Anotherpower.com Forum
Renewable Energy Questions/Discussion => Wind and Hydro => Topic started by: birdhouse on April 04, 2012, 03:09:08 am
-
saw this on youtube, seems a tight airgap would be tricky with all the overlapping wires!
http://www.youtube.com/watch?v=fF9zBkq5mAM&feature=related (http://www.youtube.com/watch?v=fF9zBkq5mAM&feature=related)
adam
-
Plus it will have a higher resistance.
G-
-
saw this on youtube, seems a tight airgap would be tricky with all the overlapping wires!
That's Sam Chamas up in Canada. I helped him build a couple generators better than two years ago and he's big into the serpentine windings, which require an elaborate winding jig but work quite well. Ed Lenz has used serpentine windings on his machined stator plates for years, with 1:3 pole/coil ratio and overlapped phase windings.
The serpentine winding eliminates the extra resistance associated with coils because you eliminate one winding head. So you can fit more copper in and get more volts out of a given diameter.
I got a half dozen serpentine wound stators laying around here. But I always had problems with harmonics in my high output generators and could never keep the stator tight. Now that I've gone to a different method of mounting my stators, I could use them. But they're still noisy running because they'll hit the first harmonic at a certain current frequency and the whole unit howls like a wolf on the hunt.
With Sam's slow speed generators he doesn't have that problem.
--
Chris
-
thanks for the explanation chris!
i'm continually amazed at how many different ways there are to build an alternator.
adam
-
I remember Tom and I think zubbly discussing this style of winding years back.
I am not sure but I think I remember that I used this for a gen I made with microwave mags.
Not so sure anymore I made a couple different stators for this and bench tested , before putting it up live and finding it has a major flaw in design. Eventually it became destin for the recycling heap.
-
For anybody that wants to learn how to build a serpentine wound three phase generator I can highly recommend Ed Lenz's little kit:
http://www.windstuffnow.com/main/3phase_turbine_kit.htm
It comes with the three coils already pre-wound, has one of his machined stator plates with it, has excellent instructions with it, and for only 42 bucks will show you how to build a serpentine wound 6 pole/18 coil generator the right way.
It's a little VAWT turbine that makes more power than them converted Delco 10SI "PMA's" that get pedaled on eBay all the time.
--
Chris
-
I had to turn off the porno soundtrack, other than that it's pretty cool, bout five minutes too long though.
-
with 1:3 pole/coil ratio and overlapped phase windings.
The serpentine winding eliminates the extra resistance associated with coils because you eliminate one winding head. So you can fit more copper in and get more volts out of a given diameter.
That video is 1:4.
1:4 is overly complex 1:2.
1:3 is better than 1:2.
I will stand by my statement that it has more resistance.
Draw a 12 pole with 40 turns per phase, then do the math.
"get more volts out of a given diameter"?
-
Birdhouse,
I can find no reason to go with that technique. It is difficult, and offers no positive attributes not already available with the standard 3:4 simple version.
I cant agree with Chris on "The serpentine winding eliminates the extra resistance associated with coils because you eliminate one winding head. So you can fit more copper in and get more volts out of a given diameter."
So we must be looking at the same thing and seeing different things. (if you shift the bottom winding head under the next coil, you end up with the same thing without the overlapping problems, which as you said will increase gap.... so more resistance ... or less copper in the same winding window.
I agree with Ghurds summation, and it is unlikely to do as well as the standard fare.
I wouldn't be keen to waste my wire on it for the main show, but for an experiment........ maybe.
...............oztules
-
Birdhouse,
I can find no reason to go with that technique. It is difficult, and offers no positive attributes not already available with the standard 3:4 simple version.
I cant agree with Chris on "The serpentine winding eliminates the extra resistance associated with coils because you eliminate one winding head. So you can fit more copper in and get more volts out of a given diameter."
So we must be looking at the same thing and seeing different things. (if you shift the bottom winding head under the next coil, you end up with the same thing without the overlapping problems, which as you said will increase gap.... so more resistance ... or less copper in the same winding window.
I agree with Ghurds summation, and it is unlikely to do as well as the standard fare.
I wouldn't be keen to waste my wire on it for the main show, but for an experiment........ maybe.
...............oztules
Oz, with the serpentine coils, would the total wire and therefore stator resistance, also be effected by coils spacing? I can see the point you have made by coil winding being tacked up under the next coil in a serpentine arrangement. Reminds me somewhat of a sine wave. If, from the zero voltage point of the first wave to the zero point after a full cycle, the two points were cut and folded around, there would be a completed path.
Thanks for that realization.
-
"Reminds me somewhat of a sine wave."...... the area under the sine wave is of interest as we fiddle the coils too.
