20 Pole / 3-phase Alternator efficiency testing
By CmeBREW, Section Wind Posted on Sat Dec 8th, 2007 at 12:04:53 AM MST
20 Pole / 3-phase Alternator  testing

Greetings all.         I thought I would give some info and pictures on my first 3-phase alternator, and show some of the basic "efficiency" testing I have done with it--and since I am still learning the basic principles, ask a few questions to help me decide what I might do with this high voltage (120vdc) alternator I made.  The alternator is 3-phase 20 pole (20 mags each rotor) / 15 coils (5 coils per phase). The mags are only 1" diameter by 1/4" thick N42s.  Here is the layout board and a simulated plexy glass rotor I made to make sure everything is correct-- and everything checks out correctly.       The coils are 20ga. wire / 80 turns each. Wired in STAR. Unfortunetly, I did not bring out the other 3 wires at the end of the phases for more hook-up options. I thought I would not ever need them anyway. I was wrong. Originally, I made this alternator to be a VAWT.  So I purposely made the 'cut-in' voltage way down to only 70 rpm. I can see now that this alternator will NOT work for a slow rpm Vawt (direct drive/no gearing), because it severely STALLS when hooked to a 12v battery. I now know that I have NO IDEA how to make an efficient, easy to turn, slow rpm 12 volt alternator for a VAWT!! (I WISH I knew how) At one time I had thought I was out of STALL, but now I am certain it was still IN severe STALL. It is hard to tell since the PVC Vawt rotor(s) spin such a SLOW rpm. After recently testing this alternator with my 'triple gear reduced' 3.5 amp/ 600rpm sears drill, I can actually SEE, FEEL, and HEAR (the drill)  how much in STALL it really was, when hooked to the 12volt battery. So therefore, now I am wanting to use this alternator for a much faster rpm HAWT.  There is MUCH I have yet to learn about alternator EFFICIENCY. It is not so simple since there are SO many different aspects having to do with it. Here is some of the basic testing I did with my slow 600rpm (probably slower) 3.5 amp 'triple gear reduced' Sears drill. The plywood on top of the alternator is only so I could hook up my drill  with a bolt in the middle to go into the drill chuck for testing. In the photo, the alternator is DIRECTLY hooked (no batteries) to two 75 watt light bulbs. Before hooking to the bulbs, the OPEN VOLTAGE of the alternator being spun full trottle by the 550-600rpm drill, is 120vdc. (after the rectifiers) So with the drill going full throttle speed, the two bulbs light up and the ammeter says 1 amp. I believe that is about 120 watts.  The drill does not 'bear down' almost any when doing this. This next photo shows the 3  12volt batteries I tested the alternator with. The light is not hooked up. I simply tested amps going into the batteries with my ammeter. First I tested the alternator and drill with only the one 12volt battery , and then I tested with the 24 volts (2 batts in series), and then I tested with 3  batteries in series. (36volts) Previously, before doing any of these tests, I had opened up the mag air gap an 1/8" inch extra, for a total mag to mag gap of a 1/2". So even with this bigger air gap, and the alternater Hooked to the 12 volt battery alone, the drill could barely even turn the alternator! It started really bearing down on the gears of the drill at only 1 amp (12 watts) and for just a moment I was barely able to reach 2 amps max (24 watts) and the gears of the drill were ready to break. It could only turn the alternator upto about a very brief 120rpm. This was very surprising to me. I then hooked up to 2  12volt batteries (24 volts) , and now the alternator and drill was able to spin up faster (probably around 450rpm) and put 130 watts (5 amps& 26v) into the batteries. Quite an improvement I must say! (but the drill was bearing down quite a bit doing so) I then hooked up to 3 12 volt batteries (36 volts), and was able to get 180 watts into the batteries, but it was ALOT EASIER on the drill as it was able to go the full rpm of the drill without much bearing down on the gears of the drill. (probably around 550 rpm)  So if I wanted to close the mag air gap back at this point, I could have got alot more watts than just 180 watts. (probably around 240 watts) I thought all of this was very interesting testing.  It shows how important it is to have the alternator in the right "efficiency range" of one's battery bank voltage. I had known this before. However, I did not know that it would be THAT difficult to turn the alternator simply because it is so far out of the correct 'efficiency range' for a given battery bank voltage.  Why is it so hard to turn when hooked to the 12volt battery??  Does resistance have something to do with it? However, I still believe this would make a decent alternator for a 48 volt battery system. (I did not have a forth 12v battery for testing at 48volts) It would probably STALL for a 24volt batt system. Or , I was thinking that I could close the mag gap back, and allow it to be a 120volt alternator, and get a Dc to DC converter if they aren't too expensive.  Right now, my battery bank system is 12 volts. I can also make it 24 volts though. However, going to a 48volt system would be sort of difficult now. My C-60 charge controller (which is new and still in the box) only goes up to a 24 volt system. I would need to trade it for a C-40 which goes upto 48 volt battery system. I could always re-make the stator for 12/24 volts.  Or, I was thinking about 'digging out' the other 3 wires from my stator using my dremel tool so that I could do a 'Jerry connection' with a rectifier on each phase. I believe that might bring it down possibly into the 12volt range. If not, certainly the 24volt range. At least my first 3-phase alternator actually works!!  Its just WAY out of range. I was thinking about a 6 foot diameter pvc set of blades. Sorry for the long posting--- But there's ALOT to these alternators. Any thoughts, comments , or questions would be greatly appreciated!!!! Quotes removed from title because punctuation in titles prevents replies. [50 word limit bug] TW

