wiring 9C stator as 3 separate 3C gens?

[spinningmagnets]

I can't have a wind-gen where I'm at, but will retire soon, doing homework now. I am planning on casting a 3-phase stator with 9 coils, and having each coils 2 leads outside the casting for experiments with star/delta, and series/parallel...I am still learning.

An idea occurred to me, probably foolish. Load affects RPM's, this is shown by the need for dump load when battery is full. If less load spins faster, or faster near cut-in...perhaps using only 3 of the coils as a smaller gen will allow higer RPM's near cut-in?

During solid winds and battery at max charging, a surface-mount temp sensor on the stator could alert a circuit that begins rotating the use of 3-coil sets in the 9-coil stator to help cooling?

If less load allows higher RPM's in fluctuating winds, perhaps if using 3 coils when battery is near full could keep the RPM's higher enough to harvest a few more Watts than otherwise?

I am not in a position to experiment with this right now, its just a question for amusement and learning.

"Exaggeration is a million times worse than understatement" -Steven Wright

[wooferhound]

My instantaneous and unscientific thought is that, you will get the same amount of power and heat out of either arrangement. In a regular set-up all of your coils would be producing heat equally. In your second arrangement you would have three sets of coils, but each set is getting 3 times hotter but only being used 1/3 of the time.

Using only one set of coils is single phase and has cogging/vibration problems.

Bringing the wiring out for each set of coils and using the power separately is "Jerry Rigged".

[Flux]

An idea occurred to me, probably foolish. Load affects RPM's, this is shown by the need for dump load when battery is full. If less load spins faster, or faster near cut-in...perhaps using only 3 of the coils as a smaller gen will allow higer RPM's near cut-in?"

Don't follow this. Normally you need all the volts you can get at cut in. Up to cut in there is no load to affect anything. If you reduce the number of coils you will just not cut in in low winds ( assuming you have the design right in the first place).

If you try your trick with a normal winding it will only work in high winds. If you wind the coils with more turns to get a cut in in low winds with 3 coils they will have to have thinner wire so will get hot quickly in high winds. Assuming you can pull off the crazy trick of rotating the coils you will have the same heating and a complicated and probably unreliable mechanism to put up with.

What you may be able to do is use one winding of 3 coils wound with thin wire and lots of turns to get a low cut in speed, this will work in light winds. You could then wind the remaining 6 coils with thicker wire and keep their cut in speed at 12 to 15 mph. This winding would handle the high wind region.

Two snags,firstly you will need to get rid of the low wind winding in high winds or it will burn out or waste a lot of power when it is running inefficiently in high winds. No big deal, simpler than your original proposal.

The other snag is that in high winds you only have 2/3 of the winding space available for the high wind winding so you need thinner wire than desirable. Even so if you choose your turns right you get a far better match to the prop and you can still come out with a lower resistance than with a conventional machine wound to suit cut in and running stalled most of the way up the speed range.

It is difficult to keep these schemes absolutely simple and it is probably this lack of simplicity that forces people to accept the common stall operation. Nearly everything that makes some attempt at matching the load gives better performance but few seem prepared to even try it.

I had reasonable results with these schemes based on two alternators ( sharing the same magnets)but in the end it is much simpler to use the whole machine all the time and do other things to do the load matching. The higher you can keep alternator efficiency the better and only using part of it means starting with more magnets and copper.

Flux

[electrak]

I have thought about that abit too. I don't have much wind where I am now ( 3-5 mph mostly, high wind here is gusts to 30-35 )

Have 1 phase set for low winds 4-5 mph second 8-10 third 12-15

My other thought was to wind coils with increasing turns then retify each. I was thinking of using a high blade count for this or a VAWT.  

[spinningmagnets]

Thanks for the responses! Should I acquire a good wind site, I will data-log at the top of a pole, and copy a solid design that matches actual wind there.

I had thought I could do some experiments on a second turbine for fun, but its looking like many others have tried everything I could think of!

[TomW]

magnets;

I had thought I could do some experiments on a second turbine for fun, but its looking like many others have tried everything I could think of!

Likely true but, hey, it might still be fun!

I think folks usually respond in a manner more in line with not sending folks down dead ends while trying to get a working turbine figured out with the least amount of expense in cash and time.

You never know when an experimenter might have a "golly gee" moment and a flash of insight from a different angle.

I did lots of tinkering years ago when I first joined here. Lots of dead ends and things that did not work like I hoped but I would not discourage someone from trying the same things as long as they understood it might not work as they thought if they expected good results. Swapping in NEOs on tape drive motors is one. Either way its a learning experience.

If that makes sense?

Tom

[GWatPE]

I have also tried the switched winding path to attempt to match the alternator to the wind energy.  I had tried series parallel arrangements of coils in the same phase, as well as star/delta switching.  All these require some form of rpm sensing and relay type controlled switching of the coils, with some hysterysis and timing delays to extend the life of switching components, if using mechanical relays.  The relays tend to make a racket in gusty conditions.

