Model generator build from scratch

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darwenguy

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Thanks. yes the winding machine has been essential, it must have made over 150 seperate coils now.
But i am pretty fed up with it to be honest, time to clear the bench and look at somthing els for a while.
Best regards.
Luke.
 

Madsciguy

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For simplicity divide by four, giving 3 coils ( at 120 degrees apart) and four poles (N,S,N,S). In one rotation, each coil would see two AC cycles, so 1000 rpm / 60 * 2 = 33.3 Hz (4 poles). So for a 16 pole design the frequency would be 133 Hz. For highest voltage connect the coils in three groups of 4 (series) in a "Y" three phase configuration.
 

DKGrimm

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For simplicity divide by four, giving 3 coils ( at 120 degrees apart) and four poles (N,S,N,S). In one rotation, each coil would see two AC cycles, so 1000 rpm / 60 * 2 = 33.3 Hz (4 poles). So for a 16 pole design the frequency would be 133 Hz. For highest voltage connect the coils in three groups of 4 (series) in a "Y" three phase configuration.
Your suggestion for wiring and your math are good, but I see only twelve poles on the rotor in the pictures. That would also work, and would give 100 Hz.
 

darwenguy

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For simplicity divide by four, giving 3 coils ( at 120 degrees apart) and four poles (N,S,N,S). In one rotation, each coil would see two AC cycles, so 1000 rpm / 60 * 2 = 33.3 Hz (4 poles). So for a 16 pole design the frequency would be 133 Hz. For highest voltage connect the coils in three groups of 4 (series) in a "Y" three phase configuration.
This makes no sense at all! And just seams a crazy ramdom statement to a question nobody asked. Dividing 12 by 4 would be 4 sets of 3 at 90 degree appart. And why would wiring it 3 phaze be sipmpler?
 

DKGrimm

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Your suggestion for wiring and your math are good, but I see only twelve poles on the rotor in the pictures. That would also work, and would give 100 Hz.
I just proved to myself how easy it is to put your foot in your mouth. 12 coils in the stator and 12 magnets on the rotor would put all coils in phase with each other, so no three phase output. The output would still be 100 Hz at 1000 rpm, though.
 

Madsciguy

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The question was asked back in Oct about a 12 coil 16 pole machine. Correct though, the pics seem to show a 12 coil and 12 poles, a single phase machine with clogging reduced by embedding the magnets which reduces the flux seen by the coils. A three phase design provides much less ripple after rectification (assuming dc output is desired)
 

Steamchick

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Hi Madsciguy. ( I like the descriptive name!).
Perhaps you can explain the comment about "embedding magnets"? My physics background suggests that building magnets into metal will effectively short-circuit some of the field...or using metal clamps the bridge N to S, or metal bolts....
This then poses the big problem for most non-technical folk of how to fix magnets into the rotor?
Do you have any clever ideas?
Personally, I favour copying the car alternator arrangement for the armature, with the "field generator" clamped between 2 claw-pole pieces? Is mild-steel or cast-iron preferred for these poles, as "magnetic" alloy irons are not so readily available?
Another question - I have a bicycle alternator, where the steel magnet rotor (10 poles) is on the outside of the stator. I propose to re-make the stator coil and pole pieces (rusted and broken) but thought to increase the field by adding neodymium magnets glued onto the pole pieces. Will this be a benefit, as the extra flux will saturate the steel, so will that prevent the extra flux being useful? Or will it simply use the permeability of the air for the "surplus flux"... I'm simply to old and addled to be clear in my head what will happen?
Finally, in a generator with alternating field poles, can aluminium be usefully used for the coil core? Or will the sinusoidal magnetic field simply lose all the power to internal circulating induced currents within the aluminium? (Back EMF.). I think those cores for coils should have high permeability and low remanence? But am I right thinking that mild steel has high permeability and high remanence? Aluminium, low permeability and low remanence, stainless steel low remanence and low permeability?
I.E. what metal must I buy to make iron cores for coils?
Thanks,
K2
 

Madsciguy

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Hi Steamchick,
First the magnet mounting question, yes, embedding cause flux lost and potential eddy current losses when running. I made finite element models to illustrate. This is a 12 pole, 12 coil simulation with a 1.5mm gap, 10x10x3mm neo magnets on a 100mm dia rotor.
embed.jpg

You can see the flux concentration at the magnet edges compared to surface mounting
surface.jpg

The flux distribution in the gap is reduced and is not as even across the face
flux1.jpg

SURFACE MOUNT

Flux2.jpg
.
EMBEDDED

This example shows that the gap flux (generated voltage) will only be reduced 15 to 20% by embedding the magnets 90% into the steel rotor. Flush mounting would likely cause a greater reduction. I typically use a pvc or wood jig to hold the magnets while bondingmagnets, using a 2-part epoxy with good shear strength. The magnets will always be strongly attracted to the rotor, so we only need to overcome shear and centrifugal forces. When bonding magnets, keep the bond line thin and always clean all surfaces with acetone (not alcohol) before applying adhesive.

If the magnet flux is generally constant I use a mild steel, for a stator and pole pieces, I'd use ductile iron or lamination.
Aluminum for pole pieces would change your generator into an eddy current brake. So no.

Using Neo magnets could improve the bicycle generator if the air gap is not too small. You would likely get higher voltage at the expense of increased torque requirements. Friction drive? = abrasion of sidewall

For coil cores, use ductile iron or ferrite

Hope that helps
 

Willyb

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Hi Madsciguy
Thank you for explaining this and adding the diagrams. The topic can be a little hard to grasp especialy as one gets older. I'm planning to design and build my own model generator in the near future.
Cheers
Willy
 

Steamchick

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And just one more pic, also tried some green paint for a change :)
Still waiting for the little brass wingnuts to finish these.
View attachment 125911
Hi Luke,
I was loking for your website - but failed to find it (stupid me??) - and found this Utube clip. I guess you are NOT Myfordboy?
I suspect your generator is a whole lot more powerful than his...?
Where can I go with a view to purchasing a set of castings?
Thanks,
K2
 

Steamchick

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Hi madsciguy. Excellent explanation. The generators I fiddle with are for model steam engines. Old Sturmer Archer hub-dynasty are cheap when broken. Usually a broken wire or rust instead of laminations.
The 10 pole pm rotor is usually good, so just needs a new stator, so I'll have to find some ductile iron.
Thanks.
K2
 

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