20 Pole / 3-phase Alternator efficiency testing | 17 comments (17 topical, 0 editorial)

Re: 20 Pole / 3-phase Alternator efficiency test (3.00 / 0) (#1) by methanolcat (methanolcat (at)yahoo(dot)com) on Fri Dec 7th, 2007 at 07:51:38 PM MST (User Info)

Very nice looking stator, maybe you can grind away some of the resin allowing you to tap a single wire into the internal star connection then parallel all 3 phases and rectify them that way, if I'm thinking correctly that would cut your voltage by around half, maybe more.      Although separating the connection and adding 3 more wires would give more options as well but will probably be more difficult, but not impossible. Maybe use some pliers to break out small bits of resin.   Matt

Re: 20 Pole / 3-phase Alternator efficiency test (3.00 / 0) (#2) by wooferhound (tim((NoSpamAt))wooferhound.com) on Sat Dec 8th, 2007 at 01:52:38 AM MST (User Info) http://wooferhound.com

Paralleling all 3 phases before the rectifier will cancel the voltage out to zero W o o f -={( [ Parent ]

Re: 20 Pole / 3-phase Alternator efficiency test (3.00 / 0) (#6) by methanolcat (methanolcat (at)yahoo(dot)com) on Sat Dec 8th, 2007 at 06:28:12 AM MST (User Info)

Thanks Woof, I guess I didn't know that, you learn something new every day.         Matt [ Parent ]

Re: 20 Pole 3-phase Alternator efficien... (3.00 / 0) (#3) by fcfcfc on Sat Dec 8th, 2007 at 01:54:00 AM MST (User Info)

Hi: I am confused. If your VAWT is a drag type device, you cannot stall it and if that is the bottom of the VAWT in the one photo, I think it is way to small for that size gen.. On testing the gen with an electric drill, I think you are misinterpreting the way the drill is acting. First, when connecting to batteries there should be no load on the gen until it is spinning fast enough to reach the voltage of the battery. Once you attain that, the gen should start to load. So by going from a battery of 12VDC to 24VDC you are increasing the speed before you hit any load. Electric drills, especially variable speed ones, develop more torque the faster they spin. So I believe you are interpreting the low speed of the gen and drill strain at low voltages to be a gen problem when it is a input power problem. What you need is a power drive system that uses a heavily geared down motor so a huge amount of torque is developed. Another wards, power to turn the gen is a non issue. Then you can measure your output volts and amps at different speeds and get a true picture of the gen.. Input power is important for calculating gen efficiency, but that is somewhat of a separate issue from volts and amps at different speeds. In short, I think your gen is fine and I would not do any digging in the stator. You just need to match the gen to the right size VAWT on the "power in" side and use the right charging electronics on the "out side". My opinion... .....Bill

Re: 20 Pole 3-phase Alternator efficien... (3.00 / 0) (#10) by CmeBREW (smke833f@hotmail.com) on Sat Dec 8th, 2007 at 04:39:41 PM MST (User Info)

