Author Topic: Motor Conversion Questions (Read 4671 times)

lforbes · « **on:** February 16, 2008, 07:39:03 PM »

Hello all - first time poster here.

I have performed one motor conversion in the past using ceramic bar magnets installed into slots cut in the rotor of a 1 1/2hp 3ph 8 pole (rewound) Baldor motor. It seems to work pretty well (I get about 1 KW from it at around 1400 RPM installed on a 12 foot turbine and "geared up" by about 4.5 to 1).

Anyhow I am now contemplating converting an AO Smith "blower" motor - 3ph, 4 pole, 230/460V using this time neo magnets and aiming for 230 V max output at whatever alternator RPM that happens at.

I have read many posts herein regarding motor conversion and it has been v useful reading but I am still a bit uncertain as to the following:

. What neo thickness would be most appropriate? I'm thinking 3/8 or maybe 1/2" (but am uncertain as to the possible problems of lamination saturation).

. I've seen here examples of conversions utilizing either round or rectangular neos. Rectangular would give better coverage but are perhaps more difficult to install(?).

. Rectangular neos can be purchased in 4" and higher lengths. I'm concerned however with the difficulty in handling such large & powerful magnets and am thinking perhaps lengths of 1 or 2" may be more appropriate(?).

. What would be the best glue for afixing the neos to the rotor? I have seen mentioned Loctite "super glue", epoxy glue and the cyanometh... type of glue. After the neos are glued, what is the best filler - epoxy or maybe polyester ester, or some other?

. Is it worthwhile or necessary to glue the magnets to a flat surface or is the round surface of a turned rotor OK?

Any guidance offered here would be much appreciated.

BTW, I have also just launched a blade pitch controlled 12 footer (pitch motivated by flyweights and restored by torsion springs, both on each of the three blade shafts). Seems to be working well so far........

Laurie Forbes

Calgary, Alberta

spinningmagnets · « **Reply #1 on:** February 16, 2008, 01:54:16 PM »

Dear Laurie, please post a close-up pic of your "Homemade Variable Pitch" (perhaps in a separate post?)

I believe there will be significant interest in that.

Have you read any of the "Zubbly motor conversion" posts yet? lots of great info and details there, and it sounds like the type of thing you're asking about.

vawtman · « **Reply #2 on:** February 16, 2008, 02:23:40 PM »

Whats the H.P and Shaft diameter?

If possible convert it to 12pl like Zub(r.i.p.)did to get your voltage.You will more than likely need to skew the stator if using rectangular mags.

Blower motors can be weak.Not sure on this one.

Flux · « **Reply #3 on:** February 16, 2008, 02:25:44 PM »

With neo magnets correctly shaped to the stator, about 1/4" Thick would probably be adequate. As you are unlikely to get the ideal ones then you will need to make do with things that don't follow the shapes properly. You will need extra thickness to overcome the extra air gaps.

If it is 4 pole, rectangular magnets are going to be rather approximate and you may have to use 2 or 3 per pole to get a reasonable shape. I suspect that no more than 1/2" thick will be needed even if the shape doesn't fit the curve too well. Small round magnets let you approximate the curved surface better but you loose out on surface area even if you gain on reduced air gap. Whatever you do you will far exceed ceramic magnets even at 1/4" thick.

Saturation of the core teeth will cause a bit of extra iron loss and may loose you a bit in low winds. It will not affect high wind performance, in fact it will help. I doubt that you will go far wrong with magnets 1/2" thick and even 3/8 may be ok if you choose a suitable shape. Narrow magnets will let you use more per pole and approximate the curve better but it is difficult to position magnets of the same polarity in close proximity. In that respect it would be easier to use 4" long magnets rather than hold shorter ones together.

How you hold them on is a personal matter, from the magnetic point of view there is no big issue with sticking them on a curved rotor but mechanically it is better to mill flats.

I wouldn't touch any form of superglue except for a temporary bond to hold them while you do something else. Many people fit the magnets into an aluminium or fibreglass cage and that provides a far more certain hold. Sticking with a first class epoxy or structural adhesive on to flats should be adequate. Filling the spaces with a reinforced epoxy would help even more.

You seem to imply that you are prepared to use gearing and the higher speeds mean that you need to be more careful with magnet bonding. Some choose to use magnets with holes and fit screws and that has some merit.

