Author Topic: Box Fan Motor Conversion  (Read 12995 times)

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johnlm

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Box Fan Motor Conversion
« on: February 09, 2006, 09:59:11 PM »
This write up is primarily designed to be a tutorial for beginners to small shaded pole motor conversion.  The conversions shown in this tutorial are not pretty and polished looking by any means as most of these are pretty much the results of repeated experiments with winding and rewinding, glueing on, removing and reglueing magnets many times to improve cogging or output capabilty. Most of the glue jobs are done with super glue and hot melt for a less than permanant unit in case additional modification is needed.  Hopefully a few techniques or bits of insight may provide for the new experimenter to be more sucessfull in their own box fan motor conversions.


Although I had experimented with the conversion of a shaded pole 20 inch box fan motor back a couple of years ago, I became more intrigued when about a year or so ago there were discussions in a post where several folks talked about a possible contest to try to get 10 W at 10 mph for under $10 out of one of these motors.  The one I had previously converted was good for around 15 Watts at 1000 RPM using the stock windings and ceramic magnets (Lowes 1-7/8 X 7/8 X 3/8 cut in half); however I presumed that one could do better.  So I took the motor out of an old 20 in fan (vintage about 1965) that I had inherited from my parents and started experimenting.

Using the same 1/2 Lowes magnets and stock windings of about 1200 total turns of stock AWG 24 windings, once again I got about 15  W at 1000 RPM.  I was able to get about 22 volts AC (31 V DC) out of the conversion at 1000 RPM, which seemed reasonably suited for a 3 ft prop but the most significant shortcoming to use it for 12 V charging was the relatively high DC resistance and high inductance of the windings (13.5 Ohm dc resistance and a total of about 24 Ohms ac impedence @ 1000 RPM)  This meant that for every amp of current I tried to draw from it, the voltage drop inside the windings would be about 24 Vac, resulting in nothing on the output. In other words the shorted out current capability was only about 0.9 amps. I experimented with dividing the 1200 turns contained in the 6 poles (200 turns per pole) into two sets of 3 poles in series working in parallel with the other 3 poles.  This obviously cut the output voltage in half but resulted in the output impedence being reduced by a factor of 4X.  So now I had a unit that at 1000 RPM would put out 11 VAC (15.5 V DC) and had an output impedance of around 6 ohms.  Much improved except the output RPM / DC Volt rating was around 64.5 RPM/V and cutin for a 12V battery (13.4V charging) would be almost 865 RPM which is pretty high for 3 ft prop if I wanted the cutin wind speed to be around 6 to 7 mph.  A much smaller prop than 3 ft diameter (or high TSR) would have difficulty starting one of these conversions in less than a 8 to 10 mph wind.  So I decided to cut out the old windings and rewind it with a larger diameter wire, and also try using some small 1 X 1/2 X 1/8 inch neos I had bought from Windstuff Ed.  The following pics and words will help explain how I did that and add insight into some of the above.





This (above) shows the final product of the box fan motor converted with new stator windings, a new longer shaft, 6 magnet poles using 2 each of the neos per pole (single phase operation).





Although this is not the armature in the white fan motor conversion, it is an original armature out of one of these box fan motors.  Had I decided to use the thin 1/8 inch thick neos in the white motor to start with, I might have just tried grinding down 6 flat areas, corresponding to the 6 stator poles, on the original rotor to mount the magnets; but since I started out using much thicker 3/8 in thick Lowes ceramics cut in 2 pieces I did not want to do that much grinding, so I came up with the idea to build a new rotor using the original shaft with the rotor pressed off.  I looked around and found some pipe that was the correct size such that once the 3/8 thick magnets were mounted to it, they would fit with a small amount of clearance inside the stator.  I then cut out disks from OSB board (chip board, although plywood works well also) that would fit inside the pipe, and bore out a 1/2 inch diameter  center hole to re-insert and super glue the original shaft. I later built a new rotor from a larger diameter piece of pipe that I used to mount the neos.  The following pics show various stages of this new rotor assembly.





The disks  are cut out with a drill type hole saw.  If there is a gap between the outside diameter of the disks and the id of the pipe, I usually wrap masking or duct tape around the wooden disks to make for a snug fit, then squirt in some super glue to glue it all together.








