Just a few more updates on My LenzII. Everything is complete and it's ready to go up in the wind. But before I do that, I wanted to benchmark the alternator.
This is my 2nd alternator. The first didn't meet my expectations in regards to craftsmanship. The first was based on an 8" rotor disk with 12 of Ed's wedge mags. I really struggled to get the 9 coils fitted in place. Those coils were 65 turns of 2x 18ga. After a disasterous potting process, I took waht I learned and tried again.
The new alternator was built on larger 9" rotor disks, and I bumped the turns to 70 per coil, and they were wound with 8 strands of 24 ga instead of 2 strands of 18 ga.
Just for fun, I compared coils, both 70 turns, one with 2x 18 ga and the other with 8x 24 ga. (see below)
They came out nearly identical in size, but the biggest diefference was that the 8X 24 ga is very soft and flexible.
Even with the softer coils, and moving up to a 9" rotor disk, I still had troubles getting all 9 of them packed into the magnets circle. Before winding the coils, I used a test coil to set the pin spacing on my Lenz coil winder. I wound the coil, then checked it's fit into a gauge, unwound it, adjusted the winder, rewound, rechecked..and so on. After a few iterations, I felt like everything was going to fit nicely. Which it did for the most part.
I cobbled up an assembly fixture which gave me an extra set of hands for taping the coils together:
One issue that I wanted to resolve on this stator was to get rid of the loose wires dangling out of the casting. As Murphy would have it, they are just asking to be damaged and rendering the stator useless. So, I made some stator "terminal buttons" which were cast with the coils in polyester resin.
The buttons were turned out of brass, knurled, drilled and tapped with 10-24 threads.
Then they were soldered onto the output legs of the coils:
Once everything was set in the mold, the buttons were bolted in place through the bottom and the assembly was potted with polyester resin.
This was my second casting attempt. It's gets easier with experience!! A lesson learned on my first attaempt was to mix up more resin than you think you'll need. Resin is cheap compared to the time and money spent up to that point...so don't run out when you start to pour...because it's impractical to mix more in the middle of the process. Don't Skimp on the resin!!!! It's OK to throw out the surplus.
I was very pleased when I opened the mold and saw the results.
The terminal buttons came out beautifully!!
Another thing that I did on this attempt was that I printed a lable that was potted with the coils. The lable reads: "70 turns, 8x 24ga. 06/24/09".
You can faintly see it in the photo above.
Now I can read the details on this stator in the future when I've forgotten everything.
Next, I mounted the alternator in a milling machine with the rotors being driven by the milling machine spindle. This machine has a variable speed drive and I can adjust the rpms on the fly from about 70-3000rpm.
I measured the DC voltage from the rectifier and plotted it against the Rotor speed in RPMs for my 2 different alternators.
The 65 turn alternator is in blue and the 70 turn is in red. The blue (65t) reached 12V at 85 rpm and the red (70t) reached 12V at 75 rpm. So, I think I'll start charging at slower speeds. I think this is good...and will allow me use a larger range of wind speed with a MPPT controller.
Other than making electricity, I really don't know what to test. Being mounted in the milling machine, I can drive it at a constant rpm regardless of the electrical load...and in any speed from about 70-3000 rpm. However, 300 rpm seems plenty fast.
Is there anything you guys would like to see on the test stand before I put it on the Lenz and into the wind?
Well, that's where I'm at today. I think I'm going to wait until the weekend to hoist everything up on the tower.
-Rob
