Author Topic: Questions for the conversion guys (Read 3527 times)

rotornuts · « **on:** January 08, 2005, 01:07:24 AM »

O.K. It's time to convert a motor. I can't do any more blade experiments till I have an output to measure. I considered an axial and made a 5" disk with 10 - 1"x1/8" x 2 deep disk neos on it. Had fun playing with coils but for experimenting I don't want to build an actual axial so I've decided to convert a small induction.

I'd like to keep it simple so to avoid having the rotor turned I thought perhaps I could just drill 1"+ holes 1/4"+ deep to drop 2-1"x1/8" neos in.

Here's a pic of the general idea. Any thoughts?

Jessum Dumguy · « **Reply #1 on:** January 07, 2005, 07:09:05 PM »

I can't tell for sure from the pic but the roter surface looks

like it's steel of some sort ( looks like rust on the surface ).

If so I'd think you'd loose alot of the magnets flux into

the steel at the surface before it ever made it to the coils.

.

Garry · « **Reply #2 on:** January 07, 2005, 07:11:23 PM »

Drill a hole in a scrap piece of steel and place two magnets into it. You will find that most of the flux is short circuited by the steel on the sides of the hole and almost no flux comes out of the pole face. Are you anywhere near Northern Oklahoma?

Garry

rotornuts · « **Reply #3 on:** January 07, 2005, 07:25:20 PM »

This isn't the motor I would convert but it's a 1/3 hp induction motor and that's a steel laminate rotor. I'll try the experiment with the steel plate.

I'm curious what the flux path would look like. Can anyone do an image?

monte350c · « **Reply #4 on:** January 07, 2005, 08:48:15 PM »

I'm curious too. I did a simulation in FEMM a while ago for this idea.

The pics below are as follows. The bottom plate of steel is .75 " thick. The magnets are 1 inch diameter and .25 inch thick. The top plate of steel is .375 inches thick and the airgap is also .125 inches.

The lines in the pics on the left magnet from left to right:

The first column is the line number, the second is for submerged mags, the third for suface mags. This is for the flux in the center of the airgap.

(This without the pre tag is going to be messy)

Line flux flux

5115 7142
7005 7157
7703 7781
7962 8074
8159 8116
8278 8154
8338 8174
8341 8156
8289 8140
8163 8066
7982 7919
7709 7842
7299 7403

Pic 1 the submerged mags:

Pic 2 the surface mags:

It looks like the results will be pretty close. But it would probably be a great idea as suggested to try drilling a couple of holes and dropping the mags in, and compare with a couple of mags mounted on the surface.

Not being a machinist I don't know how to make suitable flat bottom holes? Anyone know a way, or is this a trip to the machine shop?

Lots of fun in any case

Ted.

rotornuts · « **Reply #5 on:** January 07, 2005, 10:14:46 PM »

Allright I did the experiment. I checked to see if I had a 1" bit and came up empty handed but found a salvaged 14" overhead sawblade with a 1" arbour. With a little filing I was able to coax the neo into the arbour and it happens to be the same thickness as the blade. here's the pic

It was right after this picture that dumb dumb(me) dropped the digital on the concrete floor so no more pics for now.

I placed the blade with magnet across two chair backs and proceeded to hang stuff off the magnet. First a body working dolly then the live end off my wood lathe(the whole thing). Lacking a single scale in my house I decided I have to try something someone else can wieght so I put the above motor back together and tried it. Too bad it didn't hold. But wait! I realized I had no metal backing only metal around the neo so I slapped a 2" cutoff of 2" steel shaft over the neo and tried the 1/3 horse motor again and to my surprise it held. Anyone have any idea haow much a 1/3 horse GE induction motor wieghts? Can't be "leaking" that much flux.

I'm sure jaquesm could tell us the best bit to use for drilling the hole. Perhaps for a drill press though as I don't have a milling machine.

If I get the camera working I'll post pics.

rotornuts · « **Reply #6 on:** January 07, 2005, 10:27:17 PM »

Monte, It seems the air gap of the submerged mags contains about 5% more flux!