Above is an assembly with 8 neos for use in a 3 phase (8 magnet, 6 stator pole) unit.





Above shows various pieces of pipe, conduit, etc for use in various assemblies.





This is a rotor (minus the shaft) using the Lowes 1/2 ceramic magnets that I initially used in the white fan conversion.





Above is the rotor assembly presently used in the white fan conversion.  I initially tried using 6 neos but they were not too much better than the ceramic magnets and because they were so narrow relative to the face of the stator poles the was alot of cogging.  So I mounted 2 each side by side X 6 sets to line up with the 6 stator faces.  NN - SS - NN - SS - NN - SS  The magnets are somewhat skewed to reduce cogging.  Surprisingly this rotor only presents about 1.5 ft ounce of cogging torque but the gap between the magnet faces to the stator pole faces is about 3 to 4 millimeters.  If the gap were closer I think the cogging might be worse.


Now comes the stator modifications.  Most of these small shaded pole motors come with multiple windings using anywhere from AWG 24 to AWG 27 wire.  The more speeds the fan has the more complex the wireing arrangement.  One can try to determine the number of turns, DC resistance, wire guage etc to try to find a useful combination of parallelling windings, or poles etc to get some useful results, and I have done this on several units, but all in all, if the original windings are not larger diameter than AWG 24 wire, it is easier to just remove the original windings and rewind it with the appropriate number of turns of a wire size that meets your design needs.  One way to try to determine the number of original turns if you have already built a rotor assembly to make the original stator at least work as an alternator is to wrap maybe 25 separate new turns of say AWG 24 wire around one of the stator poles and bring those leads out through the case and crank up the alternator with a drill or lathe or whatever at some known RPM and take a reading of the AC voltage to come up with an RPM per Volt number so that you can determine how many turns you might need altogether on a rewound stator.  Or compare the output voltage of the newly added windings to the output voltage you get off one of the original windings and find the ratio.  For example, if you are getting 2 volts out of the 25 new added turns and you get 30 V out of one of the original windings you know you have an output of 25 turns per 2 volts or 12.5 turns per volt on the new windings X 30 volts on the original winding gives 375 turns on the original winding or 62.5 turns on each of the 6 poles.  





The above pic shows a closeup of the shunt found on each pole in these shaded pole motors.  This is what gives these types of AC motors the ability to start since they do not have a separate start winding.  This is just a heavy copper band that effectively shorts out part of the pole region.  I usually try to remove these shunts especially if I take out the original windings.  If you are going to use the original windings you might cause more damage to the windings trying to removethe shunts than what it is worth.  Ive measured - although not very precisely - the effects of having them in verses removed and I think the performance is better with them removed; however leaving the shunts in is not a real show stopper.





Above is the white fan motor stator rewound with AWG 18 (1 MM diameter) wire.  I was able to get 100 turns on each pole, and as you can see its not wound the neatest job in the world. The white gue is hotmelt glue just to keep the winding from shifting around.  When I finally get the units done where I care not to do any more modifications I usually coat the stator coils with a couple of heavy coats of spar urathane varnish to set them in place.   When rewinding these stators you must be sure that the cardboard / phenolic / painted on insulator material that sits down in the cavity is intact.  If not the new windings will get the enamel insulation damaged as it bends around the corners of the laminates, and it will short out the windings to the laminates.  There is nothing worse than spending a couple of hours tediously winding several hundred turns of wire on a stator only to find the wire is shorted to the metal laminates.  In this particular motor it used a heavy cardboard as the insulators (typical of a 40 year old motor) on the laminates and I damaged them significantly tearing out the original windings (they were a bit brittle from age I think) so I reinsulated the cavitys using several alternating layers of masking and scotch tape.  It probably wasn't the best thing to use but as I said in the beginning I was just trying to get something built to experiment with - to see if I could get more power out of one of these units.  When rewinding you also have to be careful not to nick the enamel insulation as you pass the wire through the narrow slot between the poles.  On one unit the gap was so narrow that I took a file and filed off a millimeter or so on each of the sides of the T tops on the laminates to get more space to easily run the wire through, and then added a layer of scotch tape on the ends of the T s to buffer the wire from being scratch by the raw laminate metal.


