Wind Power B/C

[samlan16]

Chalker (or anyone else that would like to chime in), we have been debating this idea for a while, but why is resistance is included in the circuit? Won't the turbine that spins the fastest ALWAYS produce the greatest output?

In the event that someone's turbine generates a huge current, the resistor acts to prevent the voltmeter from being damaged. Mostly a precaution in that sense.

[chalker]

Chalker (or anyone else that would like to chime in), we have been debating this idea for a while, but why is resistance is included in the circuit? Won't the turbine that spins the fastest ALWAYS produce the greatest output?

In the event that someone's turbine generates a huge current, the resistor acts to prevent the voltmeter from being damaged. Mostly a precaution in that sense.

Not really. Having the resistor in the circuit is really important for a fundamental reason: it’s ensures you are measuring actual generated current, not transient ones. Multimeters have an internal resistance of several mega-ohms (often between 1 and 10 Mohms). To be clear, schematically you have:
_______________
| | |
Vg R M
|______|_______|

Where Vg is the voltage from the Generator, R is the resistor, M is the multimeter resistance

If R isn’t present, Ohm’s law states:
Vg=I*M
75mV=I*5Mohms
I = 15 nA

If R is present, Ohm’s law essentially allows us to ignore the large resistance of the multimeter and results in:
Vg=I*R
25mv=I*5ohms
I = 5 mA

15 nA is really small. Stray magnetic fields from say an AC power cord positioned to close to the device could easily induce currents of that size in the wires. This is also why we want to have the resistor as small value as possible.

[JonB]

Chalker (or anyone else that would like to chime in), we have been debating this idea for a while, but why is resistance is included in the circuit? Won't the turbine that spins the fastest ALWAYS produce the greatest output?

In the event that someone's turbine generates a huge current, the resistor acts to prevent the voltmeter from being damaged. Mostly a precaution in that sense.

Not really. Having the resistor in the circuit is really important for a fundamental reason: it’s ensures you are measuring actual generated current, not transient ones. Multimeters have an internal resistance of several mega-ohms (often between 1 and 10 Mohms). To be clear, schematically you have:
_______________
| | |
Vg R M
|______|_______|

Where Vg is the voltage from the Generator, R is the resistor, M is the multimeter resistance

If R isn’t present, Ohm’s law states:
Vg=I*M
75mV=I*5Mohms
I = 15 nA

If R is present, Ohm’s law essentially allows us to ignore the large resistance of the multimeter and results in:
Vg=I*R
25mv=I*5ohms
I = 5 mA

15 nA is really small. Stray magnetic fields from say an AC power cord positioned to close to the device could easily induce currents of that size in the wires. This is also why we want to have the resistor as small value as possible.

Thank you for the explanation- that clears much of it up. I am not sure if your 'Not really" response was directed at me or the other response so I will ask anyway. Would it be a fair conclusion that if you had two turbines spinning (assuming the air from the fan is identical and both have the same resistance within the circuit) then the turbine spinning faster will always output a greater voltage? This is how I understand this event but correct me if I am wrong.

[chalker]

Would it be a fair conclusion that if you had two turbines spinning (assuming the air from the fan is identical and both have the same resistance within the circuit) then the turbine spinning faster will always output a greater voltage? This is how I understand this event but correct me if I am wrong.

Generally yes. There are caveats / special situations of course though that might make this not so. The basic physics behind this is Faraday's law of induction (https://en.wikipedia.org/wiki/Faraday's ... _induction), which can be stated as:
"The induced electromotive force in any closed circuit is equal to the negative of the time rate of change of the magnetic flux enclosed by the circuit"

There are a lot of big words there, but it can essentially be summarized as: The voltage in a generator circuit is equal to the frequency of the changes in the magnetic field in the generator. Hence the faster you turn the generator, the higher the frequency you are creating and the higher the voltage.

[barringtonscioly]

Can we use CD dividers instead of CDs? They still mount on the standard CD mount...

[JonB]

Can we use CD dividers instead of CDs? They still mount on the standard CD mount...

No. Only compact disks (CDs).

[chalker]

Did anyone have any luck with the blade assembly found on ward's science?

FYI, I've been informed there was an issue with the cd mount hubs they were sending out. Customers will receive new ones in the very new future.

[dragon-fruit35]

Anyone have a link to a cd motor that works for this?

[soyuppy]

For those who's interested in how to get a CD motor to test your blade.

1. Get a used portable CD player from e-bay. The cheaper the better. Look for Memorex or Phillip. They can be had for less than 20.00
2. Pry open the use CD Player yank out the CD Motor. This will give you a CD Motor with the attachment that can be snap to the CD blade.
- Whie doing rigurous testing on the CD Motor, it can get busted due to constant spinning in both direction(CW/CCW).
3. Get replacement motor from Amazon. http://www.amazon.com/gp/product/B00OTC ... ge_o04_s00. This only come with motor. Reuse the attachment from the original CD player motor. 2 motors for 4 buck is much better deal. You can order several set of these just to have them ready if any get busted

Hope this helps

[soyuppy]

Can anyone clarify the scoring rule?
Rule 5f: 15 pts penalty apply for any construction violation or miss impound
Rule 5g: Power Score = 0 for unsafe operation/modify CD or fail to bring blade assembly

If the team has no blade, then there's nothing to impound. But the team is allow to take the written exam. Does this mean the team get 0 pts along along with -15 pts penalty apply to the written exam?