.... .. Talking Trash .... .. A trash stator that is!
Here is a very common sight these days in our throw away society:
Just a few screws and some cutters yields some very nice magnet wire:
sometimes several hundred feet in a TV or CRT computer monitor:
In our first post we found that we can obtain an AC voltage in our test coil of 3.51VAC with 135 turns at a speed of 500 RPM.
Lets see what a star connected stator might do at that speed: ?
3.51VAC X 2(coils in series)= 7.02VAC
7.02 X 1.73(star connected)=12.14VAC
12.14 X 1.4(AC RMS to rectified DC)= 17.0VDC
17 VDC - 1.4VDC (rectifier voltage drop)=15.6VDC @500RPM
How about 400RPM?
500RPM X 0.8=400RPM
15.6VDC X 0.8=12.48VDC not too bad!
I feel that might still be a tad high for a lowish battery at 400RPM and decided to back it down another 10%
135 turns - 10%=121 turns per coil. (went with 120 turns
) for what it's worth I would guess that our flux density is just under 400mT..compared to the big machines running about 700mT.
We collected a good supply of AWG#22 wire..#21 might have worked out a little better if i had it.
GoVertical has some eagle eyes and asked this:
Hi, why did you choose to make the coil ID smaller than the magnet OD?
The short answer is->because we found that we could. with some testing we found that we can squeeze the ID down a few percent (12.5% in this case) and still get the same induced voltage. We went this route for several reasons.
1) we are able to get a bit more wiggle room for possible errors (sloppy windings etc) and still fit the coils in the allotted space.
2) 1/8" smaller diameter coils gives us a bit more room (about 1/4") in the center of the stator.
3) allows us to use less wire for the same number of turns and voltage (a total of 252 feet as opposed to 312 feet)
4) a stator with 20% less wire has 20% less resistance.
5) the little plastic spacers that came with the magnets are 7/8" diameter and made for a nice center for the coil winder we worked up for the task
For the stator we went with a non casting method..just glued the coils down with a total of 3 ounces (6 tablespoons) of resin.
our stator mount to be:
we cleared a salvaged 0.060" PCB board with a dremel and attacked it with a belt sander..ended up
0.050" thick with lots of thru hole traces still on it some small bits of copper plating as well..I do not believe these small traces of conductor will be an issue, Anyone think otherwise?
we notched out some grooves for the coil starts 0.030" deep.
a little loose with the spacing..#21 or a half size between 21 and AWG 22 would have been better.
these coils are 42 feet each of #22..120 turns about 0.7 ohms.
Looks like a fun project. I would try using larger rotor discs,and winding thinner coils.7inch saw blades are pretty easy to find. and will give more winding room.
agree with you 100% jlt. maybe next time around with different disk mounting techniques and adjustable airgap..this fixed airgap spacer is a keystone to this build<- more happening with the spacer than it might first appear.
thanks for having a look, to be continued..out of room in this post for now.
It's all good fun!
dave