4 arm stators

[Q]

I opened up a bunch of PC fans today and found nothing but 4 arm stators. I was hoping for a nice stator like Lucien found, but no luck. :(

I am pretty sure these 4 arm stators can't be used for our three phase motros, but I thought it doesn't hurt asking. Is there anything I can do with them?

[LBMiller5]

Q,

The stators I got were from an old SCSI Hard Drive. All of the PC Fan stators are 4-pole style, and you are right, they cannot be used with a 3 phase controller. All 3 phase motors have a number of poles that is a multiple of 3, such as 3, 6, 9, 12, 15, etc.

The PC Case fans use a 2-phase Free-Running type of control system. There is a little hall effect sensor that senses the position of the magnet ring, and switches the 2 coils on and off based on the angular position of the magnet. These types of motors will spin as fast as the voltage sent top them will allow. The speed can be controlled using a standard brushed type of speed controller.

Here is a photo of the Hall Effect switch that shows its location inside the fan. You will notice that it is located right in the middle between 2 of the poles.

http://innov8tivedesigns.com/rcgroups/HallSwitch.jpg

The Hall Effect switch that is typically used is the APX-9140. This part has a hall effect sensor and a pair of transistor switches that will turn 2 coil phases on and off depending on whether the sensor "Sees" a North magnetic pole or a South magnetic pole next to it. There are 4 legs coming out of the part. The one on the far left is for +Voltage and the one on the far right is ground. The 2 middle legs are the outputs and are opposite polarity, when one is on, the other is off, and vice-versa.

Here is a data sheet on the APX-9140 part.

http://innov8tivedesigns.com/rcgroups/APX9140A5.pdf

You could re-wind the stator with larger wire, but since the switch can only provide about 400mA of continuout power, you would have to boost the current handling of the hall effect switch with a pair of power darlington transistors or FET's to handle the lower resistance of the new windings. With better magnets, these could be made to put out a lot more power. Maybe I will try one myself and see how much more power one could be made to produce.

If you have any other questions, post them here and I will try to answer them.

Take Care!

Lucien

[Q]

Thanks Lucien.
I kind of knew it would come down to this. Pitty though. Plenty of stator sizes available in PC fans

I got some very good stators out of my old PC junk I finally cleaned out. A tape drive and a 3.5" floppy drive gave me some very good ones. 12 arm statoes than are mounted with 3 little screws. I can just inscrew them, rewind them and mount them back. Luck has it they both use ball bearings. Hack, I can whip up a pretty good motor in about an hour if I'm lucky with the magnets I have in stock. :D

[ScubaSteve]

Nope you can run 'em in a 3-phase configuration. Think outside the can. :wink:

Wind three separate stators as ONE-PHASE each. Place 'em on 1 bearing tube each rotated 120 degrees. Wire in series. Enjoy. Basically you just wound a 12-pole stator with 3 times the amount of iron (or 1/3 the amount of copper depending on whether or not the glass is half-empty or half-full). :D

I can't speak from experience on this, but I know it's been done successfully. Maybe it could show promise for small hot wind motors that would normally see significant hysteresis losses?

[Q]

Hmmmmm, you got me thinking here Steve. :-D

It might indeed make a very nice motor for a micro EDF. :-D
I'll see if I can get three identical stators from the ones I scavanged.

[ScubaSteve]

I'm more interested in the reduction in losses. Am I off the beaten path maybe? If the problem is iron saturation, you can basically increase the saturation "limit" by three by using stators wound in series, right? Heck you could do the same thing with 9 pole stators and end up with monster torque. :roll:

[Q]

Yep, I was thining the same thing. More tests to do. Soooooooo little time. Pffff I need to go on pention leave. Sadly enough that's a financial decission I can't take yet.

[swatson144]

Seems maybe we are forgeting all the wraps top and bottom that would make this a very tall stack? with a lot of wasted space? Seems it would only work with a 4 pole so the magnets don't overlap the LOOONG hammerheads? Hmmm 4 pole low turn, what can we do with that :shock:

[Q]

I was thinking of using this kind of motor in an EDF unit. The thin motor would be a big advantage.
You only use magnets for each individual stator, not over the total height of all stators.

[Q]

Come to think of it. Would I use 3 or 5 magnets per stator?