Coil spacing will be dictated by the pole count and diameter... in either winding scheme. If we make the magnets lonely (big intermagnet spacing) then the coils will be too. If we keep both the magnet size and number and the coils size and number the SAME, the area under the sine wave should be the same regardless of the diameter we place them on.
Bigger diameter, bigger the emf spike, but skinnier wave form... etc. Same for either system.
It is the vector addition of each wire added to all the other wires in the same phase that gives us the emf. Each wire will have emf dictated by flux change in proportion to the "angle of attack" at all points along the wire/coil. Reminds me somewhat of a sine wave.
We don't even need a N and S pole. The full sine wave shape will come up with just N poles passing the coil..... eg positive sign as say N magnet pole approaches, and back to zero at top dead center, and changes to negative sign after the magnet passes TDC and the coil sees a basically receding field....... presto full sine wave from a single pole. In this instance the emf max is when the magnet is over either leg
If we do that on a single wire, not a coil, TDC is when the pole is directly over the top of the wire ( zero emf) and sine will change to negative from there.
When we use N and S alternately, we want the S pole over one leg, and the N pole over the other leg at the same time ( of the same coil).... we double the changing flux and double the emf at that rpm.
Thats why we do what we do (in standard axials), and so coil placement can have a great effect on as to what happens, and when it happens.
Did that help or hinder :o
.................oztules
-
I guess I'd have to refer back to my notes on the half dozen or so of those that I built. But I do believe that the resistance of them was 2-3% lower than the "standard" 4:3 ratio "flat" three phase in all the homebrew books. And I believe Ed Lenz will tell you the same thing - he got 2-3% better rpm/volt performance with the serpentine wound 1:3 ratio units he builds on his machined stator plates in the same diameter or space.
The thing is, you don't need many turns of wire with the 1:3 ratio. I know one of the 12 volt ones I built only has 7 turns of wire in each coil. A similar 4:3 "flat" three phase would've needed 33 turns for a 12 pole, and by the time you add all the coil interconnects in, the resistance is higher.
GM alternators are an example of radial serpentine wound 1:3 ratio stator cores, and those typically will have anywhere from 3-7 turns per coil in a 14 pole, depending on the voltage.
--
Chris
-
"Reminds me somewhat of a sine wave."...... the area under the sine wave is of interest as we fiddle the coils too.
Coil spacing will be dictated by the pole count and diameter... in either winding scheme. If we make the magnets lonely (big intermagnet spacing) then the coils will be too. If we keep both the magnet size and number and the coils size and number the SAME, the area under the sine wave should be the same regardless of the diameter we place them on.
Bigger diameter, bigger the emf spike, but skinnier wave form... etc. Same for either system.
It is the vector addition of each wire added to all the other wires in the same phase that gives us the emf. Each wire will have emf dictated by flux change in proportion to the "angle of attack" at all points along the wire/coil. Reminds me somewhat of a sine wave.
We don't even need a N and S pole. The full sine wave shape will come up with just N poles passing the coil..... eg positive sign as say N magnet pole approaches, and back to zero at top dead center, and changes to negative sign after the magnet passes TDC and the coil sees a basically receding field....... presto full sine wave from a single pole. In this instance the emf max is when the magnet is over either leg
If we do that on a single wire, not a coil, TDC is when the pole is directly over the top of the wire ( zero emf) and sine will change to negative from there.
When we use N and S alternately, we want the S pole over one leg, and the N pole over the other leg at the same time ( of the same coil).... we double the changing flux and double the emf at that rpm.
Thats why we do what we do (in standard axials), and so coil placement can have a great effect on as to what happens, and when it happens.
Did that help or hinder :o
.................oztules
Sorry Oz, I was using the sine wave as picture reference not as a product of either serpentine or traditionally wound round coils. Also, I was thinking that with the serpentine type wiring arrangement that the further the magnets were apart, the more wire would be required. Sorry for not explaining very well and I still may be to vague.
Oz, I do like your explanation. Very well put and I did learn something. Hats off to ya.
-
I guess I'd have to refer back to my notes on the half dozen or so of those that I built. But I do believe that the resistance of them was 2-3% lower than the "standard" 4:3 ratio "flat" three phase in all the homebrew books. And I believe Ed Lenz will tell you the same thing - he got 2-3% better rpm/volt performance with the serpentine wound 1:3 ratio units he builds on his machined stator plates in the same diameter or space.
The thing is, you don't need many turns of wire with the 1:3 ratio. I know one of the 12 volt ones I built only has 7 turns of wire in each coil. A similar 4:3 "flat" three phase would've needed 33 turns for a 12 pole, and by the time you add all the coil interconnects in, the resistance is higher.
GM alternators are an example of radial serpentine wound 1:3 ratio stator cores, and those typically will have anywhere from 3-7 turns per coil in a 14 pole, depending on the voltage.
