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25 to 30 foot diameter turbine
Janne:
oztules,
Thanks for the lenghty writeup. I'll have to study it in more detail, it's a bit much to chew on one readup :)
methanolcat:
thanks oztules,
That is a lot to chew and fully understand but it does help to give a better grasp. I can't go grid connect with a 3 phase motor cause we don't have 3 phase out here, or I would consider it. Now to do that with a single phase motor, I don't know of any big enough, seems your bigger motors are all 3 phase, plus theres a limit on how much I can put back into the grid here, and to keep this from getting too long, in basic terms grid tie is a rip off, at least around here.
I do have a huge battery bank on its way later this summer, possibly fall before I see it. I also plan to use some of the power for my water heater. I get the most wind in the fall and winter, actually when I need the most power in terms of heating the house. I heat with corn, always 200 bushel to make it through the winter, this last winter I took a chance and only bought 100 bushel and luckily since last winter was my first with a turbine flying we did just fine, it made up for the other 100 bushel.
On the corn issue, when I bought the stove, corn was the cheapest form of heat at $2 a bushel, I could heat my house for $400 for one winter. 8 years later, corn is now $7 a bushel, thanks to the ethanol plant that moved in 4 miles from me. So I am trying to get away from corn as much as possible, the only other alternative here for me is electric heat.
Not too sure where I'm going yet with the generator but I am going to continue on with the gear box as I can pretty much hook up any generator I decide to use. Heres a few pictures of where I am with the gear box. The last picture has a can of Pepsi in it to show the size of this thing and the bearings I am going to use.
flange thickness is 3/8", rolled steel ring is 1/2".
drilling holes on mill
top and bottom plate are both 1/2" thick, tube is 4" I.D. 3/8" wall thickness
last picture showing scale of gear box and front bearing and some 3/8" plate to make gussets from.
Matt
SparWeb:
Methanolcat!
Where to begin?!
Definitely be concerned about reactance limiting in a motor conversion.
If you haven't followed my projects, I'm on my 3rd motor conversion. I've done a 7.5 HP, too, but it has yet to fly (like yours).
I'm currently using the 3HP Baldor conversion, and I can easily measure the reactance limiting the output.
Here's what it looks like on mine:
That is NOT furling. That is the inability of the current output to increase, despite ever increasing speed and increasing open-circuit voltage. The current is flowing through the windings, so every tooth of the stator is now a tiny electromagnet pointed backward at every one of the magnets. They come into balance at some point depending upon the current density per turn (or something like that). This one is wired in "Jerry", meaning each phase is rectified separately, and in Star, the reactance is even worse and the thing is limited to 600 Watts output.
This is all smaller scale than your project, but I think the lessons are directly applicable. I don't know if I'm the self-appointed expert on motor conversions but I'll try to answer what I can from the experience that I have. I spun up my 7.5 conversion, and the 3hp, on a lathe to measure power in & out.
From those tests I estimate that a 15-16 foot prop will be plenty for my 7.5 hp conversion, when I get around to it. As it is, I think it's a good match for direct-drive at 48 volts, at that blade size. Not so good for my current 24V system, so yet another reason I can't use it right away.
I have a few thoughts about the gearbox and feathering prop, too. Not so much critique as doubt that it will come in under 250 pounds (your genny weighs over 100 already) or that it will be low-maintenance. You are extremely talented and resourceful, that is not what I'm questioning. It's the thought of spinning the genny 6x faster, which uses up the bearings 6x sooner. Admittedly the gearbox takes the rotor loads instead of the genny shaft, but you still aren't scott-free.
SparWeb:
Uh that's not legible. Try this:
methanolcat:
SparWeb,
Your right, my generator by itself weighs around 100 pounds, actually closer to 80 pounds (mine has the thick sheet metal case instead of more common full iron cases). I'm not trying to save on weight, I want strong and I actually said "I have started on the gearbox and I think JUST the gearbox is gonna weigh in around 250 pounds." No big deal.
I'm estimating the feathering hub to weigh about 75 lbs +, blades about 40 lbs each, generator 80 lbs, gearbox 250lbs and swivel mount 40-50 lbs. That all comes to about 570 lbs. Not a problem, throw in a tail and were over 600 lbs.
I'll find out all about what reactance limiting is when I run some tests, I'm gonna wire a 20 kw load on the generator and run some tests at work and see what we can get out of it. I'm gonna hook up a thermocouple in the winding to monitor temperature. I'll do testing at several rpm's and that should help figure out a gear ratio to use, if I can even use this generator.
What was you able to to get out of your 7.5 as far as power, or do you know?
Your estimation of 15 to 16 foot prop is close, mine is 15 foot and I bet I could cut it down to 14 foot and not notice much if any difference, maybe faster but mine gets too fast now.
Matt
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