need to furl.

Could be wrong, it wouldn't be the first time

Murlin

[Murlin]

Ya lightning can be a biach sometimes.

As far as the heat dissipation, with pitch control you could lower the TSR the higher the wind got, it would be simple to compile a Windows proggy for that.

You would just need to build a control board for your pc.  And the alternator wouldnt have to do much braking, let the blades control the speed.

And in case of loss of feedback or servo power, a manual spring system would feather the blades to ZERO pitch and they would hardly spin at all. So it couldn't over spin and fry.

Using an encoder you could have precise control.

When I say 0 pitch I mean turning the edge of the blade to the wind and cut it like a knife.

With forced air going across the stator, you might be able to keep the temp manageable.

I think the choices are either furling or pitch control.   If you have control of your blades, I don't think you would need to furl.

Could be wrong, it wouldn't be the first time

Murlin

[Murlin]

Hrm..... how did that double post happen???

Grrrrr