coils ?

[ubud]

Coils ?

I've been researching all of the proven designs as to number of turns per coil, and am trying to figure out feet per coil.

Why you ask?

I have 44# of 21 guage magnet wire,(bought it on EBAY For $2.09 per lb.) ALL ON 1 LARGE SPOOL, and am looking to multiple strand coils, ie. 21 ga. x 10=8100cm or about 11 ga wire (BY my old ARRL HAND BOOK WIRE CHART)

From the Master, (I think I'LL Call him SIR HUGH PIGGOT), all of his designs come out at aprox. 120' (12 V)

From the Dan's (Many Thanks for a LOT OF VERY GOOD INFO) Very close to aprox. 120' (12 v)

From ED @ WIMDSTUFFNOW, 10 t 12 slots Aprox 120' (12 v)

As I look at ALL the coils they all seam to come out around 120' total wire length, and start to charge at about 150 rpm 13.8 +.7v (for blocking diode) = 14.7v

Can I then assume .1225 volts per foot, at cut in rpm?

My frist PMA, 12 pole  9 coil star conn. gives me cut in at about 155 rpm (40 ft of 1 16 ga and 2 strand 24 ga Total 3391 cm.)

3 coils series, 3 phase. not in the air yet.

I hope to get it right the first time, cause I'm gonna have to cut and spool for 9 coils.

Any help/ comments will be appreacated.

Frank

[wooferhound]

On my turbine there are 2 sets of 3 coils at 125 turns per coil

one set of 3 coils gives me about 12 volts at 250 rpm t

so that is 3 coils times 125 turns equals 375 turns 12 volts at 250 RPM

In your question you do not say anything about how many coils are in series for each of these machines or phases, nor do you state the RPMs ?

This would be helpful to answer your question

A simple answer would be

Turns equals voltage

Feet equals resistance

So the resistance of more feet will decrease the voltage made by the number of turns

or

More turns will make more voltage that will be decreased by the resistance of the feet

[richhagen]

I got confused a bit on what you were saying above, but basically:

If you are building a 3 phase machine and are using 3 coils in series for each phase, then make one test coil with a known number of turns equal to a guess of what you think you will need, and measure the no-load voltages of that one coil.  

To measure that voltage, stick the test coil in what will be the approximate final air gap between the two magnet rotors.  Then spin up the rotor to a known rpm and record the voltage.  The voltage obtained from the final coils will be proportionate to the number of turns in the coil, and proportionate to the number of rpm.  

Because of this we then have all of the information we need to design our coils.  For each phase the coils are connected in series and placed such that the magnetic flux across each coil is the same at any instant in time, the output voltage is the sum of the AC voltage from each coil (when doing your final assembly make sure you have them connected correctly so that the voltages add).  Then the open circuit voltage of the wind turbine in AC can be calculated.  If you connect the phases in STAR configuration this would be the voltage from one phase (3 coils in series) multiplied by the square root of 3.  For Delta, the calculation of the final output would be just the voltage of one phase.

Thus if you know the rpm and voltage output of your test coil, you can figure out how many windings per coil are required to reach your desired cutin speed. The output of your alternator is AC, and then you rectify it through diodes to DC.  if the battery voltage is around 12.6, you will actually start pushing a little current into them when the AC voltage is about 9.7 volts, as the peaks of your sine waves will be the square root of two times that voltage and then take off the 1.2 volts or so lost in rectification and you have your 12.6 volts.  That being said, traditionally, the cut in speed is taken to be when the AC voltage reaches a higher value at 12.6 volts AC (for a 12V battery) from the alternator from most of the stuff I've read as the alternator doesn't generally push much current, or slow the rotor appreciably below about that voltage anyway.  

Now you can calculate the number of wires required for each coil.  You can select the largest guage of wire (or wires if connecting several in parallel) that you can fit in the space available for each coil between your rotors.

Once assembled, you can adjust the airgap a little bit to increase or decrease the rpm required to start charging you battery as well if you don't peg it to your target exactly.  When the alternator starts to charge, depending upon the resistance in the line to your battery bank, the rotor will become resistant to increasing speed as the wind increases, which can lead to a condition where the prop spins up and then if the winds aren't sufficient stalls out, then the cycle repeats.  Increasing the air gap, or the resistance in the leads to the battery bank can correct that problem should it arise.  

I don't know if this answers your question, and I'm sure others will have more to add, and may be better at explaining the phenomenon, but I hope that this helps you some.

Rich Hagen

[FrankG]

Rick,

I've been watching this thread in hopes that it would answer a question that I've been thinking about as well...

I'm at a similar point as "UBUD" in that I have some materials finalized, in his case the wire is not a variable as he just purchased a large spool of it. While in my case I have a good supply of Hard Disk magnets. As well I have numerous 6 1/2" Circular saw blades... I can appreciate that designing around materials on-hand generally leads to a series of comprimises that degrade the final product, but can act as an instument of education in that you really have to understand the properties of the components to get the most out of them.

The link below is to a diagram that I fiddled about with between Xmas Dinner and the traditional cards games and family stuff yesterday...

http://www.theworkshop.ca/energy/hdgen/magtemp.jpg

Assuming that the link above displays, my objective is to wire the 8 coils in series for a 12V charging system... I realize the 3 phase is more efficient, but want to get this under my belt first and learn as much from the series configuration as possible.

Your point about the AC voltage yielding a "Higher" DC voltage has me confused... @ 9.7VAC times 2 and then Sqrt gives me ~4.4V... So this will only hold true for 3 Phase in "Star" to sum the 3 legs???

