Crappy multimeter or what?

[wiley]

Mag diameter times 7. Using coils twice mag diameter. And works on 9 coil/12 pole PMAs (or 6/8 or 3/4). Gotcha.

That IS simple! Thanks.

But what about the hole of the coil? That still has me confused. You said your coil had a 5/16" hole while you used 1/2" mags? I thought the reason to use a hole at least the same size as the mag diameter was so that the same mag is never over both legs at the same time, which would cause cancellations. But with your 1/2" mag, it would always extend a little over both legs at the same time. But I take it that you found that it doesn't decrease output any/much otherwise you wouldn't be using it.  So yeah, if a smaller hole doesn't decrease output any/much than it makes sense to use smaller holes so you can get more turns or use larger wire. Ok, looksl ike I'll be making a new test coil 
Oh yeah, the reason I made a wedge shaped coil was because I read you want the direction of the mag to be perpendicular to the legs. Since you use round coils I guess that theory goes out the window too?

[ghurd]

Here's an example,

Ghurd's picture

Huge dimension pic, but only 60kb.

Huge dimension pics will no longer screw up the display width on some peoples displays?

I rarely had the problem before.  Sometimes.  Not often.
I did not know the old issue was fixed.

Fine job you are doing behind the scenes JW.
G-

[ghurd]

What Dan said.
Shorter blades go like heck.

By distance between the neos, I meant he air gap.
G-

[willib]

Mag diameter times 7. Using coils twice mag diameter. And works on 9 coil/12 pole PMAs (or 6/8 or 3/4). Gotcha.

That IS simple! Thanks.

Not so fast, you almost have it though.
for a 6 coil 8 pole machine the number turned out to be 5
and for a three coil 4 pole machine the number is 3.
i think you see a pattern here?
so if ya wanted to make an 18 coil 24 pole machine you would use 13.
on my sheet i go up to 15 though you could go higher , but making more than 21 coils was a mind numbing experience . i did it Twice with the 1/2 inch mags ,  lol
i had made two different sets of coils with two different wire gauges that went on a 7.5 inch diameter rotor with 28 poles and 21 coils .
If i had to do it again i would use a second rotor , cuz i only had one at the time .

[wiley]

By distance between the neos, I meant he air gap.

Oops, my bad.
I'm using a threaded rod for shaft, which is not ideal, there's a slight wobble. I just measured and the distance is 1/4" on one side and 5/16" on the other. No matter how I turn the nuts, I can't get the wobble out. Will have to use something else for shaft.


"Warning - while you were typing a new reply has been posted. You may wish to review your post."

Hehe, that's handy. Of all the boards I visit, I believe this is the only one that gives this warning.

@willib: Thanks for the correction. But yeah I see the pattern, so it's still simple 

[ghurd]

Oops, my bad.
I'm using a threaded rod for shaft, which is not ideal, there's a slight wobble. I just measured and the distance is 1/4" on one side and 5/16" on the other. No matter how I turn the nuts, I can't get the wobble out. Will have to use something else for shaft.

HA!
Same kind of problems I have!   

Except I don't follow those measurements and the pics.
Looks like 4 neos (2 on each disk), and they are 1/8" thick.
The distance from 2 on one disk to the 2 on the other disk should be less than 1/2", so I said 7/16".
You said 1/4", which sounds like a whole lot less than it looks like in the pics.

The magic number is all the magnets for that coil (4 x 1/8"), then go a little less.
9/16" is crap, but 7/16" is great.
(less than 7/16" does not help much in this type of PMA, within these parameters)

You might try all-thread couplings, or whatever they call them.  You know, those nuts that are an inch long.
The extra length should get rid of some wobble.

One nice thing about speaker plates is the tall section in the center, like the all-thread couplings.
Drill it a hair under thread specs and tap it, and it runs much truer than flat disks between nuts.
Most speaker plates are manufactured to decent run out tolerances, though I can not imagine why.

[wiley]

You said 1/4", which sounds like a whole lot less than it looks like in the pics.

I said 1/4" and 5/16". I guess what you're seeing in the picture is the 5/16" side 

less than 7/16" does not help much in this type of PMA

Huh? I thought the smaller the airgap the better. Oh well.
If I reduce the airgap to 7/16" it will reduce output. But at the same time I can use thicker coils and get the same turns with thicker wire, reducing resistance. Hey maybe the resistance was the problem for the small output all along? I'm using #30 wire.

I'll go see if I have some all thread couplings 

[wiley]

In the pictures below, the coil on the left was also in the picture on page two. Haven't mentioned it before.
It's about 5/32" thick, has 50 turns of 22 awg wire and it produced .8V at 800 RPMs.
The airgap was 1/4" on one side and 5/6" on the other (big wobble )

Why am I mentioning this now?

