Cooling loop in a winding.

[Timeless Turbines]

    What do you think of holding two feet of wire outside of the stator. When your in the middle of wrapping a coil, pay out two to three feet of wire then go back to finishing your coil. This wire could be twisted into a small spiral of wire, and would be outside of the stator with air blowing across it to help cool the stator.

Thanks for your input.
Larry

[joestue]

the increased losses would counter any gains.

[gsw999]

Better off drilling some holes in the coils maybe if your worried about overheating.

[Bruce S]

Better off drilling some holes in the coils maybe if your worried about overheating.

You do mean the backing plate right  drilling holes in the coil would be not cool 

Have fun!!
Bruce S

[gsw999]

Better off drilling some holes in the coils maybe if your worried about overheating.

You do mean the backing plate right  drilling holes in the coil would be not cool 

Have fun!!
Bruce S

I meant drilling through the centre of the coils , I take it this is not a good idea?

Gavin

[joestue]

embedding anythign inside the coil would be nightmare.

one possibility would be to wrap a flat heat pipe around the outside of the coil.
the heat pipe would then be bonded to a ring of aluminium around the stator, and a ring of heat sink fins wrapped around that.

certainly possible, but expensive.
There's a few companies that make 1 mm thick heat pipes, but they probably don't have 10 inch long .7 inch wide strips off the shelf.

[Bruce S]

Better off drilling some holes in the coils maybe if your worried about overheating.

You do mean the backing plate right  drilling holes in the coil would be not cool 

Have fun!!
Bruce S

I meant drilling through the centre of the coils , I take it this is not a good idea?

Gavin

I have not done this, but there has been talk in the past about drilling cooling holes in the center.
I believe, Flux and others can give a much better write up of it, but general consensus was that the cooling hole benefits did not out weigh the extra work.

Bruce S
 

[Ungrounded Lightning Rod]

    What do you think of holding two feet of wire outside of the stator. When your in the middle of wrapping a coil, pay out two to three feet of wire then go back to finishing your coil. This wire could be twisted into a small spiral of wire, and would be outside of the stator with air blowing across it to help cool the stator.

Thanks for your input.
Larry

I think it would cool the first couple turns near it and do nothing of interest for the rest of the coil, which will burn out just fine.

IMHO a better approach is just to not pot the outer portion of the coils that are not between the rotor magnets.  Dip 'em in wax to keep the casting compound from wicking into them, then gently melt the wax out after the casting is done.

Leaving them exposed to the air should cool, by conduction, the two half-turns where each strand of the arch sinks into the potting compound.  That's probably all you need.

[joestue]

    What do you think of holding two feet of wire outside of the stator. When your in the middle of wrapping a coil, pay out two to three feet of wire then go back to finishing your coil. This wire could be twisted into a small spiral of wire, and would be outside of the stator with air blowing across it to help cool the stator.

Thanks for your input.
Larry

I think it would cool the first couple turns near it and do nothing of interest for the rest of the coil, which will burn out just fine.

IMHO a better approach is just to not pot the outer portion of the coils that are not between the rotor magnets.  Dip 'em in wax to keep the casting compound from wicking into them, then gently melt the wax out after the casting is done.

Leaving them exposed to the air should cool, by conduction, the two half-turns where each strand of the arch sinks into the potting compound.  That's probably all you need.

somone on has already done an excellent job of that and posted it. i can't remember who it was.
he had individually potted coils

you're pretty much required to pot the entire winding due to environmental issues.

[kevbo]

It is not too uncommon to do something like this on motors and transformers.  On transformers they are called chimney windings.  Most automotive alternator and AC motor stators have a bit of  extra wire off the ends of the laminations partly for cooling  purposes... that is to say the windings are not "tight".   Power plant size alternators frequently have water cooling provisions in the windings.

A long loop is a waste.  Copper is a great heat conductor, (for the same reason it is a great electrical conductor) but you still need cross section to move heat.  Just make the wires on the outside of the coils a little longer, each different so they are not in one bundle.

These measures are done to get more power from a smaller/cheaper device, and to make it last longer, not so much to improve efficiency.  Given that stator burnout is a real concern with wind many wind machines, it may not be a bad tradeoff.

[Ungrounded Lightning Rod]

somone on has already done an excellent job of that and posted it. i can't remember who it was.
he had individually potted coils

They were essentially one-coil potted loops with mounting flanges and a couple connection posts made out of something like a bolt for interconnecting the coil.  Very little potting material around the coils beyond what was needed to pot and support them.  Assembled into a stator with lots of air circulation through the middle of each coil.  (Sides needed to be pretty much in contact with each other.)

