Various assorted questions and one OT question

[ADMIN]

I'm working on our Homebrew Wind book with DanB, pretty much full time right now. So the only section of the board I'm monitoring regularly is "Newbies" here. Great info from everyone to answer all these questions! Here's my crack at it, everyone feel free to rip apart my answers for errors -- there will be some. But it's a fun series of questions, and the results already (before my input) are vying for an FAQ--every one of these questions is asking about really important concepts. So, it's nearly midnight and I'll give it a shot!

1. - the more power your alternator is trying to harvest, the harder it is to spin. Watts are watts, no matter if it's electricity or dogs running. Short the alternator out to get max power output, and it'll be very difficult to spin by hand, a human could never get it going. Hook up a 10 watt light bulb, and you'll need to put in about 40 watts of WIND power to light it up....hook up a 100 watt bulb and you'll need 400 watts. Watts can be used to measure any kind of power, which is energy over time...you can measure the energy it takes to lift a rock over your head in watts. A small wind turbine can be expected to capture at MOST 25% of what's available, averaged out.
   
2. - With what we build at otherpower.com, the part that turns the power the spinning blades have harvested from the wind into electricity is called an alternator. Called such because it makes alternating current (AC) instead of direct current (DC).
   
3. - I am overworked and need a raise, that's why the glossary is not complete. The one in our new book will hopefully cover the missing areas.
   
4. -- actually the wind turbine makes 3-phase AC at a frequency that varies with the wind speed. This makes it nearly useless for runnning any of your gadgets. We convert it to DC with rectifiers so we can charge batteries with it. Then, if we have an inverter, we convert it to 120 volt single phase AC like that in a typical townie wall socket. TYou can use it right from the batteries, too -- DC
   
5. -- The voltage is what's most important, not AC vs DC --  the higher voltage of normal 'house current' AC is what makes the difference..120 volts vs the standard 12 volt battery can travel much farther on the same size wire with less loss. The really big issue though is that you can buy AC light bulbs, stereos, TVs, toaster ovens, fridges, computers, and such that run on 120 volts AC at Wal Mart. Anything that runs on DC will be exotic, hard to find, and expensive.
   
6. -- when the wind speed doubles, the power in it increases by a factor of 8...it's exponential! If your wind turbine alternator can't take out this huge increase in  power,or reduce the input by furling, the extra power goes to increasing blade speeds and making heat in the alternator....it turns your alternator coils into an electric toaster. But you can't put the toast in there without climbing the tower....
   
7. -- This is difficult to generalize. But, the more mass of magnets you have in there, the more power you can take out of the wind and harvest. BUT, the slower you need everything turning (low RPMs) the more magnets you need, and the heavier and more expensive the machine. Better to use lift forces from the blades airfoils to increase your RPM, as energy goes up with the square of blade velocity. Machines that dont use lift forces from airfoils don't make much power, beacuse they don't spin very fast compared to how fast the wind is blowing. In most machines that we build, the blade tips are moving about 6 times faster than the wind is blowing.
   
8. - Naw. Instead go to:
   
   

http://amasci.com/elect/vwatt1.html

Best electricity explanation I've ever seen, much of it is going into our book where we try to explain electricity....and if you can ever catch one of this guy's electricity demos, do it! Bill Beatty really explains it well here I think.

9 - We have lots of dogs here. Don't know about dog cart design, but the lesson in work vs power is a good one----Energy (work) is how how hard you have to push something. Power measures that, plus for how long you push it. Power is measured in watts. My big old porky elderly husky dog wrote a haiku to explain it (it'll be in our book):

Volts, ohms, amps and watts

Dog power is measured in

Kibbles per hour

Cheers -- ADMIN

[finnsawyer]

Well, I think you guys better read the book again.  Your statements under one are not true.  A linear alternator or voltage source does not put out maximum power when the output is shorted.  In fact it puts out zero power.  If there is no resistance there is no power no matter what the current.  It will still take power to turn the alternator due to the finite resistance of the coils that make up the alternator.  While this is the maximum power that it takes to turn the alternator at that RPM, it is a result of simple circuit analysis that maximum power to the load will occur when the load resistance matches the alternator resistance.  Your statement that it takes 4 times as much power into the alternator as you get out would only be true if the alternator resistance is four times that of the load.  Hopefully, that is not the case.  In general one would like the resistance of the alternator to be substantially less than the load, in which case most of the power it takes to turn the alternator would end up going to the load.