I have been lurking here for a short while and was determined not to ask any stupid questions as all the answers are already here. But now my head just hurts. Sorry . . I tried really, really hard!
I live in the UK and have a remote off-grid property in Northern Spain. I am building my project in the UK for use in Spain. Unfortunately, I have little experience of the prevailing wind conditions at the deployment site.
My existing system comprises two 6 V 560 Ah lead acid batteries connected in series into a 1000 W 240 V inverter which I charge using the 50 A alternator fitted to my car. My electrical demands are small - one 11 W bulb and a 60 W TV or lower power radio a few hours most days. I have an 850 W microwave but used it only once before realizing it is too power hungry. In practice I fire the car up for half an hour or so every few days and then I'm good to go. I suspect I am using no more than 500 WH per day.
I have built many virtual wind generators, the 7 ft and 10 ft Volvo hub based otherpower designs and I even put together an imaginary 10 ft mill using the current "No Volvos were Hurt in the Making of this Machine" design. Before I pick up a real piece of metal though I decided I better get something - anything - working in the real world, hence the acquisition of the Reebok RT1000 Treadmill motor I just bought:
Specifications: 2.25 HP Continuous duty at 230 Vdc, 9.5 A. Speed is not specified so I powered the motor with a 9 Vdc supply and observed rotation speed of 210 rpm - 23 rpm per Volt. Approx 5366 rpm at rated supply voltage. A search on google turned up other motors for this same treadmill rated at a different voltage but at 6000 rpm. I therefore assume my motor is a 6000 rpm device, requiring 26 rpm per Volt.
I -think- my two 6 V batteries will start charging at 6.5 V (150 rpm) or 13 V (300 rpm) depending on configuration. Series connection would be inconvenient but possible (I would need two sets of batteries and would have to disconnect and reconfigure them regularly).
I also think I understand that in any given wind using any design of blades where cutin speed is exceeded the higher voltage battery load will receive more power than the other. I do not fully understand this mechanism though.
I came in here with a question ... I'm sure . . . oh yes. Blades ... given that I am not sure about the wind my rotor may see what might be a first try on PVC blade design to best guarantee charging my 12 V battery bank with 3.5 kWH per week, assuming a cut in speed of 300 rpm? I have see three different pvc designs on these pages - one is a 2-blade design cut from a single length of pipe, one comprises 3 or 5 blades with a simple profile resembling a wood saw and a third aesthetically brilliant design (http://www.otherpower.com/images/scimages/6863/PVC_blades.jpg) has a sweeping bulge near the root - this resembles the shape of the huge commercial rotors I see. Which might suit my purpose?
I have also seen diffent PVC pipe diameters mentioned. To make a blade of a given width "W" I could use a pipe with a diameter as small as "W" (a semi-circular profile) or any larger diameter, giving a shallower attack. What is best? Some seem to be 90 degrees, allowing the cutting of four blades from a single pipe. What would be the effect of cutting three blades of 120 degrees from a pipe? What does that pretty bulge do for the blade?
Thanks in Advance.
Mal