Kind of a summary of what I learned from this project;
When you build a single phase generator for battery charging it's best to use a different "factor" when figuring the number of turns in the coils, derived by running a test coil. With three phase, if you get 3.6 volts from a test coil with a 9 coil stator in wye, you'll get your rectified 25 DC volts at the right cut-in speed. With single phase it doesn't seem to work that way because the diodes are only conducting when the AC sine voltage is above battery voltage. So I kind of developed a new "rule of thumb" that you use a 1.25 factor instead of 1.414 if you want the cut-in speed to be right.
For instance, on this 10 pole I figured I needed 1.9 volts AC from a test coil. That should give me 19.0 volts with 10 coils, or 25.5 volts rectified to DC. It does....... BUT.........the cut-in is "soft" and not as distinct. I'm playing with building a single phase 12 pole with neo magnets so I can compare performance between the neo and ferrite magnets. I found sort of the same thing with single phase even using neos. The three phase will start pushing that first amp against a battery bank at 25.5 volts when the AC voltmeter shows around 19 volts. With the single phase it doesn't seem to start moving that first amp of current until it gets to 21 volts AC.
As Hugh explained, the single phase generator delivers power in pulses, probably not unlike a PWM solar voltage controller. The current only flows when the sine voltage is high enough to exceed battery voltage. Then when the sine wave drops below that point the generator is unloaded and spins free. As I've come to find out this is NOT bad. The turbine doesn't stall with it as quick, and doing some testing this afternoon on my single phase neo project, I found this is more of a characteristic of single phase rather than the weak ferrite magnets. The generator is not as "stiff" with single phase neo as it is with three phase, using the same magnets, same air gap, just different stators - one three phase, the other single phase. That was kind of a neat thing to learn.
With single phase a flat topped sine wave probably works the best. This means paying attention to the hole size in the coil. The hole should be at least as big as the magnet so once the coil is excited and the sine wave above battery voltage, it stays there awhile. This should make the single phase generator more "stiff", but it will also probably increase the vibration from loading/unloading of the generator rotors because it will be more abrupt.
I think what I stumbled upon with this 50 turn single phase shown in this thread seems to work pretty good. It runs smooth, it delivers excellent low to midrange power, but it's short on top end power compared to a neo three phase even with the rotor running much faster. Oz asked about "limiting" early in this thread. And I think Oz knew more about it than I do. It does indeed "limit" because it's inherently less efficient than a neo three-phase. And the turbine furls fine with it that way - just at less power output than with the three phase. The only thing I changed in the furling was to turn the power up a bit (make it furl later) to try to get more out of it in high winds. Even that didn't make a hell of a lot of difference.
I think the faster you turn it the more power it will make, but the blades will only go so fast, and if they're loaded at all by the generator the machine furls. In other words it's a pretty "safe" turbine. I really think burning it up would be quite hard - you'd probably have to lock the tail sold and just let it scream in a thunderstorm to burn it up. I was concerned, at first, because it's only wound with 13 AWG wire, that it would be too light duty for a 12 foot turbine. That doesn't seem to be the case because it won't deliver over 40 amps sustained. I seen it up to 1800 watts once, very briefly, but it wouldn't stay there like the three phase neo generator does. The turbine furled and it dropped back to about 35 amps and then never went over 40 again. Meanwhile the other turbine with the three phase delta generator with neo magnets was running at 60-70 amps sustained during that same thunderstorm, when I got the 1800 watt spike out of this single phase unit.
So yes, Oz, I have arrived at the conclusion that it does, after all, self-limit simply because it's weak compared to the neo gen. If you live for and hold your breath waiting for those big power spikes from your turbine in storms, you'll probably pass out before you ever get it from this single phase unit.
I thought about what I would do different on this one if I were to rebuilt it, and I decided nothing, basically. It works good. The only thing would be to lower the cut-in a bit. Somebody else asked about air gap so I decided, sure, why not? I had the air gap at .775" and I got lots of room to play with it. So I lowered the tower this evening and removed .075" of shims from the generator to see what that does. I realized I had never taken a photo of this generator all assembled, so I took one tonight:
Some folks are going to see the "claws" on the rotors. I tested that, both with and without those "claws" and they didn't make even 1/100th of a volt difference on the test coil. I even put some brake lathe shavings on a piece of plexiglass and held it over two rotors, one without the "claws", and the other one with them. The only thing I could see that they do is that the flux lines that appeared to be extending outside the generator pole, to outside the perimeter of the rotor, were sort of "squeezed in" by the claws so the flux lines are more concentrated over the winding head on the coils instead of whirling around in outer space. So I welded them babies on there. Those big magnets weigh about 3/4 lb each. If one came zingin' off there when the generator is turning at 1,000 rpm and bonked you in the knob you probably wouldn't survive to tell your grandkids about it.
So that's all the stuff I learned from this project. It was pretty cool. I got a whole collection of these magnets for less than 100 bucks. So I'm going to build some more of them, just because it's so fun. The turbine flat out HAULS with this single phase ferrite magnet generator, which makes watching it run a lot more fun.
--
Chris