--
Chris
Chris, I do apologize for not making my question very clear to Oz regarding the wiring of the two type of stators. However, I think you helped answer my question as well. Thanks
-
I was trying to absorb everything oz said as well, and it makes sense.
The way I've always viewed the serpentine winding is that when you look at it, it looks sort of like a sine wave in a circle. The peak and valleys of the winding each make a "coil" but it's not really a coil, as the whole winding is one big single phase coil with the same number of peaks and valleys as you have poles. You just put bends in the wires do they can cut lines of flux from many magnets at once.
It works the same as a bunch of individual coils wired series for a single phase, but basically one winding head on each "coil" is missing with the serpentine winding. The winding heads don't do anything except connect the legs together and add resistance to the winding with regular coils. The serpentine winding gets rid of one winding head on each "coil".
I suspect that's why the serpentine winding has been used for ages in automotive alternators with great success. They aren't that common in axials because of the difficulty of construction. But stacking three phases can still yield a stator under 1/2" thickness if you build a decent jig or use a machined stator plate like Ed Lenz does.
The problem I had with every one I built was vibration. The windings vibrated against each other something horrible and the generators made weird howling noises at certain rpm and current freq. I never did figure out what caused that. I flew one for awhile but the noise was so terrible my wife made me take it down. She said she wasn't listening to it anymore, and I either get it off the tower or she was going to take it off herself with a 12 gauge shotgun :o
--
Chris
-
Lets be clear about this. Magic is magnetic fields and electric fields and gravity fields...we dont know what they are .... at all..... but apart from that there is no magic. We do know all we need to know about their effects and behaviour.
To induce an emf into a wire, it needs to have to see a changing field, and ideally at right angles to the wire direction (angle of attack for want of a better phrase)
It does not matter what winding style you care to use, if you keep the flux density and rate of change the same in all cases.... then it follows that you MUST have the same turns number for the same emf at the same rpm... no magic can change that.... very simple.
So all the winding styles have to achieve that same thing. The difference between like serpentine and like flat coils in epoxy or resin can be small or considerable.... they are hand made, and usually to accommodate the practicalities of the stator size etc.
If you try to emulate the 4:3 with skein, then the end loops will push the resistance up for the same emf (huge end loops)....... so to get around this folks try the magnet next door , or every magnet or any combination they please, but in the end it is the number of wires getting cut at the same time in the same phase that will generate the result. (angle of attack assumed the same)
If winding with serpentine or wave, then the chances are high that the flux density will have to change to accommodate the crossing of wire in the gap. With steel core this counts for very little. The Alts for cars take advantage of this. Very thick wire, few turns, and the slot directs the field...and the field is is at the behest of the regulator so all problems are solved. Air gap machines don't have this luxury, so for skein, or serpentine or layered, these problems are far more important to overcome, as are the end loop radius.
Serpentine does not solve the end loops. For every 2 bundles of wire in the legs, there are 2 loops to support the current path. eg for 6 poles, a single layer skein will cover three poles. It will encompass 6 end loops for the three poles..... same as using three coils. same result.
If we then inter wind a longer skein to encompass the 6 poles in a single skein, we end up with 12 loop ends, and 6 poles covered.... same thing with flat coils ie 6 coils, and 12 end loops. Serpentine does not get rid of any end loops. It just saves some practical winding problems.
The only thing you can hope to change when using any wiring scheme is the resistance (for the same gap and magnets), but the emf induced in a single turn in like circumstances will be the same regardless.
If somehow you can pack thicker wire of the same turns.... then it is a win. I cant see overlapping doing this, but if you found a difference, then it will likely have to do with flux density being different, or the attack angles on the legs are different, because the same turns will yield the same emf............unless you use geometrically different shaped coils I guess. With iron core that is not possible to mess with, but with free hand air gap..... sky is the limit I suppose.
So if you see an appreciable difference in an experiment, and it does not match the theory, then wee need to look for why. We understand very very well how electrons are influenced by magnetic fields, and this is the basis for tv tubes, and an endless amount of electronics all the way to atomic accelerators.
We can calculate for the tiniest variations... we cannot break the rules. How we interpret the results of experiments needs to be done very carefully, mindful that the rules cant even be bent.... so look for the real reasons something may not follow the rules.
When it come to theories that are not based in true science, then it's just a theory anyway.... otherwise known as an opinion, and society seems to be in love with that "science" at the moment.
................oztules
-
Lets be clear about this. Magic is magnetic fields and electric fields and gravity fields...we dont know what they are .... at all..... but apart from that there is no magic. We do know all we need to know about their effects and behaviour.