Hi Bill, thanks for responding.      I think you are right. Thanks for bringing that to my attention.(again) I believe now, that my understanding of the term "Stall" in somewhat off. Right when I thought I finally understood something!!. Go figure. My understanding of that term was (and still is) incomplete. I studied on it some more today from just a few things Flux and Dan have said on it recently, and it looks like the term "Stall" is used ONLY IN REFERENCE TO THE BLADES ALONE. (the angle of attack and TSR, and the way the wind flows around the airfoil on the back side of the blades in different wind speeds-- in relationship to the alternator's resistance and the alternator holding back the blades) So if the alternator literally is HOLDING BACK the blades somehow, it changes the way the air flows around the blades, reducing 'lift' to the point of "Stall". Is that correct?? I was previously thinking that since Hawt blades are FIXED at there given angle (4 or 5 degrees at the tip), that the term "Stall" was mostly meaningless in reference to the blades, since no one here actually has a windmill with a Variable pitch Hub.(or;variable pitching blades)  I knew that "Stall" is usually used in reference to an airplane's wing 'angle of attack' becoming TOO steep (tilted up beyond 12 degrees) and the plane loses most or all 'lift' and drops like a rock.   I was thinking that everyone here was using the term "Stall" to mean that the COILS IN THE ALTERNATOR are HOLDING BACK the blades from turning upto an optimal speed, and thus, "stalling them" much like a car trying to take off in 3rd or 4th gear. I can see that that is only part of it, but not nearly the WHOLE story. When I used the term STALL in my posting in reference to the VAWT, I was simply meaning that the alternator (stator coils) was HOLDING BACK the Vawt rotor from spinning faster because the coils were evidently so mis-matched to the battery voltage. I will not use the term like that no more. It is even more complex than I had thought. I'm sorry for the confusion. I will keep studying on it. I still believe the testing I did with the batteries was interesting. THe drill I used is a High torque triple gear reduced low rpm drill. I see what you are saying about inertia increasing with rpm, but I don't think it played THAT big of a part in this particular testing. I use this drill to make upto 2" diam holes thru floor truses and 4x4's going very slow rpm (100 rpm or so) and it does it fine with alot of torque. Your right about the cut-in voltage. It was 80rpm with 12 volts, about 160rpm with 24 volts, and about 240rpm at 36 volts. I forgot to mention that in the post. I still think making and matching an alternator to its best, most efficient system voltage range is smart to do. I now want to make a HAWT mill with this alternator, since winter is here now and the sun is going away.  I am going to try something different with the Vawt though. I'm going to try to gear a treadmill motor to it. At least I know how to do that! -Thanks. [ Parent ]

Re: 20 Pole 3-phase Alternator efficien... (3.00 / 0) (#13) by fcfcfc on Sat Dec 8th, 2007 at 09:35:24 PM MST (User Info)

Hi: Thanks for the reply... Without commenting on all the comments, its not that the drill gets momentium as such, its the actual power changes as the speed increases. When a motor has voltage applied to it, for the first split second there is a huge current applied (drawn) because the motor is not moving. This is what is called the starting amps of the motor. The reason this happens is that the motor is generating no back EMF which opposes the incoming EMF reducing the current drawn. As the motor spinns faster and faster the back EMF keeps increasing until the motor reaches is peak run speed and stable no load current draw. As you apply load to a motor you slow it down which reduces the back EMF causing more current to be drawn and stronger fields to be generated. The "strain" you hear is more a function of the current drawn than anything else as well as the heat generated from it. Remember there is no magic here. The alternator can only load up in as much as there is load put on it. Drawing 12 watts (1 battery test)and hearing your drill "kill itself" and then your drill doing pretty well on the three battery test (36VDC) but producing much more output power, MUST not be taken to mean that it actually was taking more power to turn the gen when it was producing the 12 watts than it took to produce the larger number of watts at the higher speed. You might actually get a better feel for the gen at low rpm's and loads if you put some kind of hand crank on it. You could probably do 30 or so rpm yourself and really "feel" the power needed at different loads... and you are right, stall is strictly an aerodynamic term applying to lift designs and has nothing to do with motors of gens... Just my thoughts.. Good luck on what ever you decide for your unit.... [ Parent ]

Re: 20 Pole / 3-phase Alternator efficiency test (3.00 / 0) (#4) by tecker on Sat Dec 8th, 2007 at 04:39:30 AM MST (User Info)

I have the feeling you don't want to cut into the stator just yet ( white paint and all) so . To use the high resistance stator you'll need  series resistance to keep up with the current lag of each phase . My personal Choice is a water heater I 've scrounged two (I had one and acquired one) .I use a tankless on inverter as the wind is not happening when I want to shower so the two other 30 gal are good preheaters . With awg 20 your good for 10 amps per phase (Phases separated and parallel into a common dc load I think is your best idea)without cooking the the plastic Possible around 25 to 30 amps max  . Your Vawt has to get bigger Taller , wider or both .Both require top bearings if you break down the rotor and get bigger and wider and go to an H frame .  I'm pretty sure you can get the drag you need with your design at 3 times the diameter and a three section modified s  rotor in the middle to block and use the wind through the center .Your blades have to be turned more tangent to the circular plane to lift the on coming air instead of scooping it and pushing it out . That should work