Once you determine how many turns of wire you think you need to get the output you want at a give RPM, you can estimate how many feet it will take by estimating the average diameter and calculating the length for each turn. (assume a more or less round winding around the pole stump)  Don't just measure around the pole stump and assume that as the final size as the diameter will increase as the turns build up.  Then pick a wire size that will enable you to get that many turns on.  I really see no need to use larger than AWG 18 wire in these little motors, and probably the best size to use is AWG 20. If you are going to need alot of turns because you want to generate fairly high voltages for say 24 or 48 V use you may want to use no larger than AWG 22 or 24.  And if your wanting higher voltages than that you may as well keep the original windings and add more turns on top of them and connect the end of the original winding to the start of the added windings to put them in series to get the higher voltage.  I have found that I can get in the neighborhood of 0.005 Volts AC per turn per 100 rpm with the 1/2 Lowes ceramic magnets (single phase) and about 0.0083 Volts AC per turn per 100 RPM with the two neos on each of the 6 poles (single phase).  These numbers vary somewhat (+/- 30 %) depending on the spacing of the magnets from the stator pole faces and what size the stator is and several other variables but it gives you an idea of what to expect.





The white fan alternator ready for the front cover to be put on.





This is a pic of a slightly larger (1/12 horsepower) shaded pole motor that I converted using the full size of the Lowes magnets, since the stator thickness was about 1.25 inches thick, I use the full magnets to get coverage over the entire thickness.  On this unit it was already wound with 60 turns of awg 20 on each of the 6 poles, so I added 30 additional turns per pole of AWG 20 for a total of 540 turns to get the output to what I wanted.  I kept the tap where I joined the new windings to the original and brought it out so I have a unit that will put out at around 30 RPM/V dc (original winding) or 20 RPM/V dc both winding in series, or 60 RPM/V dc new winding only.


The white fan alternator with the 12 neos has the following specs:



  1. neos 2 each on 6 poles
  2. turns total (100/stator pole) AWG 18 wire.
  3. V DC output at 310 RPM


DC resistance of windings: 1.4 Ohms

Ac output impedance at 60 Hz (1200 RPM): 5 Ohms

Power capability into a 13.3 V Battery at 1000 RPM 5.1 Amps (68 Watts)


When driven by a 4.15 ft diameter 3 blade prop, (TSR=4.4 approx)

Cutin slightly over 6 mph

@ 10 MPH windspeed 1.6 Amp into the Battery

@ 15 MPH 4.2 Amps into the battery.


Johnlm

« Last Edit: February 09, 2006, 09:59:11 PM by (unknown) »

ghurd

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Re: Box Fan Motor Conversion
« Reply #1 on: February 09, 2006, 03:32:58 PM »
Excellent!

The genie, the numbers, and the post!

There is so little good information for the smaller stuff.


Something like Rich said, `If it works- it's not ugly'.  I agree.


Is the 4.15' at 4.4TSR prop about right?


I am very glad to see I am not the only one using hot glue. At least sometimes.

G-

« Last Edit: February 09, 2006, 03:32:58 PM by ghurd »
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zap

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Re: Box Fan Motor Conversion
« Reply #2 on: February 09, 2006, 04:02:09 PM »
Very nice Johnlm, I just started a box fan conversion today following ghurd's article here and having your's helps.


I had a little trouble following your wiring stuff ghurd but I'm still going at it. Thanks to both of you!

« Last Edit: February 09, 2006, 04:02:09 PM by zap »

johnlm

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Re: Box Fan Motor Conversion
« Reply #3 on: February 09, 2006, 06:26:46 PM »
Ghurd,


I agree, there is not nearly as much written about small to medium sized mills.  There was quite a bit more a year or so ago but lately the push has been for bigger and more powerful, which is probably appropriate since most people want to produce enough power to be usefull for household purposes.  I like playing around some of this smaller stuff because you can get results fast and if you need to change things its easy, and its cheap.  As I said in another post a couple of days ago, and forgot to state in my write up I have about $20 in this white fan motor conversion and most of that is for the 12 small neos at about $1 each.  The larger unit pictured at the end of the write up has about $15 in it.  $5.00 for the motor from a used tool and hardware store nearby, $8 for Lowes magnets and about 1 to 2 $ for added wire.


Ive converted, including rewinding 4 car alternators, 4 or 5 shaded pole fan motors, a couple of small PC cooling fan motors, and a few other things, ranging in wattage from around 200W capability on the Delco car alternators to a couple of watts on the pc fans.