Well I made a new test coil, a round one. It has 97 turns of 22 awg wire (was going for 100 but ran out of wire ) I decreased the coil's hole diameter to 3/8". In the second pic you can see how much smaller it is. It's about 1/4" thick. I increased the airgap to 3/8", give or take 1/32" (slight wobble).
Output? A measly 1 volt at 800 RPMs 

So.... was it the increased airgap that did it? Or the coil's smaller hole diameter?

Dunno! Will keep testing 

[ghurd]

"The airgap was 1/4" on one side and 5/6" on the other"
Uh... Nope?

The air gap is from the magnet face to the magnet face.
It includes the space on both sides of the coil, and the coil.

If there was 1/4" on one side, 5/16" on the other side, and 1/4" of copper coil, then the air gap was 0.8125"?
And that should be a tad less than 0.500".
That's probably why the voltage is low.

Smaller makes the flux stronger, but leaves no space for fat low-resistance wire.
High flux and high resistance makes for voltage that can not make amps into the battery.

Grab old TVs and computer monitors on garbage night.
(the 3 weeks after Christmas is like a gold mine... if my wife would let me do it anymore)
Degaussing coils are made of maybe #21~24 magnet wire, and a really long piece of it.

Those coils look nice.
G-

[willib]

Did you bring in the diameter of the magnets to 3.5 inches?
what is the outer diameter of the new coil?
cant tell from the picture, but it looks less than 1 inch
both those things will greatly effect the output .

[wiley]

The air gap is from the magnet face to the magnet face.
It includes the space on both sides of the coil, and the coil.

Yes, and that's what I measured. And it was 1/4" on one side and 5/16" on the other because of the wobble.

If there was 1/4" on one side, 5/16" on the other side, and 1/4" of copper coil, then the air gap was 0.8125"?

No, I used the thinner wedge shaped coil with that air gap. The new 1/4" thick round coil I used with a 3/8" air gap (well give or take 1/32" there was a very slight wobble in there).

@willib: its actually about 1". The right leg is covering the 8 in the picture 
I didn't bring the mags together yet. I don't wanna change too many variables at once. It's complicated enough

[willib]

after you correct the magnet spacing ,
if you have a diode handy check the voltage with the meter ON the DC scale.

If you dont have one handy , there has to be a device around the house that has one in it. ( something not working of course)

see if you can unsolder one or clip the terminals as far from the diode as possible , just to give you enough room to solder it to your coil.

ohh you may have to clean the ends of the wire before soldering , that enamel coating will come off with a lighter and some fine sandpaper.

just heat it up till red , let cool , and sand it clean.

[wiley]

Willib, I was making a new video while you made that post. I still haven't corrected the magnet spacing. But now I'm not sure if I can, because I made a new coil and I'm thinking of making 8 more of these. My new test coil has 100 turns of 26 awg wire. It's 1/8" thick, has an inner diameter of 7/16" BUT an outer diameter of 1-1/16". This means, if I reduce the magnet spacing to 3.5" then the coils won't fit anymore. I mean they had to be 1 inch right, no room for 1/16" more? I don't think I can squeeze the coils together to make them fit without damaging them. I use super glue and they come out hard but brittle, if I squeeze them I'm pretty sure I'll break the brittle glue and possibly the wire as well.

I found an all thread coupling and it reduced the wobble. I reduced the wobble even more since I did the video and there's so little wobble now that I don't even wanna touch it again 
Because of the less wobble I managed to increase the output of the thin wedge shaped coil by 0.1 volt. From 0.8V to 0.9V.

Video: http://www.youtube.com/watch?v=i3QR3UPMvkk

[willib]

wiley magnet spacing and  coil diameter is super critical to the proper working of an alternator.

nice video . i cant see the rotors spinning

the way the magnetic flux sees the coil has to be the most important aspect of a good working alternator. If the magnets are too far apart , then as a north is leaving the center of the coil , the south pole will get there too late to do much good.

and its the north and south poles hitting the coil at the same time that produces the most voltage

if you haven't glued the magnets down yet , do yourself a favor and try it.

[wooferhound]

Another thing is that those meters are most accurate at an AC frequency of 60 hz

[wiley]

Willib, I corrected the magnet spacing. It actually reduced the voltage 

http://www.youtube.com/watch?v=6ZXsyxMK8C4

[willib]

good going !
almost two volts
not too shabby..

[ghurd]

This is so long I am confused.

How many turns in the green coil?