[ScubaSteve]

Remember, regarding the magnet configuration you need to treat your stack of stators as ONE STATOR. Pick whichever config you want for (if you're using 3 4-pole stators) 12 pole stator. If you imagine compressing the stack of stators into one common stator, it'll likely clarify any of the questions you might have. I believe the example I saw had a single magnet config, not 3 rows.

swatson, you really won't have that much room in between - remember that the main application of something like this would be an EDF or "hot" motor setup where you aren't really using that many winds.

This definitely calls for more tests.

[Q]

Yahoo, got three identical 4 arm stators. I'll keet my eyes peeled if I see a suitable iron pipe/tube.

[SkyCobra]

ScubaSteve:

With the GBL 9 tooth stators you would line them up straight on the tube, then have the magnets straight on the can... no offsetting anywhere.. correct ? Sounds nice and clean to me.

Confusion sets in with the "more iron" . Let's say I have a motor with 9 25mm GBL stators = 15mm or "triple" motor.

Motor #1 would have all 9 stators stacked together like a standard GBL motor. This would give me one wire wrapped around 9 stators times 3 teeth. (27) .

Motor #2 would have three stators stacked together in three seperate groups. This would give me one wire wrapped around 3 stators times 9 teeth ( 27).

They seem to be equal to me. This is interesting stuff, I have stators and possibly a can to try to attempt this. The problem I see is that there seems to be alot more work involved in Motor #2 construction. Also, how do you re-wind this type motor after it's put together ? That middle stator group would be a bear to re-wind.

Hopefully if time allows, I'll try to build and test one of these motors.

Skycobra,

[Q]

Cobra,
we are refering to a usablility for 4 arm stators found in 2 phase PC fans. As our motros are three phased, you have to use three stators and dedicate one stator to each phase or mix and match and treat is like a big 12 arm stator.
Your statement is in regard of a tripple stacker. You don't get any advantage there of course.

[ScubaSteve]

Actually it's still earl AM for me but I believe what he's thinking about doing is the same as you plan to do with a 4-pole stator, only he wants to do it with a 9-pole (which you CAN do).

Yeah it'd be a PITA but you 'should' get triple the torque from using 3 9-pole or 12-pole stators skewed 120 degrees as compared to a single 'flush' mounted stack of stators. Remember, they'll be wound individually, but then the total stators are wired in series, so the ESC will see ONE stator. So will the rotor. Thus your 3 9/12-pole stators become a single 28/36-pole stator. :shock:

[Q]

Hmmmmmmmmm, might be useful to get a motor that has enough torque to run a heli in direct drive without needing a HUGE inefficient stator.
Most bigger helicopters need a tripple stacker anyways.

Now I'm wondering what kind of winding scheme you'd use with a 120 degree skewed tripple 12 arm stator (virtual 36 arm stator) and how many poles would go with it.

[ScubaSteve]

Man, where's the link to that handy winding scheme chart when you need it... :?

[swatson144]

Steve, John has taken pics of his beautmous motors on that chart and soon he'll remember he knows how to multiply... :P

[Q]

Man, where's the link to that handy winding scheme chart when you need it... :?

Here's one : http://www.powerditto.de/Kombinationstabelle2.html

Goes only up to 18 though.

[SkyCobra]

Yes, ScubaSteve has the idea. I've heard these "offset" motors have more torque. I was thinking that I could get much more torque at the expense of a little lenghtening of the flux ring/shaft/bearing tube combos. In addition, I was hoping the winding of the stators would be simple, but I'm not sure after looking at that winding table. Somebody please tell me that winding one stator with one wire in one direction on all teeth - solder three ends together, other three wires to ESC.......

Q

I've disassembled about 40 fan units with 4 pole stators. Seperating the stators produces many holes in your fingers, then putting them back together and insulating them... man, lots of work. I'm just tryng to lessen the pain ! Although that bag of 300 laminations seems to talk to me as I'm working nearby.

[ron_van_sommeren]

Nope you can run 'em in a 3-phase configuration. Think outside the can. :wink:

Wind three separate stators as ONE-PHASE each. Place 'em on 1 bearing tube each rotated 120 degrees. Wire in series. Enjoy. Basically you just wound a 12-pole stator with 3 times the amount of iron (or 1/3 the amount of copper depending on whether or not the glass is half-empty or half-full). :D

I can't speak from experience on this, but I know it's been done successfully. Maybe it could show promise for small hot wind motors that would normally see significant hysteresis losses?See
http://www.rcgroups.com/forums/showthread.php?t=249953