6V vs. 12V System

[need bb]

I am installing a wind turbine at my campus in Rochester, NY which is going to power some wireless network gear.  I recently found out that the wireless gear has a wide input voltage from around 4.5v to 18v and draws around 10W.  I assumed to run the gear at 12v all along, but after doing some testing I am thinking of going to 6V.  My motor is similar to an Ametek but larger, and 12V cut in occurs around 300 RPMs.  I did some testing with my blades and it appears that cut in occurs around 15MPH and at this speed the shorted amperage was 3A.  The average wind speed year round is 10MPH, but during the winter 15-20MPH is common.  My blades work very well at low winds, so at 6V the battery would always be charging.  What are the benefits/negatives of using a 6V system instead of a 12V system?

Thanks

[scottsAI]

Hello need bb,

How does the current change with voltage?

Device may work with 4.5 to 18v, the best answer will depend on how and if the current changes with voltage. Dealing with power here, shooting to minimize it.

Storing extra power?

How long is the wire from source to load? (power losses in the wire)

Will there be other sources of power if the wind fails? (grid, solar...)

Please describe the whole system and your objectives! So we can best help you.

Have fun,

Scott.

[ghurd]

More infomation about the windmill would be helpful.

Sounds like 300 RPM at 15 MPH is slow for an Ametek type windmill.

Might be different blades would solve the problem.

G-

[need bb]

Well I will try to provide as much information as I can.  I don't know much about the motor since I found it (it is in great condition) and it has no information regarding it's performance.  From my testing it produces 12V at 300RPM and 45V at 1200RPM.  It is similar in size and performance to the Ametek 99, maybe just not as powerful.  The hub allows either a 3 or 2 blades and they are similar to the TLG Boatbuster blades:

http://www.tlgwindpower.com/rotors/boastbuster.htm

Some members have said that these blades are not that great for my type of motor.  I have tried a 2blade system which looks just like the new TLG Cyclone blades and it works a bit better than the 3 blades:

http://www.tlgwindpower.com/rotors/cy_clone.htm

The cable run is 15FT and is made from a thick extension cord.  I know it is not the best solution but it was cheap and it works.  I am not looking for 100% uptime for the wireless gear, since the project is just a demonstration and the wireless link isn't going to be carrying any important data.  The specs sheet shows that the input amplifier for the wireless gear is efficient in the 5-14V range, so the power (current changes similarly to voltage) shouldn't vary much from 10W if I run it at 6v or 12v.  My goal is for the most uptime as possible based on a constant 10W load.

Thanks

[ghurd]

There must be something wrong with the blades.

Maybe they are too long, or the outside areas are too wide?

I make some very seriously crappy blades, but I think they all would be faster than 300RPM at 15MPH.

Might try 3 of these PVC blades.  Like make 3 halves. 2' each is where I'd start, but I would expect to make several different lengths before I was happy.

http://www.fieldlines.com/story/2003/11/11/172721/53

The extension cord is not a problem.  Maybe later, but not yet.

G-

[need bb]

Well I was just estimating the 300RPM 15MPH since I didn't have an anemometer on me.  They might do 400RPM at 15MPH, but I am confident that they don't spin any faster in 15MPH.

[ghurd]

Could be there just isn't enough wind when you are watching.

Over-estimated wind speed was a big problem for me in the beginning.

Here, 15MPH is some Serious Wind at the levels I have to work with.  It's rare my anemometer reads above 8MPH, unless the forcast calls for over 20MPH.

Might be able to sign one out of the physics lab?

Call the local Radio Shacks, ask if they have part number 63-1119.  Probably sold them out 2 years ago, but worth a shot.

[need bb]

I really think that the wind a solid 15MPH since I was in between two building (creating a wind tunnel) and the local airport was reporting 20MPH winds.  Well I think I will try 4 thin PCV blades.

[snowcrow]

  Hi need bb, Adding more blades may help you start at a lower wind speed, but will cut your max. RPM's.  I would stick with 3 blades and play with they length and shape to get the desired RPM's.

Blessings, Snow Crow

[TheCasualTraveler]

     Back to 6 volts,

I would try to borrow a battery and simply test first to see that the network gear runs ok at 6v. Then I would measure what amps the mill puts out @ 6v. Definitly not going to give you lots of power but maybe fine for your limited application.

You said you did some testing, so what did you test and how did it go?