If you are worried about cogging then you also need to figure out what you are going to do about that and it may influence the fixing issue.

One thing to remember with gearing is that you aggravate the starting problem. Cogging can be virtually eliminated but iron loss may delay start up with speed increasing gearing.

If you use the 460v connection you will probably still need gearing to reach 230v with a reasonable sized prop.

I am sure others will be able to give you more help. Try to find all the good work that Zubbly did on motor conversions, there is a lot of good advice there.

Flux

lforbes · « **Reply #4 on:** February 16, 2008, 07:03:34 PM »

Spinningmagnets:

Yes, I have read the Zubbly conversion posts and found them v imformative. I may well adopt his fibreglass "cage" technique if I decide to go with round magnets.

I would be pleased to post pics of my blade pitch control project (as soon as I can figure out how to do it I will do a search first to see what others are doing in this regard.

Vawtman:

Sorry, should have mentioned the motor is 3 hp. Shaft dia is 7/8" IIRC. I too wonder about it being a "blower" motor - maybe be light on iron and maybe lightweight construction compared to others. Oh well, it was inexpensive - got it on e-bay but it hasn't arrived yet so have not had a chance to examine it.

Flux:

Thanks much for the additonal insight - reading it has improved my confidence level considerably.

I'm thinking now 1/2" thick magnets - probably round, maybe use a cage but am thinking about close packing them (that would be more laborious if they have to be stuck on one at a time but perhaps a quick setting "super" glue would allow a fairly fast completion i.e. stick 'em on one at a time and hold in place until the glue sets.

Yes - I am assuming there will be a gear-up required to get the required voltage (my current mill uses roller chain at 4.5 to 1 which seems to be holding up well).

I hear what you're saying about cogging and startup but I hoping the variable pitch blades will help in that respect (at rest they are pitched at about 60 degrees).

As you point out, it may be advantageous to use the 460 connections (with less required gearup). I understand from others that I should still then be able to draw up to about 2 KWs from this unit(w/o letting the smoke out) which should be enough for the next prop upgrade I plan to use this conversion for.

Thanks again to all who responded to my queries......

Laurie Forbes

Calgary, Canada

SparWeb · « **Reply #5 on:** February 16, 2008, 07:10:03 PM »

Howdy neighbour,

I live near Irricana.

You sound like you have some fantastic projects on the go.

I'm working on my second motor conversion. My first is up and flying, having learned much from the late Zubbly. So start with his bio, and the links that ensue from there:

http://www.fieldlines.com/user/zubbly

On my first, I opted for 12 milled flats on a rotor that I made from scratch. I bought magnets with holes in the faces, and screwed them down, thus avoiding the glue question. The end product works well, and I have no regrets.

On my second, I am learning that I really over-cooked the ham, and I can make the conversion in a simpler way by using the existing rotor. I am considering making two aluminum cylinders: one will be a "cage" to hold the magnets, and the second will be a thin-walled cover. I'm trying to use simulations to find out if the space between the magnets and the stator teeth can be large enough to have such a cover. If all this works, then I can use epoxy if I want, but it will just be a work-aid, the real structure will be the tubes that hold everything in place.

Pictures of a blade pitch control... me too, please.

DanG · « **Reply #6 on:** February 16, 2008, 08:18:17 PM »

I'm concerned however with the difficulty in handling such large & powerful magnets and am thinking perhaps lengths of 1 or 2" may be more appropriate(?).

Spend the money to get the length you will use - using multiple magnets aligned for same pole face will see them resist placement within 3/8 or 1/2 inch of each other; getting them in contact with each other for any period of time will best 99% of mounting schemes.

Get a section of magnet popping loose and 'flipping' within an air gap is an ugly occurrence, with a rotating rotor it is disaster.

ghurd · « **Reply #7 on:** February 16, 2008, 09:10:30 PM »

I would go with the round magnets.

Bar magnets will most probably line up with the core, and cog like its welded together.

If bar magnets are skewed, the gap at the middle of the magnet is much larger than the ends. I have a sketch, aw what the heck, it's only 3.6K.

The ends are touching the core. The middle is not.

If you are determined to use bars, I would use 3 pieces of 1" instead of 1 piece of 4". Staggered will reduce the cogging. Not sure how possible it is to get 4 pieces of 1" neo in a 4" space. They don't like being close together.