This white fan motor works well to keep the RV battery on my camp trailer up in the mountains charged up between my weekend stayovers.


You asked: Is the 4.15' at 4.4TSR prop about right?

I think probably anything from a 3.5 ft to a 4.5 ft prop on this alternator would work ok.  It kind of depends on where you want cutin and what kind of wind speeds you want to do most of the charging in.  If you live in a pretty windy area maybe a 3 ft unit would do ok and get the alternator started with a 7 or 8 mph wind.  At my spot in the mountains the typical (non summer storm times) windspeed when it is blowing along the ridgline is up to about 12 to 15 mph tops so I went with a bit larger prop that is large enough to get started at around 5 mph with a TSR that runs the alternator fast enough to maximize its output.  The prop is typically running up in the tsr range of 6 to 8 above 9 or 10 mph windspeed even though its loaded design TSR is around 4 to 4.5 as it has enough power to not get pulled down to the design TSR.  I have the head set to begin furling around 15 to 17 mph since Im not always around to try to shut it down when a summer thunderstorm rips through with 25 to 35 mph gusts.  Ive seen it handle those speeds, but if you don't need the power of 35 mph wind gusts why let it rip and tear on the mill.


Im going to have to try your 4 magnet 6 pole approach using these neo's.  Since Its a piece of cake to pull the magnets off these pipe section rotor plates and remount them I can probably change one over in 5 minutes.  On some of these conversions cogging has been an issue especially trying to get the alternator to start in low winds with a small prop.


Johnlm

« Last Edit: February 09, 2006, 06:26:46 PM by johnlm »

ghurd

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Re: Box Fan Motor Conversion
« Reply #4 on: February 10, 2006, 06:56:13 AM »
For mine, there were 3 seperate wires on each coil. I connected them end to end, so when its done, it is one LONG wire made of 3 pieces. Clear as mud?

G-
« Last Edit: February 10, 2006, 06:56:13 AM by ghurd »
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zap

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Re: Box Fan Motor Conversion
« Reply #5 on: February 10, 2006, 10:09:58 AM »
Maybe not mud... still muddy LOL

I cut all three wires on each side of every coil then tied all three wires together so I had 6 separate coils basically wired 3 in hand. These were then connected to it's opposite coil. We'll see, still need to grind down the rotor but that's an outside job and we got some snow.

« Last Edit: February 10, 2006, 10:09:58 AM by zap »

johnlm

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Re: Box Fan Motor Conversion
« Reply #6 on: February 10, 2006, 11:31:00 AM »
Zap,

As I mentioned in the write up, but did not expound upon, the problem with just identifying the 3 separate windings and then connecting them in in parallel - which is what it sounds like you did- is that often the three different windings have different numbers of turns.  When connected in parallel you have one winding trying to generate one voltage and another winding trying to generate a different voltage.  The net result is that the two windings (or even all three) are fighting each other and desipating power inside the windings.  The only redeeming factor in all this is that the wire sizes used are small enough that the resistance (and impedance) is fairly high so the power being burned up inside the windings is usually not enough to cause any damage.  The same problem is mentioned at times in posts on this board with 3 phase alternators wired in a Delta configuration.  If the number of turns and the actual resistance (due to slightly more wire in one phase than another) are not the same then the same kind of fighting effect happens resulting in excess heat being generated in the windings.


This is the reason I spent some time talking about trying to find out the number of turns in all the different windings if you were going to try to use the original coils and tie them in parallel.  Tieing them in series as Ghurd mentioned above does not create any problem other than makeing for a really high  output resistance and impedance which will limit the current capability, but have the upside of having a much higher output voltage. The high output voltage feature could be useable if you wanted to use a relatively slow speed prop such as the fan bladed that came on the box fan or lawn ornament type windmill blades. Trying to determine the number of windings gets a bit tricky especially if the different windings are different guage wire as I have seen more often than not in these motors.  However; having cautioned you on all this, if all you want to do is just get a unit working and you are not worried about getting higher effeciency or achieving any certain output capability then doing what you did will work. It would be interesting to see what you come up with, including pics.  As I said before and as Ghurd says, its a small group of us that seems to have fun screwing around with this small stuff, mostly just for the fun of it.  There have been some folks talk about making small windmills similar to ornamental lawn windmills except with more effecient props, and these cheap box fan motors (1 to 2$ at garage sales) are the cats meow for doing that sort of thing and maybe even being able to get 10 or 20 watts of power which is more than enough to charge batteries for sidewalk lighting, small christmas displays, or what have you.

