Where the OVERUNITY using INDUCTION COILS comes from (eg Joule Thief)

[antijon]

Is impedance the same in these two cases?
Are you sending current through a coil,that produces a magnetic field-or are you  sending a magnetic field through the coil,that induces a current ?.

Brad

I really don't know. I'm assuming that the reactance is a part of the circuit because internal resistance is viewed as being in series with the load. I know that if you're load is only resistive, it won't change the power factor of the generator, so I'm not saying that the inductance causes a lag in current. I'm saying that as frequency increases, leakage flux of the generator coil will cause a decrease in EMF.

I'm going out on a limb here, but when you load a generator the output drops. This drop is proportional to the current and the leakage flux of the coil. A typical generator ramps up the motor to maintain 60hz, but it also has to increase the exciter current to maintain output voltage.

I guess what I'm saying is, if you tried to turn a 60hz generator faster, while keeping the exciter current and the load the same, you would actually see a drop in output voltage and current.

[citfta]

I really don't know. I'm assuming that the reactance is a part of the circuit because internal resistance is viewed as being in series with the load. I know that if you're load is only resistive, it won't change the power factor of the generator, so I'm not saying that the inductance causes a lag in current. I'm saying that as frequency increases, leakage flux of the generator coil will cause a decrease in EMF.

I'm going out on a limb here, but when you load a generator the output drops. This drop is proportional to the current and the leakage flux of the coil. A typical generator ramps up the motor to maintain 60hz, but it also has to increase the exciter current to maintain output voltage.

I guess what I'm saying is, if you tried to turn a 60hz generator faster, while keeping the exciter current and the load the same, you would actually see a drop in output voltage and current.

Hi antijon,

The parts of your post I highlighted in red are incorrect.  I believe you may be confusing auto alternators which vary in speed all the time to portable generators which usually run at a fixed speed controlled by the governor.  I am pretty sure I already posted about that is this thread but maybe you missed that post.

A portable generator only has to increase the fuel to the engine to maintain the same speed that it needed to keep the voltage at 120 vac or so and the frequency at 60 hz.  It does not need any increase in exciter current.  In fact there is no way for the exciter current to be increased as it is usually supplied by the residual magnetism in the armature and the windings of the armature.  Of course since an auto alternator is constantly changing speed it has to have a system in place to maintain the output voltage under those changing conditions.  So it does adjust the exciter current to do this. 

You are also incorrect about the voltage and current dropping if you increase the speed of a 60 hz generator.  If you increase the speed of a normal 60 hz generator and the load is not reactive then both the current and the voltage WILL increase.  Voltage is determined by the speed of the magnetic field passing the generating coils.  Current is determined by the load and the available torque to maintain the speed.  As the current increases the torque must increase to handle the extra load placed on the generating power source.  Of course you can overload the generator which will cause a drop in voltage as the current goes up.

I am not sure where you got the idea that increasing frequency causes an increase in flux leakage.  Can you give some source for where you saw that so I can check out that idea?

Respectfully,
Carroll

[tinman]

Below are a couple of scope shot's,along with test circuit.

The first scope shot shows results of slow pass of magnet over the coil.
The second scope shot shows a faster pass of the magnet over the coil.

Brad

[antijon]

Hey Carroll,

I can assure you I'm not referring to an automotive alternator, even though it is practically the same, except being 3 phase.

All types of generators have some type of exciter controller. Low exciter current results in low output voltage, and high for high. You may be referring to a brushless type, but that has a way of automatically increasing exciter current, depending on load.

You're probably right that I'm wrong about the decrease in EMF with frequency. I've read about synchronous impedance, armature reaction, and armature leakage flux. I know that losses increase with current, which will limit the output, but I can't find anything about frequency. I'm guessing that's because no one has ever tried turning a 60hz generator at 50,000 rpm. Lol

[itsu]

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