question about coil resistance

[devoncloud]

OK, so now that windstuffnow has us understanding his way of winding his staters with multiple layers of coils, I do have some questions still.

1. It seems that Ed keeps the number of winds on his coils very low.  I am sure this has something to do with space and resistance, but I still have some questions that maybe the group can answer for me.

a.  It seems the more layers of coils you have (such as three seperate phases in star in ed's last generator)the more rectifying you need to do.  I am wondering which is better:  Making a bunch of smaller coils (even if this means four or five single phases as long as there is room on the stator) or if three single phases with more wire would be the way to go.  It seems on one hand, if you make four or five single phases with a small amount of turns per coil, you have much less loss due to resistance since the electricity has to travel alot less distance before it reaches your rectifiers per coil.  While you gain power output due to less resistance, you will still need more rectifiers which gives you some losses anyway.  If you stick to three single phases and add more turns per coil, then you add resistance and heat since you increase the distance the electricity has to travel before reaching the rectifier (causing more power loss)but save some loss due to less rectifiers.  Am I right in this thought or would you have the same amount of resistance/heat anyway because the same amount of wire is still in the stator, but just seperated into more coils?

b.  If I am right which one would be more beneficial: three single phases with less rectifiers or four or five single phases with more rectifiers?

2.  Kind of off the topic of number one, but one thing I have been trying to figure out for the longest time is how I can make a generator with basically two stators:  The first one would produce alot less power output but would have a great start up speed, and the second stator would have great power output but not a great start up speed.  I have come up with two ideas that might work, but I would like your input

a.  The first idea that I had was to make one or two of the "single phases" as described above much smaller wire size to decrease startup speed.  The only problem with that is when rpm's increase enough to make the larger wire sizes produce, the small wires will of course overheat.  Is there a way to "turn off" these smaller wires after the rpm's kick up enough to have the larger wires produce?

b.  My other idea (which I may look into a little more seriously) would be to make a  generator using a 12" magnet rotor.  I would use larger magnets on the outer edge of the rotor while putting smaller magnets twards the inner part of the rotor.  I would make two different stators in essence but the smaller one would fit in the center hole of the larger one:  One bigger stator that would go around the larger magnets and of course would be wound with larger wire, and a smaller stator that would go around the smaller magnets which would be wound  with smaller wire to gain a better start up speed.  Of course the smaller stator would fit inside the middle of the larger stator, so there would be no increase in air gap.

Does anyone know if either of these is workable?

Devon  

   

[BT Humble]

2.  Kind of off the topic of number one, but one thing I have been trying to figure out for the longest time is how I can make a generator with basically two stators:  The first one would produce alot less power output but would have a great start up speed, and the second stator would have great power output but not a great start up speed.  I have come up with two ideas that might work, but I would like your input

The stator on Hugh's current dual-rotor design is basically 5 independent pairs of coils[1].  If you want to start generating power at very low windspeeds without sacrificing too much high-speed performance, why not wind one (or possibly two?) pairs of coils with more turns of a smaller diameter wire?

So far as I know that's how it's done with the commercial Air 403/X turbines, and it shouldn't make any difference to the balance of the machine?

BTH

[1] Please feel free to correct me if I'm wrong here!

[devoncloud]

The problem I see is that the smaller wire will burn up if you try to maximise the output of the larger wire at the same time.  I think the air-x and those other commercial units have a way of shutting the smaller sizes off or run something similar to my other suggestion (b), but I'm not sure.  I would like to be able to maximise the output of the larger wire while taking advantage of a slow start up speed as well, and by simply making one of the phases in hugh's design a smaller guage wire than the other phases, I do not think that would do it.  I may be wrong though, I am pretty new at this stuff.

Devon  

[windstuffnow]

  Devon,

     One of the reasons I can use less turns is because there are more coils.  Another reason is because the single phase configuration allows the magnets to do more work which in turn creates higher voltage/current.

     The dual rotor I reciently built is wired in star, just like a normal 3 phase machine which means you can use regular rectifiers.  I use the type that are in automotive alternators, specifically the ones in the 10si Delco's.  You do, however, have the option to split them into 3 single phase units and rectify them individually and either parallel them or series them for different outputs which makes this design quite versitile as far as the possible outputs ( i.e. star - delta - single phase parallel or series ).

     I believe I posted some time back about the possibility of making a "progressive" alternator as you suggested.  Using one phase with lots of turns for low wind, the next phase with medium wire for mid range and heavy wire with low turns for higher winds.  You would most likely have to have a way of shutting down the low wind coils at a certain point or they wouldn't last very long. A relay powered by the high end coils may allow you to shut down the low wind coils. This arrangement would require separate rectifiers.  It would be an interesting project and a good challenge getting them all to interact properly with the prop.

     Infinate possibilities !!! Have Fun

Windstuff Ed

[devoncloud]

thanks for the info ed.  But, I am still wondering... You say that the reason you get away from using more turns is because of the number of coils.  Is the amount of resistance lessened since the current has less distance to travel to the rectifier (less amount of turns = less resistance)or does it not matter since you are putting the same amount of wire in the stator after it is all said and done?  In other words, it would seem you are creating less heat per coil which is allowing you to push the system harder to create more output by using 36 smaller coils than if you were just to make twelve coils with alot of windings.  Because you are generating less heat per coil, you are transfering much more energy into electricity than you would otherwise since you are not loosing so much energy due to heat.  Is this true?  If it is true, would 48 coils work better if you could fit them in there?