Re: 20 Pole / 3-phase Alternator efficiency test (3.00 / 0) (#5) by tecker on Sat Dec 8th, 2007 at 06:24:45 AM MST (User Info)

I just recieved these and found they are a good fit to 1/2 " copper I don't have one now but I think a 1/2" couplin is a prefect fit .6.8 ohm 200watt  Good series resitance and that much series resistance doesn't effect charging . [ Parent ]

Re: 20 Pole / 3-phase Alternator efficiency test (3.00 / 0) (#7) by electrondady1 on Sat Dec 8th, 2007 at 09:00:18 AM MST (User Info)

cmebrew , i hope you don't abandon your vawt as you have built a real beauty and i think it has great potential. i am interpreting your use of the term "stall" as meaning a reduction in rpm due to the load the alt creates once it reaches cut in speed. i think you are in a situation were you need to out torque your alternator. if i recall correctly you mill has a wept area of about 10 sq. ft. that's not much in comparison to the needs of your alt. you have already proven that the design of your mill is robust enough to withstand strong winds with out an exterior support structure . i recommend you increase the height of your support post by the length of your mill or more . mount the alternator as you have previously at the top of your "tower" construct a duplicate mill with appropriately sized support rings.   mount it so that it fits over and  will sit  below the alternator and encompass the support post . now mount your existing mill on top as you have been doing. you have now doubled the swept area. with out adding any support structure and in fact have balanced the horizontal moment on your mill. i would avoid increasing the dia. of your mill as that will reduce its rpm and and make your alternator less productive . if you can cut into the stator and get at the star point. it gives you some options. http://www.otherpower.com/images/scimages/2793/little_erma_004.avi [ Parent ]

Re: 20 Pole / 3-phase Alternator efficiency test (3.00 / 0) (#8) by electrondady1 on Sat Dec 8th, 2007 at 09:26:10 AM MST (User Info)

ok, that worked !! it's a different configuration, but i think you can see what i mean about balancing the load on your bearings. i built "little erma " before i got a computer and discovered "other power" the alternator is wacky  as all i had to go on at the time  was a grade nine science book. one thing i have discovered here is that for a drag vawt swept area is everything. good luck on your experiments and keep us informed. [ Parent ]

Re: 20 Pole / 3-phase Alternator efficiency test (3.00 / 0) (#12) by CmeBREW (smke833f@hotmail.com) on Sat Dec 8th, 2007 at 06:37:09 PM MST (User Info)

Thanks Electrondady,         No, I am not abandoning my Vawt projects by any means. They're always interesting to me. Its just that winter is here now and the sun is completely leaving, and so I now am wanting to make a 5 or 6 foot diameter HAWT (NORMAL,horizontal windmill) out this alternator and keep it fairly low to the ground (10'pole) and risk it all from being shut down by the local government. Whatever happens, happens.  (I've had my small 4' mill up for a year now) But I will keep doing Vawt experiments though. I have several tests planned right now. I don't mean to change the subject from my altenator problems, but heres a  picture of what I have been doing most recently with one of my vawt pvc rotors. The diameter is 18 inched for more rpm and the height is almost 5 feet for more torque. I changed the angle of the blades 4 times and now the blade angle almost points straight in toward the center point. It is much more aggresive this way. More speed and alittle more torque, but it is much more UNSTABLE now. It does not self-stabilize anymore. It starts swaying so bad I have to short the alternator and stop it. So therefore, I am going to put a steel centering/stabilizing bar straight up the middle of the rotor to FORCE it to remain stable in bigger winds. I will weld the bar to a steel disc and bolt it down to the hub bolts in the middle.   And I'm going to test it with 24 volts instead of only 12v. I've never done that before. (among many other tests with resistance in line) I also am going to try and GEAR a treadmill motor to this vawt rotor and see how it does. (4:1 /or 5:1) So I have plenty of fun experiments planned --even though it is freezing now outside. Thanks for the ideas. Nice Emma Vawt by the way.         [ Parent ]

Re: 20 Pole / 3-phase Alternator efficiency test (3.00 / 0) (#11) by CmeBREW (smke833f@hotmail.com) on Sat Dec 8th, 2007 at 05:38:45 PM MST (User Info)