It looks like you removed a layer of magnets from one disk?
If that is how the air gap was increased, then it has 3/8" of neo and 3/8" of air gap?  Usually best, I think, to try to have the air gap a bit less than the neo.  With 3/8" of neo, a slight change from a hair over 3/8" to a hair under makes a big difference.  I have the same mechanical difficulties as you, and my perspective may be skewed.

G-

[wiley]

This is so long I am confused.

How many turns in the green coil?

It looks like you removed a layer of magnets from one disk?
If that is how the air gap was increased, then it has 3/8" of neo and 3/8" of air gap?  Usually best, I think, to try to have the air gap a bit less than the neo.  With 3/8" of neo, a slight change from a hair over 3/8" to a hair under makes a big difference.  I have the same mechanical difficulties as you, and my perspective may be skewed.

G-

I've done a lot of testing lately, I'm having trouble keeping track of what I've done myself 

There are 100 turns of 26 awg wire in the green coil. Air gap is 1/4". I have two 1/8" thick mags stacked on each rotor, so there's 2 north poles on one rotor and 2 south poles on the other, so there's 1/2" of neo.

I remember one of your earlier posts where you mentioned that with 1/2" of neo that an air gap of 7/16" was about right and that further reducing of the air gap wouldn't do much good. But with all that testing, I found the smaller the air gap the higher the voltage.

[ghurd]

The smaller air gap will increase voltage
BUT... the increase from 1/2" to 3/8" is a lot less than from 5/8" to 1/2", so there is not a lot of gain,
and the space for heavier wire gets reduced a Lot.

Do not fall into the trap of chasing voltage.
It is easy to get lots of voltage with tiny wire, but the tiny wire will not let the power get out of the coils and to the battery.

Get the air gap right, find out how many turns needed per coil, then use the biggest wire that will fit in the air gap with the number of turns.
G-

[wiley]

The smaller air gap will increase voltage
BUT... the increase from 1/2" to 3/8" is a lot less than from 5/8" to 1/2", so there is not a lot of gain,
and the space for heavier wire gets reduced a Lot.

Do not fall into the trap of chasing voltage.
It is easy to get lots of voltage with tiny wire, but the tiny wire will not let the power get out of the coils and to the battery.

Get the air gap right, find out how many turns needed per coil, then use the biggest wire that will fit in the air gap with the number of turns.
G-

Crap, I think I DID fall in that trap 
I'll do some more testing with bigger air gaps. I already made a 1/4" thick coil with 100 turns of 22 awg wire for an earlier test. I'll increase air gap and see how much voltage I'll get this time and then calculate how many more, if any, turns I need for cut in.

One more thing.. (I would appreciate it if someone could answer this for me because I can't seem to find it on my own)

Do I need 1.9V per coil or 1.6V?
1.9V is when you wind for 14V and 1.6 is when you wind for 12V. A battery is full at 14V, so it makes sense to me to wind for 14V. Or am I missing something?

[ghurd]

"so it makes sense to me to wind for 14V"
Me too.

One more thing I didn't see mentioned.
The rectifiers will use up about 1.4V.

With the drill spinning slower than rated like they do, I expect it will more than make up for the diode loss.

The voltage trap is only one trap.
Aiming for too low a cut in RPM is another trap, though the 2 are very closely related, and have a cousin called low wind power.  In fact, those 2 and aiming for low wind power is the trifecta of newbie mistakes.
I chased the trifecta for years.  It doesn't work.
G-

[wiley]

Didn't have enough thicker wire, so I went ahead and made 8 more of those thin green coils. (100 turns, 26 awg wire)

Casting the stator was a disaster, it's ugly but at least it seems to work fine.
The stator is about 3/16" thick. Because of the slight wobble I had to increase my air gap from 1/4" to 5/16". Oh well.

I got 12.8V at 800 RPMs (or however fast that dang drill spins  )

I connected the positive wire from the rectifier to the red lead of the multimeter and then from the black lead of the multimeter to the + on the drill you see in the picture to measure current. I got 2.1 amps with the drill at full speed, which I'm sure is less than 800 RPMs with a load.

Anyways, 2 * 12 = 24 watts. Bad? Good? In between?

[ghurd]

I can't really see what is going on there.
Looks like one single 1-phase bridge?
9 coil-12 pole?
It is wired Wye or Star, right?
G-

[wiley]

Sorry, its wired star.
9 coil 12 pole, correct.
And there are two full wave bridge rectifiers rated for 4 amps and 50 volts. I glued them to each other, that's why you probably thought it was one. I know I'm suppose to put hem on heat sinks, but I don't need it to last forever. This is my first PMA, I'm just building it to see if I can do it and to get experience, etc. I'll probably make many more before I go on to the bigger stuff.