Model sized generator parts

[old-and-broken]

My grandson visited last week(6 yrs old) and wanted to use some of my tools and 'do something'. I gave him a screwdriver and socket set and found a chair to sit in after pointing out a defunct box fan. I told him to take it apart and see what it was made of.

These are the parts he found.

I've cleaned up the stator iron by stripping the coils out. Did a little playing around with configurations and noodled about with some measurements.

I think I can turn these into a nice sized model generator by adding some magnets and winding some new coils. DC would need a commutator, but AC can be easily rectified here in the modern age with diodes to provide DC level, and along with a voltage regulator IC could be hidden inside somewhere.

What do you guys think?

The source of the parts is one of these.

 

[mu38&Bg#]

With 16 slots it must be wound single phase. It should make a decent generator, and could be capable of at least the rated power as a motor.

Greg

 

[old-and-broken]

Winding it as a single phase would waste valuable stator space. I opted to go for a 12 magnet-4 phase winding that would utilize all of the available winding spaces. Magnets will be only 1/8 inch in width and either 1/16 or 1/8 high. Haven't got that far yet.

 

[mu38&Bg#]

You could wind every slot as single phase. You would use a different number of magnet poles. 4 phase full wave rectifier for 4 phase windings?

Is the intent just to make voltage and a few mA or to be as efficient as possible?

Greg

 

[old-and-broken]

That was quick. The magnets were waiting for me on my front porch when I got home today. Since I haven't decided on the size yet, I
ordered both sizes. Next I have to figure out a mounting method for the magnets. milling some flats on the rotor and encapsulating the
whole in a clear epoxy resin when the magnets are properly positioned? Glue them in place first for good measure? Probably both.

As for a single phase winding, I can't think of a configuration that wouldn't have a rather noticeable cogging effect from the magnets all
lining up at a high attraction point and having to break free to move to the next attraction position. If I use fewer, wider magnet poles
to reduce cogging effects, then I will need a higher RPM rate to achieve an equivalent rate of magnet field alternation. With twelve
magnets I am effectively getting 6 full cycles of electric current from a single 360º rotation out of each phase. This should let me run at
600 RPM and achieve the same 60 Hertz frequency that single phase, two magnetic pole operation would yield from 3600 RPM rotation.

I'm pleased to have your interest in this 'drawing board' stage plan Diesel pilot. If you have an idea that I'm overlooking regarding single
phase winding schemes, please continue to present them. I may be missing something that is obvious to you. I do that kind of thing all
the time.

 

[mu38&Bg#]

The first question that should be answered is how much power do you want? If DC as mentioned previously, the frequency doesn't really matter.

I've been working with 3 phase brushless motors and generators. You can use many combinations of poles, slots, and winding scheme to achieve the desired output. If I was do single phase I'd wind every stator tooth in alternating directions and use 16 magnets. If cogging really was a concern I'd use a skewed (staggered) magnet to reduce it.

At 600RPM simply using epoxy to glue them to your rotor will be enough. The small magnets being used will limit power output.

Greg

 

[Lakc]

I often wondered about how the magnetic field overlap works. Does it just produce waste eddy currents?
I just need to sit down with a suitable quantity of adult beverages and think that one out someday...

 

[mu38&Bg#]

The fundamentals of motor design are fairly simple. It's the details to get the specifics of say torque ripple, harmonics, efficiency, etc., that are that are killer.

Jeff, basically any design deficiency results in reduced efficiency from the motor/generator. Small details like lamination material and copper fill ratios can result in the same physical motor being capable of several times the power output. Thing like the skew to reduce cogging only reduce efficiency by a few percent, but if low/no cogging and torque ripple is more important it worth it.

Greg

 

[old-and-broken]

next step was to make some kind of form upon which to put the copper windings. My hope is to fix the wire to the form using superglue or perhaps some type of epoxy then to simply 'slide' the forms into place on the stator iron projections. Before I can do this I need to perform one machining operation which will remove the 'shoe' at the end of the stator iron projections. That will be next.

I didn't want to have to order anything special, so I dug out some ABS plastic sheeting I had stored away. I'm hoping its 150º to 160º F temp limit won't be exceeded. (fingers crossed). It is 1/64 inch thick and I had to score the surface with a razor knife to enable it to be bent around a 90º corner.

Lastly, I'm going to try the image hosting site gamble. I've maintained file names so I can go back and restore the photos should the inevitable happen

 

[AussieJimG]

I will be following this with interest. I never did understand electric motors and generators and maybe this will fill some gaps.

Jim

 

[old-and-broken]

I'm sadly unable to sleep tonight. Spent some time modeling the stator and rotor in sketchup.
The stator will require machining to remove a small amount of material from the inner most portion.
A final diameter of 1.875 will allow me to use the 1/16 thick magnets and leave an air gap all around of approx. .015" (1/64). Leaving me a quarter inch for the windings.
Everything is finalized as far as I can go on paper dimension wise.

I'll pick up this project in a new thread in the appropriate forum and provide links between this thread and the new one. Look for an update
next week.