Don't use super glue.

About the first reasonable conversion I made, 4~6 hours after the neos were glued on, I showed my wife, and she plucked off a magnet like there was no glue at all.

It was a small conversion.

I use 24-hour epoxy. The 5 minute stuff is Not water-proof, only water-resistant.

I never tried the locktite.

Two cents...

G-

Flux · « **Reply #8 on:** February 17, 2008, 01:41:36 AM »

I think your coarse pitch at starting will minimise the start up problems and deal with iron loss. I would still make some attempt to decog , the worst case would make it very difficult to turn.

I am inclined to think that for 4 pole the round magnets would be a better solution. The rectangular ones would better suit a 12 pole where you could have one magnet per pole. Having the cage would greatly simplify assembly with magnets repelling, you really have to force them together and the cage will keep them from trying to get away.

I also infinitely prefer glue in shear rather than tension, Loctite high strength retainer grade would be adequate if you use the cage.

I would suspect that you would hit 230v near 700 rpm and you ought to get 2kW wind duty at that speed. If you geared more and connected for 230v then you could probably expect about 3kW but you may have trouble starting even with coarse pitch.

Is this pitch control a starting aid or does it also act as a speed limiter in high winds?

Flux

kurt · « **Reply #9 on:** February 17, 2008, 06:55:03 PM »

Zubbly used a machined aluminum cage on his later conversions in place of the fiberglass cage you can see it in some of his later conversion postings Dinges has also used this method on multiple conversions you mite wanna look at his work.

lforbes · « **Reply #10 on:** February 17, 2008, 06:56:32 PM »

Flux:

I will certainly try to decog based on comments here. Ghurd mentioned something I had not thought of for rectangular magnets - staggering them in place of skewing. The end result appears to me to be the same and the problem of excessive gap is avoided(?).

Your recommendation of round neos and a cage certainly makes sense and I expect now that is the way I will go.

Will have to experiment I guess with 230 vs 460 connections and associated gear-up ratio.

My pitch control mechanism is both a starting aid and overspeed limiter. The pitch starts out coarse and decreases as RPM increases, eventually going through "normal" pitch and, if wind is too strong, farther to go into blade stall. The starting point and rate of pitch change vs RPM are easily adjustable. Two things I like especially about it: RPM does not drop appreciably, if at all, going into stall - it pretty mcuh levels out. The other is there is no danger of overspeed if the load is lost for some reason.

lforbes · « **Reply #11 on:** February 17, 2008, 07:56:17 PM »

Hi Steven:

It's nice to find a homebrew wind enthusiast so close to home (the Bearspaw district to be exact) - maybe we can get together b/f too long and compare notes.

That's a nice clean setup you have there - I gather the prop bolts directly to the alternator shaft. Are typical motor bearings capable of handling the prop's axial thrust reliably?

With regard to your new conversion and the thin-wall aluminum cover, is it not v beneficial to keep the gap as small as possible i.e. the top of the mags almost touching the laminations? Your bolt-on neos might also suffer in that respect if the bolt heads widen the gap significantly. Maybe it makes no difference though if the alternator is larger than the prop can drive to full output(?).

Re the blade pitch control, I'm going to see if I can get some pics posted tonight...

Laurie Forbes

Calgary, Canada

lforbes · « **Reply #12 on:** February 17, 2008, 08:03:21 PM »

Dhurd & DanG:

From yours and others' comments it looks like either one piece rectangulars or round mags with a cage would be the viable options.

I am interested though in dhurd's suggestion of staggering multiple rectangular mags in place of skewing (should serve to reduce the flux gap). The problem still remains however of how to keep them close together. More thought required.......

Otto · « **Reply #13 on:** February 18, 2008, 11:00:04 AM »

Iforbes, you mention "Yes - I am assuming there will be a gear-up required to get the required voltage (my current mill uses roller chain at 4.5 to 1 which seems to be holding up well)". Could you give more details on your geared up system, what kind of gears and chain? Do you have any pictures of it? Why chain and gears over pulleys and belt? What about maintenance to the chain?

Thank you,

Otto

lforbes · « **Reply #14 on:** February 18, 2008, 10:16:56 PM »

Otto:

Below is an old pic of a previous 4 blade version - the alternator and chain drive part are what I am using now. As you can see, it's a two stage with overall 4.5/1 ratio. The 1st stage driver sprocket can't be seen but is on the main shaft just behind the blade hub. 1st stage is 5/8" chain and 2nd is 1/2" (could probably get by with one size smaller on each).

