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 mbrownn Gold Member Join Date: Jan 2011 Posts: 1,637
A very thought provoking set of questions.

Can you get a gain from an inductive spike?

Of course you have to do some work to create a spike and the return is less than what you did to create it under ohms law. The thing is, both the work you put in and the return spike both create magnetism which can do work. Now the question is this. Is the energy in the work done by the magnetic field more than or less than the initial work put in?
If you make the magnetism do work does that reduce the power of the return spike?
Is the work done by magnetism and the return spike more than the power you put in? I believe it is.

Using maths it would suggest that the energy available in the magnetism of the input and return spike is double the input less what is lost to ohms law, but the moment we start making that magnetism do work our return spike reduces. This may be a disappointment but the reduction does not appear to be proportional. Why is this? because the magnetism is at 90 degrees to the current doing the work. I figure that the power available is the line (Hypotenuse) going between the input and the work done. Im not very good at explaining it but its like reactive power being added tangentially to the input power.

Can you get a gain from a transient spike?
This is interesting because no spike is truly transient, so the answer must be yes. How much? I dont think there is a lot to use directly but there may be benefits in translating them through a battery.

Can you get a gain from the change in flux from a magnetic field if you do NOT "pay" for the change?
Yes. I assume this relates to the collapse of the field and your first question.

Can electrical energy be trapped or stored in a coil?
I dont think so, I believe a coil to be a translation device that takes one form of energy and turns it into another.

The lockridge device may be an interesting model on which to test these points.
By passing a current through the coils a magnetic force rotates the armature. The moment the current is cut off the coils provide a spike which if given a path, allows current to continue flowing in the same direction. This current also provides a magnetic field and continues to rotate the armature. 2 for one less ohms law.
This current flow can also be collected in a capacitor. 3 for one less ohms law.
But is the energy in parts 1, 2 and 3 real? yes. The initial current did work so the inductive kickback current must be new and not stored energy in a conventional sense.

The initial current after it has passed through the coils can be stored in a capacitor or battery. The energy in it is equal to the input less ohms law.

As the coil has done work the inductance changes so the output from the inductive kickback is not what you would expect from a free coil doing no work, however; current does flow and a magnetic field is created which also does work and this second current can also be stored in a battery or capacitor.

If you use a capacitor to store energy, half the energy is lost due to efficiency. Much better to use a battery or use the current directly but that isnt always possible.

If our motor is 40% efficient at producing mechanical work, and we gain 30% from the inductive kickback we end up with a 70% efficient motor. This is exactly what happens when using a Universal motor on PWM provided the frequency is correct and the duration of the pulse is less than 60% I think this proves point 1.

The energy that passed through the motor and is stored in a capacitor can be anywhere from 30 to 70% of the input. If the mechanical efficiency is 70% then it should be impossible to get more than 30% in the capacitor.

Inductive kickback alone produces 15 to 17% which allowing for capacitor efficiency is 30 to 34% which when added to the mechanical is 100% so where has ohms law gone? We do get heat so ohms law is still there and we are over 100%.

I could go on but there is a lot to think about there.

Hope this gets you thinking __________________