To generate elect. is it better to have the coil spin within the magnetic field or magnets spinning inside the coil

Which is better for making a homemade generator powered by the wind? Tesla model suggests coil spins inside of magnetic field but most electronic sites suggest having the magnets spin inside the coil windings. Are more amps produced by having the magnets spin inside the coil windings instead. Couldn't you just use most any (machine pre-wound) coils from motors rated from 1 - 5 hp. and make your own rotor where the magnets spin INSIDE the existing windings from those motors? Helpful to me since they are already rated with rpm speed. Why would you make your own with so many used motors available?

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squirt85008 years ago
It depends on whether you want AC or DC, but if you are talking about efficiency than having the magnets inside would increase efficiency because you wouldn't need brushes. Yes you could use pre-wound coils from motors because they are most likely wound tighter than you could wind them but finding a cheap donor motor would be hard. As for the RPM's, I would try to gear down the spinning armature to closely match the RPM's
Just wanted to let you know that brushes are used on DC motor and generator types on all AC motor/generator types are brushless.The reason it is more efficient to spin the magent inside the coil is because a solid magent is easier to secure than multiple windings. Plus as the coil size increases you would have to extend your magentic field to allow a bigger coil to fit within it, thus weaking the field, as if the magnet were to spin the magnet size would stay the same and as the extior coil got bigger the magnetic field would not have to increase, weakin, or be adjusted. Hope this helps.
SpeedRacerTerri (author)  squirt85008 years ago
Thanks, this is what I thought. I have access for all types of motors from 1/3 hp up to 5 hp. Have been collecting them but when I watch utube video's they throw away the original wiring saying its useless. They obviously use stranded wire whereas I bought solid but from what I understood is that if motor is rated for say 3400 rpm's then my unit would need to spin approx 3700 rpms to generate electricity (I have 5 all rated differently) anyways no matter how fast it spins due to the wiring of the used motor thats all i'd produce. I suppose thats why they didn't use the machine wound. Does that sound about right? Thanks again.
This isn't entirely accurate. Whether the builder gets AC or DC out depends on whether they use multipole magnets, and whether they use a rectifier circuit outside the generator. The comment about brushes is a good one.
SpeedRacerTerri (author)  kelseymh8 years ago
Creating AC current, turning it into DC to charge battery bank. I had planned on using a voltage regulator as well.
Single pole or multipole, a magnet inside HAS to generate AC. The ONLY way to generate DC is with a commutator on the armature, because we don't have magnetic monopoles. Steve
Wait a second. Make a cylindrical dipole magnet, and put it in the center with the spindle along the dipole axis. When you spin it, you still have field lines cutting through the coils, but their orientation doesn't change with respect to the coils. Shouldn't that produce a steady-state current.

No wait, that's impossible. I = d(B.l)/dt. If B isn't changing, whether the individual fictitious "field lines" are moving or not, then you don't get any current.

