Motor speed

Hi friend i m making a wind generator from which i expect 12v output so which generator should use ac or dc? Plz can u tell me how to construct circut dia.?If dc generator i use then how to give input to battery?

You get a GA from me for accurately proposing the OP real problem instead of his initial problem.

I do have one warning for the OP though. There will be an upper limit that your windmill and alternator can successfully spin without damage. To answer this will require an understanding of several mechanical engineering factors involving; i.e. bearing loads, wind loading on your vanes, mast support. I'm certain that I did not cover everything.

Out Put in Watts?

it means what ?

The syn. rpm as u must be knowing is given by N=120*/p.There is some thing called slip in Insuction motors ie the rotor lags the rotating magnetic field.The speed at which this runs is dependent on the load inertia and can be determined by superimposing the load torque - speed curve on the motor speed Torque curve and the point of intersection gives the actual speed.I presume u are ref. ti induction motor because other types are specifically mentioned.

If you take the PM DC generator- the output voltage will be RPM dependant hence for your variable speed it is almost ruled out.

For the field controlled DC generator, you may goo to a bit complicated excitation with the feed back for getting the voltage to your requirement. I think the automobiles may be working on this principle- since irrespective of engine RPM they do the charging.

If it is AC it is just a bit easier since now you can have the controlled rectifiers to do the work.

But only 12V charging by wind? at what ampere? looks like a homework project.

Before you read my posting here take note of my brief comments in reply to redfred's excellent comments in the thread on "Just a little bit of Help" regarding transformers and judge accordingly........

"Yes" for DC motors, "no" for AC induction and synchronous motors.

AC motor speed depends on the frequency of the AC current. (universal motors excepted) Under load they do drop speed a few percent but that amount is quite dependent on the motor design.

DC motor voltage is largely speed dependent if you take into account the loading. At no load the motor runs a certain rpm per volt. This is referred to as the "back EMF constant". Run the motor as a generator and every 1000 rpm will profuce another fixed amont of voltage. So if you know or can measure the back EMF constant of the DC motor you can use it as a tachometer. High quality coreless (sometimes called "Can" motors) used in instruments or servomechanisms often have the back EMF constant as one of the specs. Or you can calibrate a DC motor by running it with an AC motor you know the speed of.

Since electricity is still magic to me I can't guarantee any of this since I blew up my DVM last year.

Ed Weldon

Well thank you Ed for your kind words.

I did deliberately not say "AC no, DC yes" specifically because the OP just might be using a universal motor with an AC power source. You are also right on the money about brushed DC motor when working as a motor will track voltage to angular rotation. I particularly wanted the OP to realize that in most cases nothing about the motor and driver circuitry will prevent the motor from moving faster by an external force. However, a caveat should be added to the comment that angular velocity of an induction motors is set by the frequency applied. Look at the NEMA rotor standards, particularly the polyphase motor design D. This motor design will be most susceptible to mechanical load affecting angular velocity.

The input (mechanical ) power is a function of the wind linear velocity, turbine type and turbine diameter. This input power (torque * angular speed) is applied to the shaft of the generator. Considering the efficiency of the generator, you get the output power (electrical). If you are using a synchronous generator, the output voltage, which depends on the rotational speed (RPM) and the excitation current, can be regulated via the excitation, such that it should remain relatively constant for a wider range of RPM (the lower RPM limit is determined in order to cover the losses (mechanical and electrical) in the system, while the upper limit is dictated by mechanical stress). Since the generator output voltage has a frequency that is dependent on the RPM, it has to be rectified and as DC can be stored in a battery. If the load has to be fed in AC, a DC/AC converter is required. What voltages are to be used depends on the AC load and based on that the number of batteries connected in series.