Voltage and Amp Equations - Help

[jeraklidis]

I'm looking for accurate equations on calculating voltage from the number of turns, the number of coils, magnet strength, number of magnets,RPM etc.... Also the current at any given RPM. I can figure the amount of power in the wind I'm just curious if some one can provide the Generator side of things. The reason being is is that I haven't found an online calculator/graph utility that can take these values simulate turbine performance. If I get these equations I will create online simulation software that everyone can use for free. Here is a sample of what the charts would look like. http://demo.componentone.com/ASPNET/ControlExplorer/C1WebChart/LineCharts.aspx
If you are the master of the generator side just reply with equations and can I will take care of the rest (senior year computer science major). I have blade performance equations so i will include those as well. If you know Slot Pole combination equations, clogging torque equations (iron core), and any other losses you can think of (I^2R) I will pile in this thing and all you will have to do is press buttons and enter numbers... personally I think it will be useful. Thanks!

[WindJuggler]

Hello,

You can calculate all this and an app would be really nice. However you need to take in consideration all the variables.
Here is a link explaining a few aspects:

http://hyperphysics.phy-astr.gsu.edu...farlaw.html#c1

The general formula is V_gen = -N (dB dA)/dt
Where N stands for number of turns
B = the strength of the field in Tesla
dA over dt can be represented as the speed the with which the magnets move over the coil.

To calculate B is harder. There are some formulas here: http://instruct.tri-c.edu/fgram/web/Mdipole.htm.
But there are a lot of variables that play a role in it:

• magnet shape
• distance between the magnets
• Material used to place the magnets on(disc)
• use of double or single rotor
• distance between the rotors

There are probably a lot more.
I hope this helps a little bit. If you can make this app you would help a lot of people.

Wim

[Flux]

Yes if you can calculate the flux you can calculate the voltage. The next step is to calculate the effective resistance. The difference between emf and battery volts is the voltage forcing current through that effective resistance. Having got the current and battery volts you have power out.

If you can calculate efficiency you can then equate it to prop available power. Axial flux alternators are fairly predictable but with iron cored machines you have the leakage reactance to factor in and it gets very tricky.

Even with axial machines the calculated resistance doesn't work out, the things behave as though the effective resistance is about 1.3 times the true value but the factor is one of those " variable constants" that tend to crop up in fluid dynamic problems.

The efficiency seems to work out using the true resistance rather than the 1.3R value.

Flux is tricky but as a rough guide it will be about half Br for an axial machine where the air gap is about 1.5 times magnet thickness.

Don't forget that you need the rectified dc mean emf value not the rms emf between a pair of wires.

If you formula predicts 1v rms per phase, it will be 1root 3 volts line and the mean emf will be times 1.4  so you multiply by 1.73 and then 1.4.

You will have errors from waveforms but the results work out reasonably well, the phase volts may be a fair bit off a sine wave but with star connected machines the line volts are fairly good as the odd harmonics cancel.

Flux

[jeraklidis]

Flux I like the model you propose. Do you have algebraic/calculus formulas to take it through each step? I'm amazed that flux is half with an airgap 1.5 times magnet width. Exponentially I would expect the br to be worse. I know back Iron thickness does affect flux but I also heard you can increase the length of the back iron and decrease the width without clamping flux. If you'd like to email me at jeraklidis(at)yahoo(dot)com I will complete the project with printable graphs that return in pdf format. It doesn't have to be so indepth like Infolytica (http://www.infolytica.com/) but I know everyone here would benefit. Imagine changing the number of turns in an edit box and all the power graphs automatically update themselves. I can't do this without the help of you guys and I know its asking for someone or a group to jump on the grenade and say step one

If we want the Number of Turns we use Faraday's equation thus

Nturns = Volts * (( mag teslas * mag area) /rpm)

thus if Volts are changed from say 24v to 48v then the calculation wil change the number of turns needed per coil. Then we calculate resistances then from the number of turns and coil size we use the rpm to calculate amps .... etc

or

q =  Slots/ (2 * poles * phases) and start figuring out if a concentrated wire design will work with that combination slot pole combination or how it will need to be wound.

etc
etc

It wont be easy but if you have some free time feel free to email me and I'll work on it.

[jeraklidis]

I just figured out what you ment by multiplying (3)^(1/2) for the line voltage since its in a Wye configuration... anyways for anyone who emails me just make it strait algebra/calculus and then step instructions like
1.
2.
3.

etc  and its a tool as apposed to another person asking the same questions again and again.