Maybe somebody can hunt up the article.  Nice work and good pictures.

you're pretty much required to pot the entire winding due to environmental issues.

Why?  They should be OK if you put a "roof" over 'em so the air/rain/snow/crud flow only comes in horizontally and put a screen over the openings to protect 'em from flying junk.  If they get some rain, or even ice, on 'em they should just melt it off again.  The insulation, if not nicked, should also protect them from corrosion if you've got some salt spray or the like.

[wpowokal]

I have been reading this thread and started to reply twice but gave up, the idea is OK but there is not a lot of logic in it.

 But as to potting the whole stator for weather protection or not very much depends on the individuals environment, members of this board are believe it or not spread all over the world and what works for some may not for others.

Stators burn out when a builder ignores wiring capabilities, fail to set furling correct etc, or things come loose and a rub occurs.

Alan

[Flux]

There are occasions when you have good air flow when you can wind the coil to expose more surface area to the cooling air. it works as long as you can get intimate air flow to the extra copper without adding too much to the turn length and increasing the resistance.

In the case of many iron cored alternators the current is determined by reactance rather than resistance so it doesn't matter if you add some extra length of copper.

I assume we are looking at the axial air gap alternator here, in which case the thing is resistance dominated and adding much in the way of extra copper is going to make things worse.

There is very little predictable air flow over the coils of this type of machine unless you make a very definite attempt to do something different.

Making holes in the centre of potted coils seems to be proposed regularly but I am not aware of any test confirming the benefit or otherwise, I seriously doubt that it will make any difference without clever fans and ducting.

ULR suggested not potting the ends of the coils at the outside where they are most likely to see some air flow and if you don't need the potting for weather protection this is likely to be the most effective.

Making holes in the magnet rotors in the correct place and not potting the magnets so that they act as fans seems very sensible and you will induce some radial air flow over the stator. If you don't need weather protection you could combine this with leaving the outer end loops unpotted and you could even spread the end turns a bit.

How much any of this is worth doing is dependent on how you want to run your stator. There is no big issue until the electrical efficiency falls to somewhere near 50%, once you start dissipating more energy in the stator than you use then heating does become a big issue. The only real virtue in an inefficient stator is that it will match the blades better and produce less stall without external added resistance and as such it becomes a cheaper method of direct matching a machine.

By messing about with extra cooling you may be able to maintain power without furling to a slightly higher wind speed but as the power in the wind increases as the cube law you will only hold it off for a few mph. It may make the furling less critical with a bit more in hand for the winding temperature.

I am not the best person to advise on this matter as I have never really tried to devise methods to dissipate kw from the stator. I am sure there is scope for improvement but I see problems doing much good in wet climates especially with higher voltage machines, the potted stator is protected from wet. If you want to get away from potting then you really need an enclosed machine and that can be done more easily with a radial design.

If you find a way to match the load then this issue mostly disappears and you can get 3 times more power out of the same stator without dropping below 60% efficiency and the heating problem is very much less.

As to the original proposal with long loops of wire sticking out then it is a no go area but there are practical methods that can be employed to get better cooling so keep looking at new methods.

Flux

[jlt]

Or maybe  make the stator from a hollow aluminum and run water threw it.I tried spinning a aluminum plate between my rotors and it made lots of heat.  There should be a rotating coupling that would handle two lines somewhere? And insulate the lines coming down the tower with expanding foam . Just having a brain fort.

[joestue]

you trying to make a hot water heater?   

[Bruce S]

Or maybe  make the stator from a hollow aluminum and run water threw it.I tried spinning a aluminum plate between my rotors and it made lots of heat.  There should be a rotating coupling that would handle two lines somewhere? And insulate the lines coming down the tower with expanding foam . Just having a brain fort.

I'm pretty sure you succeeded in making an eddy current device by placing the Al in there.

Could be wrong.
Bruce S

[jlt]

Yes it an eddy current device. changes motion  into heat.No electricity involved.

[Bruce S]

Yes it an eddy current device. changes motion  into heat.No electricity involved.

Neat, how well did it work out?

[TomW]

Yes it an eddy current device. changes motion  into heat.No electricity involved.

Except eddy currents are electricity flowing in tiny loops in the Al.

Just to clarify.

Tom

[Ungrounded Lightning Rod]

Yes it an eddy current device. changes motion  into heat.No electricity involved.

Actually there IS electricity involved.  But it's all running in loops inside the stator.

That's also why winding your coils out of tubing and pumping cooling water through it is not a good idea - unless you're mostly after hot water.  Expanding the wire into a tube produces lots more path for eddy currents than leaving it as a thin solid cylinder.  Most of your power goes into heating water.