Yeah, okay, so I was being dumb.
Kiteman8 years ago
Either works. Spinning the magnets means you don't need to have any rotating electrical connections, so maybe that's the way to go for an easier build?
jeff-o Kiteman8 years ago
That makes sense to me. Anytime you can eliminate a mechanical connection (like commutator brushes) you can increase the longevity of the system by a bit.
SpeedRacerTerri (author)  jeff-o8 years ago
Quick thought, wondering if pvc, scaffolding pole 1 1/2" or a copper pipe would be best to hold up my turbine. I'm working on a vertical axis designed windmill. Most show using pvc sch 80. I have plenty of scaffolding available but wondered if you could bring the negative electrons down thru the pipe and harness it there? Hope that question makes sense, just crossed my mind as I read about using welding wire 1 1/2" due to shaft twisting problems w/ wiring.
Why? The generator will be either on the top or bottom of the turbine, with a pair of wires sprouting from the side of the generator. You'll probably use ordinary household wire to connect the generator to the charge controller. So, there's no need to use the scaffolding as one of the conductors.
SpeedRacerTerri (author)  jeff-o8 years ago
Thanks !! Why? Heck if I know, thats why I asked (heehee) I appreciate it. I think I was just thinking about connections - if I spun coil inside of magnets, that created a magnetic field that would go down the pole?? then maybe I could harness it there. Just wondering if it would work like that. Tring to absorb and understand as much as I can. Thanks again. Terri
Nope. I don't think that would work at all. Best to stick with a separate generator either directly connected or coupled with a belt drive.
Also, if you do use scaffolding, and the resulting structure is relatively high, make sure it is well grounded to help eliminate lightning strikes.
SpeedRacerTerri (author)  Kiteman8 years ago
First time asking a question while learning forum etc. Its almost 2 am - first chance I've had to get online without interruption. Blown away with such intelligent answers. Sure to be up all night reviewing them. Thanks to all. T.
seandogue8 years ago
What matters is that there is a time varying magnetic field applied to the wiring.. that's where the current is generated, wrt to electrical generation, that is all that matters. The rest is, to the best of my knowledge, driven by manufacturing costs, current delivery, and maintenance concerns at the design stage. Why make your own? DIY is Y i guess...maybe coupled with optimizing the coils for a specifically sized magnet...
SpeedRacerTerri (author)  seandogue8 years ago
Don't want to reinvent the wheel but personally I am purchasing/building a windmill and want to get the most for my $$. With an electric bill of $427 (Texas, coastal) this month the bigger the better seems to be key with me and will gladly heed good advice. Haven't figured out optimizing the coil yet... Thanks - Terri
kelseymh8 years ago
You can build it either way, but there are efficiency and simplicity issues.

First, there's the question of field strength. The current generated depends on the integral magnetic field (integral Bċ dl) cut by the coils. You need to know your field configuration with the magnets in the center, vs. inside a barrel of pole pieces, and go with whichever is larger.

Then there's weight and angular inertia. If the magnets are heavier than the coils, then you want them on the outside, so that you can maximize the rotation (and minimize frictional bearing losses), by spinning the lighter-weight coils.
If the coil assembly is heavier, then you can put it outside and spin the magnets. This also has the advantage (pointed out by Kiteman) that you don't need brushes or a slipring to get the current out of the spinning core.

Scavenging windings from an existing motor might be a good idea, but there are complications to consider. You're tying yourself to a particular geometry, for which you might not have a compatible magnet assembly. You're tying yourself to using a slipring if the coils are internal.
lol, I gave up on the idea of posting a decent mathematical formula a while back "(integral Bċ dl)" Your argument regarding moment of inertia makes a great deal of sense, considering that when the rotating coil/fixed magnet configuration was adopted, there was no such thing as a neodymium magnet...they needed to be much larger (and so, heavier) to get the same punch. I wonder though, if that might not be so much the case any more.
You wrote, "lol, I gave up on the idea of posting a decent mathematical formula a while back "(integral Bċ dl)""

Gack. You should see my own horrible attempt at posting real math. Never again.

I'm guessing you caught my LaTeX background as well in that mangled entity.
SpeedRacerTerri (author)  kelseymh8 years ago
nope, i was guessing the mh at the end of kelsey stood for motor home, which could be interrupted as trailer trash (just funning) my thoughts were more on the line of an RV, revealing my background. (smile)
Ding! give the man a gold star...

Yes. I posted a question today about the hidden formatting to asuage at least some of that...I'd like to be able to knowingly produce subscripts and whichever other special features I can, even if they're hidden within use of the punctuation marks.

In fact, on four occasions already I've avoided attempting to do the B = I... for that very reason...it'd be nice to access greeks too, but I think that might be asking too much... (I think I saw that someone used a deg marker as well...)

oh..wait...did you say LaTex? as in that's what's used here?
No, LaTeX is most assuredly not used here; more's the pity. It's just that I use LaTeX for all my work, and so stupidly I tried to use "cdot" as an entity name.

For the formatting stuff, take a look at our Instructable on the subject. You can get access to Greek etc. by using Unicode numeric entities.
Thanks Kelsey
SpeedRacerTerri (author)  seandogue8 years ago
Very true indeed. Of course I bought lots of NM that held 8 pounds each as they were available at hobby shop. Have enjoyed playing around with them but now understand I need much bigger ones!! Shouldn't be a poor investment tho considering my elect bill was over 400 last month at 11.5 kwh.