In my case, size of the wire and the # of turns per coil is still variable. My objective is to determine the optimal number of coils, size and gauge to get 13V plus DC given the restraints of using HD mags mounted on a 6.5" rotor with a modest output of 9 to 10Amp (totalling approx 100Watts). I have determined that stacking the magnets does in fact bump the output voltage (and can play with that factor). Also I have read enough accounts that I trust that a permeable metal backing on the magnets does also offer greater flux out he faces of the magnets (my justification to move to the saw blades over the wooden backing I orginally tried per...

http://www.theworkshop.ca/energy/hdgen/hdgen.htm

Given that I go with the 8 coils as laid and I try a variety of windings to predictably achieve a specific AC voltage per coil... the sum of each coil should be cumulative and add up to a summed AC output. What should I be aiming towards on a per coil basis, and what is the basic calculation to determine the rectified DC output?

Thanks in advance for any replies...

[richhagen]

Hi, It looks like you have a good source of magnets there!  First off, The alternator will put out three phase AC current if wired that way.  If you wire yours for single phase and then rectify it, the peak DC current will be the equivelant of the peaks of the wave form coming out from the rectifiers.  These peaks are equal to the square root of 2 (1.414 approximately) times the root mean square of the AC voltage, which is the AC voltage measured with an rms meter.  Those peaks reach 12.6V coming out of the rectifier when the AC rms voltage reaches about 9.75 volts.  The peaks are at about 13.8Volts minus about the 1.2 volts you lose as heat in the rectifier.  I might be incorrect on the three phase above as in thinking about it, the voltage across the rectifier is the voltage between two legs which are out of phase, and I was thinking in single phase.  I'll have to give that some more thought.

I've never tried to build an alternator with so many magnets per coil like your diagram, however, keep in mind that the direction of the wires is reversed in each leg of the coil, so if you are changing the flux in the same direction at the same instant, the voltage and current induced will be in the same direction in each leg.  I believe you will cancel out the voltage and warm your coils.  I believe that you would want the leading leg of the coil to be in a condition where the field is changing from say north pole to south pole when the trailing leg is switching from south pole to north pole, that way the induced currents are in opposite direcions and pushing the current around the coil.  Based on the size of your coils relative to the two pole magnets I think that will be a problem.

In general 3 phase will be more efficient and will run more smoothly because the drag on the mill will be more evenly distributed in time than in single phase.  That being said, single phase does work as I have built alternators that way.  Rich Hagen

[wooferhound]

I am looking at your diagram and it looks incorrect. Every coil has both legs over the same poles of the magnets. Half the coils are over 2 norths and half the magnets are over 2 souths. Coils should end up having one side of the circle (Leg) over a north and the other side over a south in order to get the maximum voltage.

It looks like you could get 12 coils in there and generate a LOT more power. Plus the resistancee will be lower because the coils will be narrower making less wire in the areas that are not over the path of the magnets.

[FrankG]

Rich,

I think I get it...

I started to read through my dusty old text books from the last century and see where the 1.414 comes from... On a pure sine wave the RMS value is calculated at 0.707 which is 1/sqrt of 2.

I did set-up a disk with the 24 poles as in the diagram, and wound a few more coils to see what the effect would be... a 200 turn awg#24 was hitting 1.2V to 1.3VAC with no core consistently. The DC resistance reads 1.0 ohms, Though I assume that the "impeadance" of the coil would vary with the frequency of the sine wave generated (since no one is getting into that end of it I may be just looking for trouble, and will just let it lay)

Given 8 coils X 1.2 = 9.6VAC (RMS), X 1.414 = 13.6 less the diode loss of 1.2V and I'm right in the zone!!!

When I set up the coils into a stator, I'll leave the pig-tails towards the outside and wire them one at a time to ensure that the phase is cumulative...

I think one of the other issues that has been tripping me up is that I keep thinking that I'm looking at 12 magnet, though in fact it is 24 (given the 2 poles per face).

Thanks

[FrankG]

Woof,

My logic in sizing the coils per the diagram was that one of the consistent features I've seen in all the diagrams posted has been that the open center of the coil should straddle an entire pole.

The testing I did last night was with a 0.75" dia winding bobbin and the coil thickness was close to 0.5" on either side of the bobbin (close to the image above). It did read 1.2 to 1.3VAC (RMS) per my meter (as I'd noted to Rich)... Though what I'd not mentioned was that I'd tried a variety of larger & smaller coil sizes in an effort to meet the criteria that you mention, having a "Leg - leading or trailing edge of coil" over an opposing pole. and the voltage readings seemed to drop off on either side of the 0.75" coil dia.

I know that this flys in the face of numerous other posts, and it makes me question my own findings... One of the differences I can see is that typically others have used disc mags and spaced them with a distance that is close to the dia of the disc. While I have opted to cram the dual poled HD mags Pole to Pole with little to no gap.

In an effort to clarify this, I still have the wound coils, I'll layout the 12 pole equivelant (breaking the magnets & leaving a blank space) to see if there is an increase, decrease or no change in the output.

I can appreciate that more magnets is not neccesarily more power as there has to be a point where the fields do cancel themselves out. Of note though is that when I was using the "Magnet-Pan" for sifting the "Black-Sand" I did notice that the flux density is very high arround the outer most edges of the individual poles. While a small amount of black sand would accumulate in the very center of a pole. See diagram per link below...

http://www.theworkshop.ca/energy/hdgen/polequestion.jpg

If this is possible than yet another assumption is shotdown in flames (that HD Mags have only 2 poles per face, while in fact they have a total of 4)... I think that this may just be complicating things...

[monte350c]

Hi Frank,

I believe Woof is right about this. Having the same pole over both legs - cancellation.

If you leave your current geometry the same and turn every other magnet 180 degrees it should work out. (NN SS NN SS etc)

But you will have some fun persuading the two magnets to stay together ie N to N.

Ted.