Alternator design, best motor advice e.t.c
hey you definitely seem to know a great deal about wind turbines and all of the math behind it. You were saying the dc motor i bought was good for educational purposes but not so much for usable energy. Luckily I am looking for the educational experience but would like to produce some "usable" energy, not to power a house or anything but at least a 12V battery. But in order to charge 12V battery i need to at least attain 12V output. From reading your post it seems i might be able to attain this but there would need to be a good wind and my blades should be between 2 -3 feet long each?
As I posted, you are working against two things:
1) Available Energy
2) RPM at a given wind speed.
Assuming a loaded TSR of 3, roughly 1m diameter blades should give you the RPM you need. There are numerous factors that are extremely difficult to predict in a system like this. Your TSR is actually a function of generator loading, blade design and wind speed and is all but impossible to calculate w/o some empirical data. As ghurd pointed out, the windings in your treadmill motor are designed to handle ~11 Amps, clamping your voltage to ~14V (charging a 12V battery) implies the max output will be ~150W. Honestly I would not consider 150W MAX output as being "usable power". Assuming storage and inverter losses combine to ~50% (a realistic figure) you would need one full hour of 150W charging to run your 1500W microwave for 3min. Put another way, if you made 150W for 24 hours, you could "save" 3.6kWh / 2 = 1.8kWh of energy; this represents ~$0.20 worth of electricity from the grid. If you live in an area with fairly constant 10m/s (23mph) winds, then the system you are contemplating could produce $72.27 worth of energy a year. (This assumes 10m/s 24-7-365.) If you live in an area with constant 5m/s (11mph) winds your "savings" would be roughly $9.03 per year. If you live in a more typical area with variable winds you will likely "save" considerably less than the $9.03. If you opt to "grid tie" your HAWT then you can multiply these numbers by 1.25.
With the above considerations in mind, I would consider a treadmill motor based windmill purely educational, providing no "usable energy". I mean no disrespect with this assessment, I think building a small scale HAWT to become familiar with them a viable educational pursuit, but it does not, IMHO offer any potential for "usable energy". If you have a remote cabin for weekend use that has no access to the grid, such an HAWT could provide useful LVL (low voltage lighting), or perhaps run a radio or other low power device, but it is unlikely to ever pay for itself in an environment where the grid is readily available.
My advice? If you want to learn about HAWTs, order a set of blades and set it up. Power some LED lighting in your garage/basement/workshop. Go into the experience with eyes wide-open looking to learn, not save money or power anything meaningful. I might even suggest that instead of buying a lead-acid deep cycle battery you consider purchasing a Lithium Ion cordless tool battery and a "12V charger" for it. This won't be any cheaper than a lead acid battery (likely more expensive), but this type of battery can handle deep discharge w/o damage, and you can avoid the entire charge controller expense. My goal is not to discourage you, but rather make certain you have a firm grasp on what to realistically expect from your system. All the ads make it sound like the world can be powered from the wind, and perhaps it can, but in the engineering world there are some very real obstacles to overcome to just power a DVD player.
In the future, it is best to keep these types of exchanges in-forum. In PM there is no chance anyone else will have a chance to read this response prior to asking the exact same questions. I do not mind helping, in fact I enjoy it, but the idea is to help everyone who wants to learn. To that end I try to do more than reply with, "No", "Yes", "Try 1m Blades"....I try to explain the math behind the answers so that others can make informed decisions for themselves.
Just for the record, everything I know about wind turbines is math and physics, I am still in the design phase of my first build. I am about 18 months into the design. My only goal is to pump 50% of my domestic water from a 45ft well into a cistern, and to add a "point-of-interest" to my landscape. You can reference my thread in the "Wind Power" portion of this forum. Ghurd and others have more "hands on" experience with HAWTs; but to date, nobody has "beaten the math"; it simply is what it is; I didn't come up with it, I just understand it.
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