BTW cool simm program.

Jerry · « **Reply #7 on:** January 07, 2005, 11:22:50 PM »

Hi Rotonuts

What are the specs of the motor in the piture? Its a 4 pole single phase I can tell that.

I can tell you what kinda power I get from a motor that size if you can give me some specs?

I'm doing a bar magnet conversion right now with some washers from Lowes. All you need is a hacksaw and some epoxi. Not all that hard.

JK TAS Jerry

iFred · « **Reply #8 on:** January 07, 2005, 11:24:14 PM »

I disagree with submerged neos, have done this, did'nt work. Submerged neos short the magnetic flux to the rotor caseing, good by magnetic forward going path! don't beleive it, try a simple experiment with just a peice of metal, a single hole and a single neo, then put some paper on top and sprinkle some fillings on top, see what happens.

My suggestion is lathe the rotor to the depth of the magnets and maybee a hair more, then glue them on in pairs or triples in rows. make sure that you equal out to four poles total for original listed motor less then 1800 rpm's. Above this use 6 or 8 poles. You can still add the twist to reduce your cogging maybee.

iFred · « **Reply #9 on:** January 07, 2005, 11:25:31 PM »

Oh yea, almost forgot... SPACE between magnets is really importent!! space them.

rotornuts · « **Reply #10 on:** January 08, 2005, 02:16:03 AM »

Jerry, it's a two speed 1/2-1/15 115v 7/3.3 amp 1725/850 rpm. The above motor would need a rewind as I've butchered some of the windings for coil experiments. I think I'll find another to convert, probably the same thing. I'm curious if I can make this hole thing work. Any expected power ratings would be appreciated as I might just go ahead with sinking the neo's and compare output to what you average for a motor like that.

Thanks for the help.

rotornuts · « **Reply #11 on:** January 08, 2005, 02:27:21 AM »

iFred, thanks for the help. I did the paper and filing thing and honestly the patterns where exactly the same for submerged and surface mounted - concentrated entirely around the circumference of the magnet.

When you tried this did you drill right through the metal then insert the magnet with nothing behind it. With my sawblade experiment above, placing a block of metal behind the magnet significantly improved things just as it does with a surface mounted mag. below is an drawing of the contraption with and without the block (camera hit the concrete and doesn't really work anymore, oops).

tecker · « **Reply #12 on:** January 08, 2005, 02:35:35 AM »

The steel will gobble up the flux and dissipate it in all directions and pull flux from the top pole to the bottom the null point in the magnet will be move into the steel and spread out a little pole will be left right on top of the magnet face but but the flow through the stator from the two adjacent magnets is so slight it's negligible

DanB · « **Reply #13 on:** January 08, 2005, 08:36:07 AM »

I think that the flux leakage from magnets which are buried in steel becomes worse as the magnets become smaller (less surface area). With large magnets like I used to use (and Jerry uses) - its almost a none-issue. With small 1/2" diameter disks it would be a serious problem. With these 1" disks I suspect it will be an issue, but perhaps less - so.

Flux · « **Reply #14 on:** January 08, 2005, 08:53:32 AM »

Yes the size and thickness of the magnet matter. It is never a good idea to bury magnets but with large magnets and a thin section round them the loss may be small.

With these little magnets the loss will most likely be over 50%. Not only is there direct loss across the magnet, there is also loss from the induced stator back to the steel on the rotor unless it is saturated.

If you can't mill or turn it down go back to the hacksaw and steel washers or something. Drilling flat bottomed holes is a pain anyway and will be even worse as you drill a mixture of steel and aluminium cage bars.

Flux

Jerry · « **Reply #15 on:** January 08, 2005, 10:20:31 AM »

I converted a simular 1/2 hp 6.7 amp 115 volt 1725 rpm motor. I used 4 of the old #29 curved NEOs.