The sprockets and roller chain are cheapie, probably made in China, stuff bought at a local "Princess Auto" store here in Canada. Seems to be decent quality though and the price is right. I went chain/sprocket vs V-belt as belts tend to slip, have greater losses than roller chain and put greater side thrust on the shaft bearings. As for durability & maintenance, I keep in mind that roller chains have been used successfully on motorcycles for ages (where stress & strain and exposure to the weather are much more severe than on a wind turbine, if the drive is enclosed that is). Maintenance consists of applying one in a while a roller chain spray lube (you can buy industrial auto-lube gadgets but I think the spray lube will suffice, even if the stuff may have to be replaced eventually).

I'm thinking now of replacing the 2 stage setup with a single stage in the same ratio (can't recall why I didn't do it that way in the first place .

Hmmm - now I can't figure out how to attach a pic to a comment........

Laurie Forbes

Calgary, Canada

lforbes · « **Reply #15 on:** February 19, 2008, 10:25:28 AM »

PS Steven:

You wouldn't happen to have a lathe available would you?

Laurie Forbes

SparWeb · « **Reply #16 on:** February 19, 2008, 11:06:01 AM »

Hi Laurie,

Send me an e-mail if you want to meet up.

I really want to see your gearing and blade pitching for myself, too.

And... I can use the lathe at work after hours.

;^)

lforbes · « **Reply #17 on:** February 19, 2008, 07:43:14 PM »

Received my AO Smith 3hp 3ph 4pole motor today. The rotor is 3.725" dia and 4.0" long. The stator is 36 slot.

Ordered some neo samples, rectangular and round, to experiment a bit b/f ordering the whole batch. Wasn't able to find any 1/2" x 1/2" round so ordered 3/4" x 1/2". If 1/2" is removed from the rotor, there would be about 1.68" per pole of circumference available at the reduced radius(assuming neos at top should cover seven slots worth)so it looks like 1.5" of magnet width should provide pretty good coverage(?).

Noticed the windings in this motor are not expoxied in place so am wondering if this is a serious deficiency and, if so, would it be advisable to add some to it? Maybe that would reduce cooling capabiltiy however.

I've been contemplating Zubbly's cage method of neo mounting and am wondering if perhaps a better way would be to machine an aluminum cylinder to give a loose sliding fit on the rotor (to allow some room for glue) with OD equal to the unturned rotor. Holes for round magnets (slightly larger than the magnet to again allow room for glue)would then be added as per Zubbly's method. It seems to me this would be a stronger & more secure way of mounting as it would be solid metal but maybe that's overkill......

As always, all comments and suggestions are welcomed.

Laurie Forbes

SparWeb · « **Reply #18 on:** February 20, 2008, 12:54:24 PM »

I'm working on this myself. Can't say certainly yes or no, yet, because I'm still cranking through the details. An aluminum sleeve over the rotor can hold everything in, but if you want a reasonable, "machinable" wall thickness, you risk spacing the magnets very far away from the stator teeth.

My gut tells me that the 3/4" dia x 1/2" thick magnets will be just the right thing, though.

I'll have more answers this weekend when I can finish working though the numbers.

If the windings were not laquered, then you may have a re-wound motor. Maybe the only effect is that the wire can "hum" a bit when running.

lforbes · « **Reply #19 on:** February 20, 2008, 04:15:47 PM »

Stephen:

The type of Al sleeve I'm thinking of would be full thickness (from turned rotor to stator teeth less a bit). Holes would be drilled through the sleeve to accomodate the magnets a la Zubbly with the partial thickness fiberglass sleeve.

My motor is new so it doesn't sound like it would be a rewind - maybe just light construction (it weights 47 lbs which is the same m/l as my Baldor 1 1/2hp Motor.

BTW, I've just about decided in any case to go with 1/2" x 1/2" bar magnets - three per pole seems to make a nice fit with my rotor size and should give better coverage than round magnets. Won't have a sleeve to secure them with however.....

Laurie Forbes

lforbes · « **Reply #20 on:** February 21, 2008, 11:13:33 AM »

Otto:

Here's a pic of my gear-up mechanism as requested:

BTW, there's actually not as much rust as it appears as my camera seems to exaggerate the reds for some reason.