Have fun

John

« Last Edit: February 10, 2006, 11:31:00 AM by johnlm »

zap

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Re: Box Fan Motor Conversion
« Reply #7 on: February 10, 2006, 02:39:09 PM »
John thanks so much, that cleared everything right up. I felt that's what ghurd was trying to say in his original post but reading it, looking at his drawings, then re-reading started my synapses firing in all directions and I was soon more confused than when I'd started.

I'll post some pics if it ever comes to be, I've got some hd mags that fit the armature to a tee(sic)so I'm thinking it shouldn't be too tough.
« Last Edit: February 10, 2006, 02:39:09 PM by zap »

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Horrific cogging
« Reply #8 on: February 15, 2006, 11:25:01 AM »
I got my armature cut, ground, and filed down and got my magnets cut and temporarily glued down and had pretty bad cogging. Also the output voltage wasn't great but the cogging needs remedied before working on the voltage. Here's a shot of one of the old 5.25" HD magnets cut in half (cut side to side, the cut side is along the bottom, hidden from view) and stuck to a stator pole.



I noticed that ghurd's magnets covered maybe half of the stator pole, mine cover just about all of my stator pole and when on the armature there's about 1/16" air gap, give or take. The magnets were skewed a bit from sloppy workmanship but it was still cogging like a... ahhh... well it was bad.


To cut down on the cogging I come up with these solutions, shown in the order I believe would be easiest to hardest. I guess skewing the magnets might be the easiest but I could probably only skew them so they were in an "X" shape more than a "+" shape when viewed from above, would this take care of some of the cogging?



  1. - (this one is just a guess on reducing cogging...will it work?)cut the stator poles down, i.e. cut some of the fins off of each end of every pole.
  2. - cut the magnets down more but which way? Lengthways... so they're not as long as the stator, spanwise... so they're not as tall as the stator (right now they're about the same hight)
  3. - increase airgap by grinding down the armature more.


So do any of these sound best or is there some other way? Help me boys!
« Last Edit: February 15, 2006, 11:25:01 AM by zap »

ghurd

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Re: Horrific cogging
« Reply #9 on: February 15, 2006, 08:53:37 PM »
The magnets I used were only because they were already here and they fit. Don't read a lot into it.


Does it have 6 magnets?  Then cogging is going to be a problem. No matter what.


New idea. Never tried it. And I'm tired. Sort of short out the cogging.

With 6 magnets, move them closer together in neighboring pairs, with more space between pairs of neighbors.  N-S--N-S--N-S.


Not sure about the magnets. Are they neos?  I was told neos will saturate the laminations even at a distance, meaning open the air gap (grind the armature more). The power shouldn't go down a lot, but the cogging will. Don't over do it.


Cutting the magnets down more doesn't seem like a good idea to me. They don't look like neos, so you want all you can get.


Don't cut the fins! The cogging will get worse.


It looks like there will be problems the way it is wired. Some coils will back feed the others.  If the explaination John gave is to complex, at least seperate the green wire and put it in series with the other 2 in parallel.  "I think" the green wire is going to suck up all the power, backwards, from the other 2, and that opens up a whole 'nother can of worms.


Again, don't cut the fins.

G-

« Last Edit: February 15, 2006, 08:53:37 PM by ghurd »
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zap

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Re: Horrific cogging
« Reply #10 on: February 15, 2006, 10:21:50 PM »
Only 4 mags, I was trying to follow your post from July.


Pretty sure they're neos, super strong, out of old 5.25" scsi HDs. Look about like the one's wondermagnet used to carry that were surplus.


Roger on the cutting the fins, maybe for a quick try I'll split the magnets in half from top to bottom. I have some more drives so getting a few more magnets would be easier than more(ugh!)filing on that armature.


As for the wiring I think I did it like you did, at least in your picture from the July post.