It did 10 mph 5 amps, 20 mph 10 amps and 30 mph 25 amps. This was with stock coils and coil reasignment. This was with a 49" 4 blade prop.

JK TAS Jerry

jacquesm · « **Reply #16 on:** January 08, 2005, 10:44:14 AM »

I'll rise to the bait

I've put drills in my mill, so in this case if you have a drillpress I'd not hesitate to put an endmill (with some kind of an adaptor) in the drillpress.

Go easy and clean out often. Make sure you get a 4 flute endmill. That will give you a very nice flat bottomed hole.

I'm not an authority on flux leakage, but I think it may be less than you'd think by the simulation pictures, your airgap will be very very small by doing it the way you suggest, assuming you keep your holes just deep enough. A compromise that would work even better would be to turn 1/8 of an inch off the surface of the rotor, then drill the holes.

that way you get some sideways support to avoid the magnets moving due to forces acting on them when you start making power, and you'd get rid of some of that flux leakage, which is always better than having it, no matter how much effect there will be.

Adapting an endmill for use in a drill press is easy, you can either ask a machinist to turn it down for you to a size that your drillpress can handle (most drillpresses will do 1/2" bits, but check to be sure), or you can make a collect holder for your drill press. Some drill presses have replaceable chucks, with a taper, and you should be able to find a collect holder for that taper.

do wear those safety glasses

jacquesm · « **Reply #17 on:** January 08, 2005, 11:03:41 AM »

that's very true flux, the induced losses are probably more where it's at than any losses on the surface per se (at least not with a 1" magnet).

iFred · « **Reply #18 on:** January 08, 2005, 01:16:15 PM »

I have posted on the concept of magnetic shorting, please feel free to post comments.

monte350c · « **Reply #19 on:** January 08, 2005, 07:48:35 PM »

Yup - it would be interesting to know what's going on in there, especially if some of the original rotor bars, and the shorting rings at the ends are still in place.

The rotor might be doing what it was designed to -

Suppose it's possible the induced current in the rotor bars might cancel out the magnets, or at least greatly diminish their effect?

Maybe better to start off with a fresh piece of steel like Jaques' conversion motor in his diary.

Ted.

rotornuts · « **Reply #20 on:** January 09, 2005, 01:05:33 AM »

Thanks everyone for the input and I can see the best way to solve this one is to build it and compare to some of the stuff jerry has done. Thanks jaquesm I'll head to the local machine shop and see what they can do for me. I'm intriqued by the notion of induced losses, hadn't thought of that. Did the filings experiment again and drew an image of the results.

not sure what this means but I can assure you this arrangment held the wieght of a 1/3 hp induction motor of a 1"x1/8" neo. I tried the motor with a metal backed mag and it held about the same (I was able to "shake" the motor off both arrangments with about the same force).

Trivo · « **Reply #21 on:** January 09, 2005, 03:29:24 AM »

I am in the process of a 1 hp conversion and have a rotor with mags set in to it with the ends on, so i took a reading of 1 coil @ 300rpm and got 3.9VAC then machined the ends down and did a re test and got 3.9VAC so i dont think i will worry about it to much

jacquesm · « **Reply #22 on:** January 09, 2005, 07:02:10 AM »

Ah, but you will only be inducing currents when current is flowing !!

So, in order to see if this really matters you have to first run a test with a full rotor of 'embedded' magnets, measure the power at several different RPMS, then do it all again with the rotor turned further down...

rotornuts · « **Reply #23 on:** January 09, 2005, 01:39:53 PM »

This sounds like we may be able to solve or exasperate some controversy here. I'd like to try both ways on the some rotor but a problem pops to mind - how to get the magnets back out of the hole? I suppose one would have to predrill smaller holes on the circumference of the larger holes to privide access although what would this do to the flux path. aaarrrggg.

Jerry · « **Reply #24 on:** January 09, 2005, 08:08:29 PM »

Get an another armature exactly the same and build 2 then compair.

JK TAS Jerry

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Author Topic: Questions for the conversion guys (Read 3527 times)