[joestue]

Expanding the wire into a tube produces lots more path for eddy currents than leaving it as a thin solid cylinder.  Most of your power goes into heating water.
[/quote]

I wouldn't go that far, but of course it depends on the size of the tube.

in the case of 1 inch wide magnets, 1/4th inch tubing is asking for trouble, but it wouldn't be that bad. (maybe 5,10% losses?)

However, take 1/4th inch copper refrigeration line, its only equivalent to a 7 Awg wire, but its the same diameter as a 2 awg wire...

oh, and try pumping water through capillary tubing.. ain't going to happen.

[Ungrounded Lightning Rod]

Making holes in the centre of potted coils seems to be proposed regularly but I am not aware of any test confirming the benefit or otherwise, I seriously doubt that it will make any difference without clever fans and ducting.

Like by putting holes inside the magnet ring in ONE side of the rotor and leaving unpotted space between the magnets.  As the air is pumped outward between the magnets, some of it will be pulled through the holes to the other side.

Another might be to have one rotor larger than the other, and extend the magnets-as-pump-vanes with some non-magnetic material.  The side with the larger diameter "pump" will have a lower pressure, sucking air IN the other side, through the stator, and out the wide side.

ULR suggested not potting the ends of the coils at the outside where they are most likely to see some air flow and if you don't need the potting for weather protection this is likely to be the most effective.

Making holes in the magnet rotors in the correct place and not potting the magnets so that they act as fans seems very sensible and you will induce some radial air flow over the stator. If you don't need weather protection you could combine this with leaving the outer end loops unpotted and you could even spread the end turns a bit.

If you DO spread the turns to improve airflow, or even don't bind them together, you should pot or bind a short section in the middle of 'em.  They receive a varying "pinch" when the current flows.  If they're not somehow supported against it this will make them vibrate, flex, and fatigue at the point where they emerge from the potting.

By messing about with extra cooling you may be able to maintain power without furling to a slightly higher wind speed but as the power in the wind increases as the cube law you will only hold it off for a few mph. It may make the furling less critical with a bit more in hand for the winding temperature.

The AVAILABLE power in the wind goes up with the cube of wind speed.  But absent load effects the RPM and EMF (generated voltage before voltage drop from coil resistance) goes up with the wind speed.  If you were driving a resistive load the current and load torque would go up with the voltage and both power delivered and the resistive heating go up with roughly the square of the wind (a little faster because the load torque would be too low to keep the TSR down with increased wind).  If you had a max power point controller making the current and load go up to track the wind, the wind speed, RPM, and voltage would go up together, the current with the square, and the heating with the FOURTH POWER of the wind speed.  (This is why you MUST get your furling right or have a "max current" override in the controller if you do MPPT.)

For the usual rectifier/battery combo the current doesn't start until cutin RPM, then rises rapidly and linearly with RPM and voltage, putting a load on the blades that, if it weren't for wiring resistance, would stop the RPM from rising at all.  Since there is resistance, the current rises with RPM-above-cutin and the heating with the square of that, while the increasing current load causes the RPM to rise more slowly than the wind, and the blades to eventually stall out when the discrepancy becomes so great that the airflow detaches from the back side of the blade.  Obnoxious to try to compute this.

If you find a way to match the load then this issue mostly disappears and you can get 3 times more power out of the same stator without dropping below 60% efficiency and the heating problem is very much less.

In particular:

 - If your MPPT controller has a max-current-limit function, when the wind is high enough it can let the RPM and voltage climb, tracking "max power I can get without melting the coils" rather than "max power the blades can grab from the wind".  (This actually ignores a sliver more you could have grabbed, due to extra cooling from faster wind.  But let's not work too close to meltdown.)

 - If you use delta or IRP/Jerry-rig, you can get almost twice as much power out as Y for a given amount of stator heating.

[joestue]

- If you use delta or IRP/Jerry-rig, you can get almost twice as much power out as Y for a given amount of stator heating.

only if you specify a battery load.
a dc-dc converter to facilitate 'mppt' tracking wouldn't care if its delta or wye.
IRP is the least efficient, as it draws more harmonic current from the alternator than delta or wye.

[Ungrounded Lightning Rod]

- If you use delta or IRP/Jerry-rig, you can get almost twice as much power out as Y for a given amount of stator heating.

only if you specify a battery load.
a dc-dc converter to facilitate 'mppt' tracking wouldn't care if its delta or wye.
IRP is the least efficient, as it draws more harmonic current from the alternator than delta or wye.