I cut all three wires between each coil then hooked up it's opposite coil on the other side in series so they were both wound in the same direction. Like I said, I'm not real concerned yet about the wiring, I'll worry about that if and when I can rid this thing of it's cogging. Here's a pic of the stator but I doubt you can see how I've hooked it all up so here's a stupid drawing also. Hard to tell but basically I end up with 3 sets of 2 coils each wired 3 in hand... at least that's what I figure it is.





Thanks for the help G... I'll keep posting progress.

« Last Edit: February 15, 2006, 10:21:50 PM by zap »

ghurd

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Re: Horrific cogging
« Reply #11 on: February 15, 2006, 11:57:22 PM »
I wrote a lot of confusing stuff. Then I cut it.


I have no idea what the wiring diagram (statorwiring) means.

The 3 phases do not appear to have an output.


The photo (statomagratio2) is a lot different than the wiring I tried to show.

Mostly the end of copper wire #1, goes to the start of green wire, end of green wire goes to start of copper wire #2. The start of copper wire #1 and the end of copper wire #2 are outputs.

The end of 1A is connected to the start of 1B, etc.


That leaves 3 pairs of outputs. Those are wired in 3 phase for rectification to DC power.


I would be glad to sort it all out in your comcast email if you respond.


It is just a minor wiring problem.

G-

« Last Edit: February 15, 2006, 11:57:22 PM by ghurd »
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johnlm

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Re: Box Fan Motor Conversion
« Reply #12 on: February 20, 2006, 08:23:01 AM »
As I said befor on the wireing, unless you really know how many turns of each of the windings you have, you are shooting blind trying to determine what to do with them.  As suggested if you want to use all the original windings you can connect them all in series and get a fairly high output voltage at alower RPM at the cost of high resistance, but you do get something.  One other way to get an idea of the ratio of turns on the different windings, now that you have the rotor working somewhat is to independently measure the ac output voltage on each set of windings while turning the rotor at a given rpm.  Hook it up to a 1/2 inch drill or something to run it at several hundred (or whateve the drill runs at) rpm and measure each winding.  If two of the windings put out the same voltage then they likely have the same number of turns, and could be tied in parallel.  If they are all different output voltages, you cannot determine the exact number of turns but you can calculate the ratio of turns to each of the other windings.  on most of these conversions I try to get the AC output voltage in the neighborhood of 18 to 25 rpm/v which puts the DC 12V cutin rpm in the range of 300 to 425 RPM in a 6mph wind which suits a 3 to 4 ft prop running around 4 to 5 tsr.  As for the cogging, I think the best option for you would be to cut down the diameter of the rotor more to get the magnets away from the stator pols a bit more.  If you are using only 4 mags on the rotor then having the magnet length longer than the pole face length would help also.  The closer you match the magnet length to exactly match the pole length the worse the cogging will be.  The purpose of skewing the magnets is so that the leading and trailing edges of the magnets are not exactly alighen with the edges of the stator poles, and so that part of one magnet actually starts getting over a pole that is already being covered by another magnet.  If the magnets line up perfectly between (inside) the gaps between the stator poles you get alot of cogging.  You do not need to decrease the width of the magnets (dimension which corresponds to the thickness of the stator) as it will gain you nothing except loosing magnet area. A very small airgap between neos and the stator faces is bad for cogging.  Try to get the gap up to as much at 4 to 6 MM and it will do alot better on cogging, and not really lose much output. Ceramics are much more forgiving on geing gapped close, but you can have issure with them also.  Tou really need to get the cogging down to under 2 oz-ft for a 3 to 4 ft prop to be able to start it up in something less than a 8 to 10 mph wind.  The while fan conversion in my article runs about 1 to 1.25 oz-ft and the black motor at the end of the article (which used the ceramic lowes mags) run about 2.5 oz in.  Ive not been able to get it much less.

John
« Last Edit: February 20, 2006, 08:23:01 AM by johnlm »

zap

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Re: Box Fan Motor Conversion
« Reply #13 on: February 20, 2006, 02:39:20 PM »
Hey John, ghurd has been helping me with this thru email.


The magnet in the picture above is half of the original magnet, since then I've tried half again, cutting along the circumference, i.e. 1/4 of the original magnet. That reduced cogging quite a bit but also reduced the volts.