At the end of the day, the lowest possible winding resistance and the alternator wound for a normal cutin at approx 2/3 of max rpm gives the highest practical efficiency.  The trouble is no output to a battery load at the bottom 2/3 of the mill rpm.

For the windmills that are not blade stall limited.

If you normally wind coils for cutin at 100 rpm, with a 300-400rpm top end. The alternator may have had an efficiency of 50% at the maximum power.  

This same alternator could be wound for cutin at 200rpm.  The alternator would now have an efficiency of probably 75% at maximum power.  This would translate for most mills of additional power to the load, as less is converted to heat in the stator, as the resistance is half for the same load current.  For a typical dual rotor AxFx alternator, say nom 1kW. an additional 250W could be available to the load at maximum power.  The power at the bottom rpm end, below this higher cutin rpm is recoverable with an additional external capacitor voltage multiplier arrangement.  This is easily made for a 3phase alternator, with some additional rectifiers and cap coupling to them.  The caps do not pass the full power of the alternator, but approx 20%, at maximum output power. For a typical alternator dual rotor, 12mags per rotor, 9coils, 3phases, 100rpm cutin required, approx 1000uF caps will do. AC rated caps are required, and best results are with at least 200VAC ratings, to handle the AC ripple current.

The higher alternator efficiency will reduce the liklihood of peak current coil failure.  

There is no rpm sensing, or switchmode DC-DC converter, and no relays. The arrangement is just in parallel with the existing rectifiers.  The inherant electrical characteristics of capacitor gives an increasing loading with mill rpm.  Once the mill reaches approx the 200rpm, the normal rectifiers add to the power output.  The multiplyer will vary the voltage gain automaticaally between the mill and the load.  As the windmill increases rpm, the voltage gain will reduce.  The AC voltage across the caps will increase until half the voltage from the windmill appears across the caps, when the normal rectifiers start to conduct as well.

The windmill may stall the blades at higher windspeeds, towards the point where normal furling would occur, due to the lower alternator impedance.  This will all depend on the load impedance.  The windspeed, and wind energy distribution at a location will determine the significance of potential power loss if this happens.

The capacitor multiplier arrangement is like an external electrical gearbox, with no moving parts, that can be tuned to the application.

One aspect to consider is what to do with the additional power.  If eventually a cap fails, usually goes open cct, the windmill will not become dangerous, but power output will just decrease at the lower rpm.  I have cap doublers on my iron cored windmill and I will incorporate them in my new 48V AxFx mill.  The winding phase resistance will be under 0.5ohms, and the windmill will not have startup stall problems.

Gordon.

[Flux]

This is much in line with my findings and in the end I prefer one efficient winding to various splits. The 2 machine approach can work if the low speed winding is fed via a buck converter so that the 1/3 winding still contributes its full amount in high winds.

I have had very good bench test results with such a scheme but the complexity makes it less attractive and few would manage to do it.

I disagree with Gordon one one point.

"This same alternator could be wound for cutin at 200rpm.  The alternator would now have an efficiency of probably 75% at maximum power.  This would translate for most mills of additional power to the load, as less is converted to heat in the stator, as the resistance is half for the same load current. "

If you double cut in speed you need half the turns, you now have room for wire of twice csa so you end up with 1/4 the resistance. That and the vastly improved prop matching makes a very big difference in the high wind output.

I used a boost converter to regain the low wind performance, the voltage multiplier approach should do a similar job but if I was going down that route I would design the alternator with many more poles to raise the frequency. If you can tolerate very large electrolytic capacitors and lots of them then it may be ok with a conventional low pole count axial.

Not having tried the capacitor multiplier I am not in a position to comment but if you are scared of electronics then the capacitor arrangement may be the way to go.

If you make these changes on a standard design machine watch out for other factors such as effect on furling, it becomes a different beast out of stall.

Flux

[Ungrounded Lightning Rod]

During solid winds and battery at max charging, a surface-mount temp sensor on the stator could alert a circuit that begins rotating the use of 3-coil sets in the 9-coil stator to help cooling?

Rotating the sets, rather than using them all, will HURT cooling.

Output power is the product of current and voltage.  For a fixed voltage power goes up with the current.

Resistive losses are proportional to the SQUARE of the current.

If you rotate your coils (and maintain the same load) you triple your current and multiply the loss power by 3 * 3 = 9.  The current is on 1/3 of the time so it's 9 / 3 = 3 times the average power dumped in the coils as heat.

So distributing the power over the coils evenly causes less heating than switching it among them, spiking it up and then turning it off.  A low constant current in the coils produces less heat than a varying current with the same average.

Now that's not QUITE what the current would be doing in a real machine with this switching system.  But it's a close approximation.  At a constant RPM turning off some of the coils would just turn off their current.  But the RPM is controlled by the mechanical resistance to the shaft's rotation, which comes from the magnetic field, which comes from the current.  Turning off some of the coils reduces the torque load, which lets the blades speed up, which raises the voltage, which raises the current in the coils, ...