Laurie Forbes

lforbes · « **Reply #21 on:** February 21, 2008, 01:05:55 PM »

Am wondering how best to facilitate insertion of the converted rotor into the stator. There will be some serious attractive force involved here. For instance, 4x1/2x1/2 neos are listed as having 70 lbs "pulling force" on the magnet4less site. If I install 12 of these on my rotor (3 ea x 4 poles) that totals 840 lbs. Now, the actual force is going to be quite a bit less as the close ends of the magnets are a lot closer than the far ends to the stator, at least at initial insertion. Still I imagine 2 or 3 hundred pounds pull might be in the ballpark(?). Does anyone have a better estimate?

It sounds like a block&tackle might be useful along with rails to guide the rotor in.

I'm also concerned with the stator being sucked out of the case - it's not obvious how well they are attached on my motor.

Can anyone kindly describe how they do it?

Laurie Forbes

vawtman · « **Reply #22 on:** February 22, 2008, 05:13:49 PM »

Hi Laurie

My recommendation is to take time and study a bit more.You can't skew bar magnets on a round cylinder(sure you know that).If you skew the stator then yes.

Insertion is scary at first but once you do it a few times its not bad.You will never be able to suck the stator out.

Mark

lforbes · « **Reply #23 on:** February 22, 2008, 08:23:01 PM »

Vawtman:

Right, you can't skew bar magnets on a round cylindar w/o some loss of surface contact but you can stagger them which is what I may do (use 2" magnets instead of 4" and offset (stagger) one end of the rotor, 1/2 a tooth width or somesuch).

Re insertion, do you just hang on to the rotor and manually guide it in or does the attractive force require mechanical restraint of some kind? My existing conversion done with ceramic magnets (1 1/2hp motor) can be done manually easily enough but I wonder about larger motors with neos.

vawtman · « **Reply #24 on:** February 23, 2008, 06:27:51 AM »

Laurie,

On my conversion(5 hp) i used 16 arc segment mags(4 per pole)N48 and they were placed on the rotor like your thinking.It had slight cogging and it was amazing how that hampered the turbine it literally revurberated through the shaft,rotor and blades.It's torn apart now,windings and all for future playing.Working on a dual rotor radial now.

With round mags they are born skewed and easy to line up at the right angle across the lams.Thats how i would do it if i did another one.Or else buy skewed arcs.

For reinsertion i put a piece of styrofoam on the floor and put the stator on that,then grabbed it with my feet and put the stator in.

vawtman · « **Reply #25 on:** February 23, 2008, 06:30:13 AM »

Oops put the rotor in.Sorry

methanolcat · « **Reply #26 on:** February 25, 2008, 09:10:05 PM »

Laurie:

My 7.5 hp baldor conversion used 24, 2x1x.5 neo's totaling about 1920 lbs of magnetic force on the rotor. I'm not sure there is a set "safe" way of installing it into the case and almost impossible to get it back out, I did it like many others with good results "the throw it in method", kind of but not so much so.

I made a sleeve that just covers the leading edge of the magnets to help protect them on the way in. The sleeve is plastic, roughly 1" thick with a center hole that has little clearance to the main shaft (light slip fit).

I drilled and tapped the front end (blade hub end) of my rotor shaft 1/2-13, put in a threaded rod about 24" long so I had something safe to hold onto, far away from the mag rotor itself and the case so my hands were nowhere near the danger zone, I had already c-clamped the motor housing to a heavy steel table, put on thick welding gloves, and just tried to guide the rotor in, I just barely got the lead in sleeve started when all of a sudden the rotor was inside the case where it should be, happened so fast I didn't even see it but it worked.

I highly recommend safety glasses just in case a magnet was to shatter I have heard they can be dangerous when broken.

The thin lip can be seen in photo of the "lead in guide", very thin .025 thousandths thick as there is only .032 thousandths clearance each side between magnet corners and laminates.

I have heard of people using thin plastic like from a 2 liter pop bottle but it would be very problematic if it was to get jammed as the rotor was hyperspeed inserted. If thin plastic was used successfully it would be a bear to get out since the rotor will be stuck to the lam core with plastic in between it.

Matt

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Author Topic: Motor Conversion Questions (Read 4671 times)