Mod cheap fan motor for alternator?

[FlyFishn]

All,

I have a fan here that the hub holding the fan blades on broke (cheap plastic, cheap fan overall). In looking at some ideas for converting AC motors it appears rotors can be drilled and magnets added to "convert" them to alternator/generator duty.

Will that idea work on this one?

If so - any idea on the amount of power I could expect out of it? If I could get 20-30 watts from it that would be cool, more would be better of course.

Any idea on the magnet pattern/quantity to use?

For reference the rotor is about 1-1/8" in diameter.

[Mary B]

Search on here for the ceiling fan motor conversions.

[FlyFishn]

I did some testing here with one of my 'scopes. It looks like the frequency is ~20hz when spun @ around 1600 RPM from a cordless drill on high speed (spec shows 1600 max in that range, not sure what the actual number is - just going off the spec sticker).

[FlyFishn]

Search on here for the ceiling fan motor conversions.

The coils on ceiling fans are a totally different configuration - they are open copper coil windings.

The motor on this fan uses what appears to be one coil "pack" (the black cube) and a bunch of laminated plates making up the stator that only has 2 loops of wire 180deg apart going through the laminations. It doesn't make much sense to me yet.

[FlyFishn]

Doing the math it looks like the stator is 2 poles.

Nshaft = (120)(f/poles)
Nshaft = (120)(20hz/2)
Nshaft = (120)(10)
Nshaft - 1200 RPM

1200 is a bit under the sticker 1600 RPM of the drill I used, but I would say the measured AC frequency from the 'scope is more accurate than the RPM of the drill being unknown.

Since there are only 2 wires it would be single phase. That would make sense. There is a 2 range switch for speed selection, so I am assuming that is changing the coils between a higher and lower turns count. But either way - in any "on" position there are only 2 wires connected. So that would be single phase.

As to the pattern of the magnets to add - if it is single phase then every 180deg of the rotor needs an opposite magnet pole. That would mean I would have to set the pattern symmetrically. I have enough magnets where I can do 4 rows. N, S, N, S. I think that is what I am going to try here and see what happens.

The magnets I have are the tiny ones from Harbor Freight. I can get 2 magnets side-by-side per row.

[mab]

Hi Ff,
I have to say I wouldn't bother trying to convert this motor; as a general rule of motor conversion to generator: bigger is better. With that motor I'd be surprised if you get more that a watt, and that would be at high voltage and very low current at high rpm. From memory, most people wouldn't bother converting anything less than 2hp / 1500w for a wind turbine, although as Mary referred to, some folks have managed with (multipole) ceiling fan motors.

You Don't say what your hoping to drive it with (what speed do you want it to generate at?)? It'll never make a wind turbine IMHO.

If you do want to try with this motor anyway then yes it's two Pole so your rotor wants one south and one north Pole. It's a 'shaded pole' motor so I think you would want to cut the two pairs of thick copper shorted loops that create the shaded poles, otherwise most of the power you do get will be lost as heat in these loops.

[FlyFishn]

You Don't say what your hoping to drive it with (what speed do you want it to generate at?)? It'll never make a wind turbine IMHO.

Well to be 100% honest I am wanting to try it as a generator on a bike wheel or a bike trailer wheel (probably the latter - I am working on a bike trailer project). A spindle of 3" diameter at 6mph would be a hair under 450rpm; at 20mph 4482rpm. A spindle diameter of 1.5" at 6mph would be a hair under 900 rpm; at 20mph 4930rpm.

Then there is the idea of taking a wheel off, adding blades, and setting it up as a wind turbine in camp.

There are 2 things I am not sure of -
1. How much power I can get out of this
2. How much resistance the generator/alternator will add, specifically to the moving bike rig, but the same question is there for adding blades - the resistance would determine the blade diameter.

If you do want to try with this motor anyway then yes it's two Pole so your rotor wants one south and one north Pole. It's a 'shaded pole' motor so I think you would want to cut the two pairs of thick copper shorted loops that create the shaded poles, otherwise most of the power you do get will be lost as heat in these loops.

Interesting comments. What is the purpose of a "shaded pole" motor? As opposed to having a "non-shaded pole" motor?

I didn't see this post until after I already had the magnets installed and epoxy setting up. I did 4 pairs of magnets, 2 per row, as I mentioned in my last post - switching poles each pair.

Once the epoxy is hard I will test fit and see about test spinning with the drill again.

[FlyFishn]

This is my third attempt at getting a post to show up.. let me try breaking it up this time.

The results with the magnets are less than spectacular.

With the copper loops cut I got 2v more on the peak-to-peak voltage. However, the waveform is very jagged. Might that be due to twice as many rows of magnets, perhaps, as I should have?

[FlyFishn]

The RMS voltage of the jagged waveform screen shot above (right column) is pretty much spot on with the rectified and filtered DC voltage that I got. I used a 22uF/100v electrolytic cap. It was not a scientific value, just something I grabbed from my parts collection to smooth the ripple.

[bigrockcandymountain]

You should only have 2 poles.  So N pole in one side and S pole on the other.  You can do 4 rows, just make them NN SS.