Thanks Tecker.          I did some experiments today with putting various resistance in the line (hooked to only one 12v batt), but the outcome was not that good. I did manage to make some nice little 'heaters' though. But only 40 watts or so was going into the battery after these two 1 ohm heating elements.(Also the drill was bearing down very hard and could only turn about 200 rpm or so) I put a higher resistance element (the heating element from a 120vac/1500watt space heater)in series in the line (hooked to just one 12v batt again), and the drill WAS very easy to spin up to maximum speed, BUT, it only allowed 2 meazly amps (26 watts) to go into the battery.  I quess somewhere in the middle then would work better.   I need to keep studying on this subject and doing more testing to understand it better.   [ Parent ]

Re: 20 Pole / 3-phase Alternator efficiency test (3.00 / 0) (#15) by tecker on Sun Dec 9th, 2007 at 02:51:16 AM MST (User Info)

With the heating elements in series you see what you have at your disposal starrred three phase into a 12 volt battery ,Impeadance unknown . Lets say the marine Batt at 12.25 . The  resistance allows the turbine to stay spinning with what will be the best you can do into a 12 volt battery load . You want the higher voltage for the trip from the mast to the charging station that's good . You don't need the increase star connection offers to work your load . You need to rethink the starred stator and breakit up to your likeing . These are good tests and now  you have realtime data to form a turbine with . Maybe (like you said )cut into the star node and bring out three more wires to run to the charger .  Drag Vawts are in the 50 to 200 rpm range Lift Vawts 100 to 300 and able to speed up fast in wind gusts . Hawts could use the starred stator but you risk burnout. Amps from the drill would be a good bit of data. [ Parent ]

Re: 20 Pole / 3-phase Alternator efficiency test (3.00 / 0) (#9) by wooferhound (tim((NoSpamAt))wooferhound.com) on Sat Dec 8th, 2007 at 03:24:50 PM MST (User Info) http://wooferhound.com

Maybe it's possible to Gear it Down it's a different direction in gearing than we usually think of W o o f -={(

Re: 20 Pole / 3-phase Alternator efficiency test (3.00 / 0) (#14) by Flux on Sun Dec 9th, 2007 at 02:16:01 AM MST (User Info)

Your tests with the drill and series resistors are not going anywhere. Adding series resistance will lower the battery charging efficiency, that is inevitable. Adding resistors gains you extra power from a wind machine by bringing the blades out of stall. Although you lower the electrical efficiency you more than make up for it by raising the blade efficiency. When you try with a drill, the drill motor doesn't produce more power to compensate. From your figures it seems as though your 12v cut in is around 60 rpm. Far too low to be much use for a 6ft HAWT. If you insist on trying pvc blades then I suggest you try 3 or 5 blades and see how it works at 24v. For decent wooden blades it looks as though you would suit 48v. At 120 rpm cut in into 24v with a slow prop you may get reasonable results. If it fails to increase power with wind speed then is the time to try adding those line resistors. If you can get a reasonable match to a 6ft prop, the power from that in a good wind will be much more than your drill so things may look somewhat better. If all else fails break into the star point bring out 3 more leads and Jerry connect. Good luck Flux [ Parent ]

Re: 20 Pole / 3-phase Alternator testing (3.00 / 0) (#16) by CmeBREW (smke833f@hotmail.com) on Sun Dec 9th, 2007 at 12:30:35 PM MST (User Info)

Thanks Flux.   I understand what you said.  I was thinking of using 6 pvc Hawt blades for the high turbulance area this mill is to be placed. PVC blades are very easy to make. I will try this first with the 24volt system. If need be, I will use the resister in series to loosen it up a bit, as you said. If all that fails, I will most likely try the stator 'surgery' with my dremel tool. This does physically weaken the stator alot though. After I perform this 'surgery', I was wondering if anyone here has ever tried to pour Epoxy back over the hole and wire connections to make the stator strong again. INotherwords, does anyone know if Epoxy will adhere well to Fiberglass polyester?? I know super-glue melds into the polyester nice, but I've never tried epoxy.  No matter WHAT happens , I can easily re-make the stator, since I have plenty of extra 16ga and 20 ga wire, and the wood mold I used is still in perfect shape. So its no big catastrophe anyway.    -Thanks.

Re: 20 Pole / 3-phase Alternator testing (3.00 / 0) (#17) by DanB (danb@*no spam*otherpower.com) on Fri Dec 14th, 2007 at 07:49:07 AM MST (User Info) http://www.otherpower.com/

Epoxy will setup/adhere fine on cured polyester resin, however polyester resin will not usually setup well on epoxy. [ Parent ]

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