Devon

[devoncloud]

ok, upon second thought, I wish to change my theory on the resistance.  I guess that you would still be comming out with the same resistance but not the same heat.  Say that you have twelve coils that equal 2000 turns of wire and 36 coils that equal 2000 turns of wire, and you put them under the same load under the same exact conditions.  Lets say that the twelve coil stator was running at 300 degrees per coil.

The 36 coil stator would only run at 100 degrees per coil, right?  

[windstuffnow]

  Using this wiring scheem I've found I can cut the normal amount of turns ( total turns ) by half and still get the voltage I need at a given rpm.  This also cuts the resistance by 1/2 ( give or take ).  

  I'm not sure going with more phases per say would add any more power since there is only a certain amount of space on the stator and 3 can fill it up quite well.  If, however, you added more magnets, thus more coils the amount of turns would be decreased once again and the spacing between the coils becomes smaller.  For instance the same alternator as my last one with 14 poles and 14 coils per phase would only need 7 turns per coil.  The coils become smaller and require less footage.  So instead of 76.8 ft per phase mine has now it would require only 54.7 ft per phase or reduce the resistance to .35 ohms per phase or .7 in star.  Increasing it once again to 16 poles ( you start running out of space ) and 16 coils per phase you would only need 5 turns per coil and thus drop the footage once again to 42 ft of wire reducing the resistance once again to .27 or .54 in star.  Unfortunately the 16 on an 8" disc won't work without causing alot of canceling because the coils are very close together.  With 12 you have a spacing of 10 deg apart with 14 its spaced 8.57 deg apart and with 16 its 7.5 deg apart.  At that point you'd have to go with a larger diameter and start over.

    Anyway thats how it works out, less is more

Have fun

Windstuff Ed

[stop4stuff]

2a... yes you can turn off the small coils, with a switch to open the circuit. With no current across the coil it won't burn up. The switching system would have to know when to switch over tho.

[Victor]

Hi Devon,

  I think the Air 403  used three different windings with thermistats on the two smaller gage wires to keep them from burning up. The themistats were in series  with the wire and apparantly are heated by the current going though them and open when hot. The Air X is very different and electronically adjusts the output to windspeed.

Victor

[stop4stuff]

like the bimetallic unit in an auto indicator (flasher) relay?

[hvirtane]

I think that a dual coils system

arrangement with the thinner wire coils

switched off at higher RPMs might

be one working solution.

Another solution?

We used with my friend Taisto Suihkonen

a transformer to get the voltage rapidly

up to be able to charge batteries with

low RPM. The alternator is connected

parallel with the transformer to another

rectifier, which is connected to

the battery, too. When the voltage is

high up so that it can go the battery

directly bypassing the transformer,

the most of the electric current is doing so.

The advantage of this method seems to be

that you can use less turns with thicker

wires in the alternator so that it will

not become hot with higher RPMs.

A disadvantage is the need to use a

transformer with a little losses

and some added cost and complexity.

You also need two rectifiers...

- Hannu

[systemtwo]

"The first idea that I had was to make one or two of the "single phases" as described above much smaller wire size to decrease startup speed.  The only problem with that is when rpm's increase enough to make the larger wire sizes produce, the small wires will of course overheat.  Is there a way to "turn off" these smaller wires after the rpm's kick up enough to have the larger wires produce"

Devon

you could try using the centrifugal switch out of a cap start ac motor you will have to play with the spring tension

David

[mayfair]

I've considered the question about low wind startup and high wind efficiency.

The losses in the windings are I^2 * R, so if I is minimized, the efficiency will be maximized.

To minimize I, run at a high voltage output (100V or higher) and use a buck-type switching converter (after rectification and filtering) to deliver the voltage to the batteries.  At 100V, 10A=1 kW and 50A=5 kW.  Using polyimide (220 deg celsius) rated [magnet] wire, 50A could easily be run with 10 AWG windings.

If the switching converter is operated with an appropriatelly programmed microcontroller sensing input voltage and current at the converter input, maximum power could be extracted from the wind generator in any wind condition, as the generator would see its optimum load at all times.  This is identical to maximum power point tracking for solar arrays (e.g. Solar Boost(tm).)  The 100V at 10A (for example) would result in ~14V at 64A into the batteries (with 100W dissipated in the converter, assuming 90% converter efficiency.)  That same microcontroller could also switch the output (or input) to a diversion load when the batteries were full.  

It could also have a charging algorithm for the batteries (bulk, absorption, float [and equalize if required] with output voltage sensing.)  Since it would know the input power and converter efficiency, it would know the output current given the output voltage.  In this case the diversion load handling must be thought out carefully, and the system load current monitored.  Probably switching a diversion load onto the battery bank would be the best way to control the battery charging in this case (and a second converter could be used to vary the diversion load too.)