wind powered night lights

[Eufouria]

Also, you'll have to get at the PCB inside to (disconnect the commutating electronics and) connect a rectifier. .

Why would I need a rectifier? Wouldn't the fan be putting out DC?

I think I will skip all commutating for simplicity and efficiencies sake.

 

[Resqueline]

Children sometimes speak into your mouth because they believe where the words come out they must also go in..
A computer fan as I stated is an internally electronically commutated stepper motor, and as such it is essentially an AC motor and doesn't put out DC - even if it runs on DC, which is why I stated it needs a rectifier. Only permanent magnet brushed motors puts out DC, and even they need a diode in series to keep it from running off the battery.
The reason I suggested disconnecting the drive electronics is that I was thinking it might steal some of the current when used as a generator but then again it might not.

 

[Eufouria]

Hey guys, just got my crate of computer fans from NJ and during some initial research I came across this very detailed site:

http://www.otherpower.com/toymill.html

It states that brushless computer fans won't work, is that simple because she isn't going into the process of adding a rectifier?

Also here is a picture of the circuit board from one of the computer fans, it looks as though it will be difficult to bypass. Am i correct in guessing their is something on the board that keeps the motor from acting as a generator? Would there be a way to bypass that?

 

[Resqueline]

He states they are brushless and won't work, yet he converts brushless VCR motors which works on the same principle..
I don't see any reason it wouldn't work, but in some fans it's just plain hard to gain access to the board w/o destroying it.

 

[Eufouria]

Hey guys, midterms had me booked for the past month but I'm hoping to move forward a bit during spring break.

I was talking to a friend at NYC Resistor (a hacker space) last night and he warned me of the voltage drop of diodes, which if I am planning on using in series to prevent the fans from powering each other before reaching the battery could be a substantial loss. Can anyone suggest an alternative method or an efficient diode for me to look into?

 

[Mitchekj]

A Schottky diode normally has a "low" Vf (drop). 0.3V-0.5V is fairly common. I haven't read all of your application, so I'm not certain how much of a drop would be acceptable here.

 

[Eufouria]

Hm, that will be problematic, are there diodes with a lower drop voltage?

The only hope I have of producing even 5 volts is by running a bunch of my computer fans in series each with rectifiers.

I think I'm going to have to resort to finding better generators.

 

[Mitchekj]

I'm not aware of anything with a lower drop, if there is such a thing in existance: it's going to cost $$$

 

[55pilot]

Actually, you can have "active diodes" that can get the voltage drop to well under 0.1V. They are actually a MOSFET and a controller. The MOSFET is installed "backwards" so that the body diode is forward conducting. The controller detects the voltage drop across the drain and source and drives the gate to servo the voltage at the target voltage. Linear Tech makes the controllers for this, as do others. It is usually used for power management where you are dealing with several to several 10's of amps.

I have not read through this whole thread, to know if it is applicable here, but they do exist.

---55p

 

[Mitchekj]

Ah, brilliant. I need to read up on those.

 

[55pilot]

Ah, brilliant. I need to read up on those.

Linear Tech calls them "Ideal Diode" controllers. LTC4357 is one of the two dozen chips in this family. The LTC4357 servos the MOSFET to limit the drop to 25mV. Using real life MOSFETs, for a load current of 10A you can get the power loss down to under 0.5W, as opposed to 6+W for a Schottky diode.

---55p

 

[Eufouria]

Hi all, been a while.

I've finally procured a DC permanent magnet motor from an old treadmill.

However (of course) it is not perfect, it has some odd rating which I am unsure of:
Electrical Rating @ 130 VDC FF. 1.0 AOM
2.5 HP Treadmill Duty 6700 RPM 18 AMPS
1.5 HP Continuous Duty @ 95 VDC

I'm not looking to power my apartment (although that would be nice) so I figure despite the High RPM rating I should still be able to get some moderate results from this generator. Can anyone comment on these specs?

 

[Resqueline]

That's a pretty powerful motor, it might very well be able to power an apartment..
I don't understand all of those spec's but I believe it'll produce 12V & good power even below 1000 rpm.
With big wings you may find you'll need to design in some kind of protection (like furling for example).

 

[Eufouria]

I'm now questioning whether I should use the generator in a vertical or horizontal oriented design. The winds in my neighborhood can get high, I would guess around 10-12 mph, but I think it would make sense to take advantage of the almost constant 3-4 mph breeze moving through.
I am a bit confused as to how the generator produces the voltage and current; if it is spinning at half its rated rpm will it be producing half its rated voltage and amperage, half its amperage and full voltage or full amperage at half voltage?

 

[Resqueline]

At half speed it'll produce half the voltage but will still have the potential to deliver the full amperage.
The current is limited only by the magnet strength (+ the wiring resistance at very low voltages) so the windings may or may not overheat before the magnets "give up".
Vertical designs are usually low-rpm so that may neccessitate gearing. I don't have any practical experience with wind generators though.