I got the armature cut down even more now and the air gap is probably not quite 2x as much as shown in the picture below. The cogging is less but I have a feeling it will still be too much for the vawt. ghurd's idea for cutting the stator pole face is also shown in the picture below. I might try this as a last resort, a bit tough to see but he suggested cutting the pole face off at an angle thereby skewing the pole face instead of the magnets. I still have some "meat" left on the armature but it's getting thin and I might have to just cut it all off and go with your wooden armature as you showed above. Cutting that armature down is a real drag!



I don't know the rpm but chucked up in the 1/2" drill I get 15vac and it will light a 12v tail light up. Fairly high rpm but not as high as the drill goes because so far the magnets are just temp mounted with superglue.


I unwrapped a few of the coils part way to see how they were wound and it appears they used 3 in hand, each a different gage. I only took off about 15 turns but all 3 seemed to stay right together. It's funny you mentioned adding coils over the existing and measuring the output of those, I just did that this weekend with a few different gages. I guess I need to figure out exactly what the rpm is of my drill so I can get some type of idea of rpm/v. If this things going to work on the vawt I'll need to keep the rpm's low. Still having fun though.

Thanks for the help John.

« Last Edit: February 20, 2006, 02:39:20 PM by zap »

johnlm

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Re: Box Fan Motor Conversion
« Reply #14 on: February 21, 2006, 07:38:52 AM »
Zap,

Sure wish you would use smaller pics.  With the large pics the post is now so spread out (width)  it takes me too long to go through all this on dial up.


I tried the 4 mag/ 6 pole approach and it does reduce cogging over a 6 mag/6 pole arrangement if the mags are close such as you have in your last pic.  But you have the disadvantage of 1/3 of your coils doing nothing at any given point in time.  I was impressed that on the white fan using a total of 12 neos (2 ea per pole X 6 poles ; 1 X 1/2 X 1/8 inch neos) I only ended up with about 1.25 oz ft of cogging - can easily be turned using only thumb and index finger.  But then I think the gap from the mags to the stator is about 4 MM.


You havent given any details about the resistance of the windings (or maybe I missed it) but if you are able to light up a standard 12 V tail light bulb the windings must be fairly low in resistance.  Almost looks like awg 24 wire on the stator.


John

« Last Edit: February 21, 2006, 07:38:52 AM by johnlm »

zap

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Re: Box Fan Motor Conversion
« Reply #15 on: February 21, 2006, 10:54:03 AM »
Sorry about the pic size John, I have become a little spoiled with broadband.  I try to post all mine at 640x480 so I guess you're talking about file size?  That last pic was one ghurd had sent back to me after he had doctored it up to show where to cut the laminates and I made the mistake of not taking it through psp before posting... sorry.


I wish I had some different magnets so I could try 6 on the armature but as you can see there's not much room left using 4.


I unwrapped one of the original windings and that one was indeed 3 in hand, about 96 turns, different figures from all my meters but looks to be about .3 ohm.  These are about 27ga, 26ga, and maybe 26.5ga?  Shorting the meter reads .5 ohm with meter leads and alligator test leads. Then to the coil for a total of .8 ohm.


I wrapped the empty pole with some old coils from a tube yoke from an old monitor, 4 in hand, 27 ga or so, 100 turns and that came out to .5 ohm but haven't done any spin tests yet.


The 15v and lighting the tail light was using 2 of the coils, the 12 and 6 oclock and like I said, not sure about the rpm.

« Last Edit: February 21, 2006, 10:54:03 AM by zap »

ghurd

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Re: Box Fan Motor Conversion
« Reply #16 on: February 22, 2006, 05:59:45 AM »
Zap,

Was the 96 turns, 3 in hand, for all 3 wires?  I mean was the green wire less turns?

Going from 300 turns to 400 turns, and wired in star, cut in should be ~130 RPMs. I think.

G-
« Last Edit: February 22, 2006, 05:59:45 AM by ghurd »
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zap

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Re: Box Fan Motor Conversion
« Reply #17 on: February 22, 2006, 09:17:46 AM »
G- on the coil I unwound all the wires stayed neck and neck, they all had the same number of turns, which is why I referred to them as "3 in hand".  The only reason I unwound that one was because I'd cut it's leads a little short at where the "buried ends" come out from under the rest of the coil.  It left very little exposed for further hook up.
« Last Edit: February 22, 2006, 09:17:46 AM by zap »