Let me PARTIALLY back out of that statement.  The "almost 2x" is from the max power of the SAME PMA wired for Y vs. Delta, i.e. in a Y-Delta switch mill.  Part of the extra power comes from running delta at a higher RPM, achieving more volts-per-turn and thus more watts per current density.

But another part of the improvement is that Y runs all the current through two windings in series with the voltage out of phase and thus summing to under 2x, while delta runs 2/3s of it though only a single coil.  This ends up producing less resistive heating for a given amount of power and copper even if you're spinning the magnets at the same RPM and have either adjusted the turns ratio and wire size or have done a constant-power voltage-current swap with external equipment.

IRP/Jerry-rig runs all the current through only ONE coil or another, never through coils in series.  But the coil current waveforms are more uneven than those of Y and Delta, so the square law of resistive heating vs. current bites you harder.  This both reduces the advantage and makes the type of load more significant.

[Flux]

This just comes back to tracking the load.No single winding, star delta or anything else is going to make much difference as the load voltage is fixed but the alternator voltage needs to roughly track wind speed to work properly.

Any connection that changes the winding voltage will help, star delta or series parallel makes a big improvement near cut in and near full load the snag is that on most days the thing is mostly in the wrong mode and at the change over point neither is matched well. It is however much better than making no attempt. Where you set the change over point makes a big difference to how much you can increase the rating above that of a single winding.

As a mater of interest my findings on efficieny of the various schemes is that if you run with sensible loading star is most efficient, delta ia poor near cut in and has a lot of drag below cut in. Jerry( IRP) removes the drag below cut in and tends to be more efficient than delta over most of the range but these differences are relatively small and are not really relevent for a change over scheme, I still would avoid delta if possible for a single winding scheme as it hits the low power near cut in rather badly.  It is far easier to do a star/Jerry change than star/delta.

I suspect people will still chase the cooling ideas rather than look at load matching but in reality they are mostly chasing survival rather than really worrying about using the better cooling for capturing morre energy. You may well be able to double the current output with better cooling but you will need high winds to see the benefit. A decent load matching scheme gives 2 or 3 times more power with only slight increase in wind speed as the improvemrnt mostly comes from the prop and the ability to maintain the alternator efficiency high.

I agree that in the end the better matched scheme does mean that the furling HAS to work to protect in high wind whereas it probaqbly doesn't in stall regulated cases if the stall is hard enough to limit the power. The dangeruos case is direct connectrion where stall is hard enough to keep things under controll normally but the alternator is not stiff enough to prevent it pulling through stall under rogue conditions. if furling is not holding it at the point where it would pull through you have no certainly that it will come in in time for any protection once it breaks stall as you have never been in a position to prove it.

My thoughts on this are that big machines are probably safest run hard stalled but require large and expensive alternators. Smaller ones are better off with enough inherent rresiatance to run clear of hard stall, they give a lot more power and they have to furl so you can see whether it is working or not.

The cheapest way is to include the resuistance in the winding but you then need to concentrate of cooling or early furling, I prefer overbuilding the alternator for hard stall but adding line resistance that way you get the same result but have much less heating worries as the main loss is external and you may be able to use the heat for something useful.

I see it being worthwhile spending time and effort on cooling if it gets you more output in the wind speeds that you frequently get, if it is just to prevent burn out in storm from lack of design in other areas then it seems time and money wasted.

Flux

[Flux]

Sorry that slipped out before I checked it, the spelling and grammar is a bit off in places but I think it is intelligible.
Flux

[joestue]

- If you use delta or IRP/Jerry-rig, you can get almost twice as much power out as Y for a given amount of stator heating.

only if you specify a battery load.
a dc-dc converter to facilitate 'mppt' tracking wouldn't care if its delta or wye.
IRP is the least efficient, as it draws more harmonic current from the alternator than delta or wye.

Let me PARTIALLY back out of that statement.  The "almost 2x" is from the max power of the SAME PMA wired for Y vs. Delta, i.e. in a Y-Delta switch mill.  Part of the extra power comes from running delta at a higher RPM, achieving more volts-per-turn and thus more watts per current density.

But another part of the improvement is that Y runs all the current through two windings in series with the voltage out of phase and thus summing to under 2x, while delta runs 2/3s of it though only a single coil.  This ends up producing less resistive heating for a given amount of power and copper even if you're spinning the magnets at the same RPM and have either adjusted the turns ratio and wire size or have done a constant-power voltage-current swap with external equipment.

IRP/Jerry-rig runs all the current through only ONE coil or another, never through coils in series.  But the coil current waveforms are more uneven than those of Y and Delta, so the square law of resistive heating vs. current bites you harder.  This both reduces the advantage and makes the type of load more significant.

The only part that bites is the details!