To induce an emf into a wire, it needs to have to see a changing field, and ideally at right angles to the wire direction (angle of attack for want of a better phrase)
It does not matter what winding style you care to use, if you keep the flux density and rate of change the same in all cases.... then it follows that you MUST have the same turns number for the same emf at the same rpm... no magic can change that.... very simple.
So all the winding styles have to achieve that same thing. The difference between like serpentine and like flat coils in epoxy or resin can be small or considerable.... they are hand made, and usually to accommodate the practicalities of the stator size etc.
If you try to emulate the 4:3 with skein, then the end loops will push the resistance up for the same emf (huge end loops)....... so to get around this folks try the magnet next door , or every magnet or any combination they please, but in the end it is the number of wires getting cut at the same time in the same phase that will generate the result. (angle of attack assumed the same)
If winding with serpentine or wave, then the chances are high that the flux density will have to change to accommodate the crossing of wire in the gap. With steel core this counts for very little. The Alts for cars take advantage of this. Very thick wire, few turns, and the slot directs the field...and the field is is at the behest of the regulator so all problems are solved. Air gap machines don't have this luxury, so for skein, or serpentine or layered, these problems are far more important to overcome, as are the end loop radius.
Serpentine does not solve the end loops. For every 2 bundles of wire in the legs, there are 2 loops to support the current path. eg for 6 poles, a single layer skein will cover three poles. It will encompass 6 end loops for the three poles..... same as using three coils. same result.
If we then inter wind a longer skein to encompass the 6 poles in a single skein, we end up with 12 loop ends, and 6 poles covered.... same thing with flat coils ie 6 coils, and 12 end loops. Serpentine does not get rid of any end loops. It just saves some practical winding problems.
The only thing you can hope to change when using any wiring scheme is the resistance (for the same gap and magnets), but the emf induced in a single turn in like circumstances will be the same regardless.
If somehow you can pack thicker wire of the same turns.... then it is a win. I cant see overlapping doing this, but if you found a difference, then it will likely have to do with flux density being different, or the attack angles on the legs are different, because the same turns will yield the same emf............unless you use geometrically different shaped coils I guess. With iron core that is not possible to mess with, but with free hand air gap..... sky is the limit I suppose.
So if you see an appreciable difference in an experiment, and it does not match the theory, then wee need to look for why. We understand very very well how electrons are influenced by magnetic fields, and this is the basis for tv tubes, and an endless amount of electronics all the way to atomic accelerators.
We can calculate for the tiniest variations... we cannot break the rules. How we interpret the results of experiments needs to be done very carefully, mindful that the rules cant even be bent.... so look for the real reasons something may not follow the rules.
When it come to theories that are not based in true science, then it's just a theory anyway.... otherwise known as an opinion, and society seems to be in love with that "science" at the moment.
................oztules
Oz;
Well said.
I like the "magic" analysis best.
Tom
-
"all the way to atomic accelerators"
erm ...dont know about that bit ...
throws a dead dog into the well...
a serpentine winding maybe might save the bit of restisance with the wire that links the coils ...
coils and magnets ..... :)
-
When it come to theories that are not based in true science, then it's just a theory anyway.... otherwise known as an opinion, and society seems to be in love with that "science" at the moment.
oz - do you have any theory why the serpentine stators I built vibrated so bad? I tried several different combinations - a couple 12 pole units, one 14 pole and one 10 pole, IIRC. They all did the same thing. It would hit a certain rpm where something matched between the current frequency and harmonics in the windings and the generator would emit the most terrible howl you've ever heard. It sounded almost like a bearing locking up. Get the generator running faster than that, or slower, and it would go away.
The one 10 footer I built and flew for awhile did it right about 200-250 watts, which is were it ran most of the time.
--
Chris
-
Niall..
"all the way to atomic accelerators"
erm ...dont know about that bit ..."
Did you read reactor rather than accelerator perhaps?
I think reactors use the weak force, rather then the electromagnetic force.... but...
The whole point of a particle accelerator/ atom smasher... is to use magnetic fields to both contain and accelerate charged particles.
.... and this is where the real magic is.
Consider electron behaviour in the super conductors for the electromagnets to keep the particles where you want them... and then why the superconductivity fails at 10^5 amps/cm^2.... weird magic to me.
Chris,
It is the back MMF working against the magnets that make the impulse. If your units made noise at certain speeds, it will be the natural resonance of the head and tower being lit up at certain frequencies.
Interestingly, the MMF reaction increases with current, but your noise decreased after a certain speed..... so it really seems like simple resonance of the system..... which unfortunately matched the normal running speeds. Single and three phase will behave differently, but at the right frequency, will still resonate . I expect single phase more so than three phase, as all coils get hit at the same time with the same reactive force, three phase spreads the pain a bit better.
..............oztules