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Inductor- amps vs volts

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Njguy

Member
From my understanding to increase the strength of an inductor/ electromagnet you either increase the number of turns of wire or the amperage. So in theory a 5 amp electromagnet at 10 volts should have the same strength as a 5 amp electromagnet at 120 volts. Assuming that the number of turns remains the same, correct?

This brings me to my real question. Generators slow down with increased electrical load because their coils produce an opposing magnetic field which slows down the rotor with a counter torque. So why don't generators simply generate a high voltage/ low amperage output and then send that to a transformer which then lowers the voltage and increases the amperage away from the generator? Wouldn't this give you the same power that you wan't whilst producing a lower load on the generator? Perhaps this is done already or I'm misunderstanding something.
 

crutschow

Well-Known Member
Most Helpful Member
You need to consider the conservation of energy. The load on the generator is determined by its power output (VA) so changing the output voltage of the generator has little effect on the shaft power required.

Note that you have to increase the number of winding turns to increase the voltage (which reduces the current) but this means the ampere-turns and the magnetic field stay essentially constant. Your initial premise of "assuming the number of turns remains the same" is not valid for a generator.
 

Njguy

Member
Note that you have to increase the number of winding turns to increase the voltage (which reduces the current) but this means the ampere-turns and the magnetic field stay essentially constant. Your initial premise of "assuming the number of turns remains the same" is not valid for a generator.

I understand what you are saying but wouldn't the rotor not slowing down under load (thus requiring more drive torque to maintain voltage) add to efficiency?

As for the windings, what about using a material that is less conductive? I guess the proper question is, is there a way to reduce current efficiently without increasing the winding's.
 
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Ratchit

Well-Known Member
Njguy,

"From my understanding to increase the strength of an inductor/ electromagnet you either increase the number of turns of wire or the amperage. So in theory a 5 amp electromagnet at 10 volts should have the same strength as a 5 amp electromagnet at 120 volts. Assuming that the number of turns remains the same, correct?"

No, electrical components are not measured by strength. No one would know what you mean if you said that one resistor or capacitor is "stronger" than the other. The two inductors you describe would have the same magnetomotive force.

"This brings me to my real question. Generators slow down with increased electrical load because their coils produce an opposing magnetic field which slows down the rotor with a counter torque. So why don't generators simply generate a high voltage/ low amperage output and then send that to a transformer which then lowers the voltage and increases the amperage away from the generator? Wouldn't this give you the same power that you wan't whilst producing a lower load on the generator? Perhaps this is done already or I'm misunderstanding something. "

You are not going to cheat physics. For instance, I can energize a motor with line voltage and measure low current existing through the motor when it is running idle. Then I can put a light load on the motor so it works harder, but doesn't slow down. The voltage and current are the same as before, but a wattmeter shows the motor is using more power. What gives? The answer is that the motor changes the phase relationship of the voltage and current so that both are more in phase with each other, thereby using more power. If I increase the load so that the motor slows down, then I can expect more current to be used in addition to closer voltage-current phase alignment.

Ratch
 
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Njguy

Member
Njguy,

No, electrical components are not measured by strength. No one would know what you mean if you said that one resistor or capacitor is "stronger" than the other. The two inductors you describe would have the same magnetomotive force.
Ratch

I did not say resistor or capacitor, I said electromagnet. The word strength is used all the time in referring to electromagnets as it is obviously a reference to the generated field. So if you could stop splitting hairs that would be great. It doesn't make you look smarter.
 

Ratchit

Well-Known Member
I did not say resistor or capacitor, I said electromagnet. The word strength is used all the time in referring to electromagnets as it is obviously a reference to the generated field. So if you could stop splitting hairs that would be great. It doesn't make you look smarter.

When all is said and done, an electromagnet is an inductor. An inductor, or electromagnet if you wish, does not have an intrinsic "strength". Its magnetic field is determined by how much many turns it has and the current you can pump through it. That is basic knowledge whose mastery that does not make anyone smarter. No one says that one resistor is hotter than another because it resistance is higher and it can accomodate more current.

Anyway, I hope you realize that electrical energy generation and transmission has a lot of aspects that have to be considered.

Ratch
 

crutschow

Well-Known Member
Most Helpful Member
I understand what you are saying but wouldn't the rotor not slowing down under load (thus requiring more drive torque to maintain voltage) add to efficiency?
Why do you think the rotor would not slow down? The torque required by the rotor does not change with a difference in the voltage as long as the VA (power) is constant.
As for the windings, what about using a material that is less conductive? I guess the proper question is, is there a way to reduce current efficiently without increasing the winding's.
What material is less conductive? No you can't reduce current without increasing the number of windings to increase the voltage.

I'm afraid there's no way to significantly increase the efficiency of a generator that hasn't already been thought of. The efficiency of large AC generators is already greater than 90% so there's really not much room for improvement.
 

dr pepper

Well-Known Member
Most Helpful Member
If a generator lights a lamp, the energy from the mechanical source turning the gen lights the lamp, plus a little energy in the ineffeciency of the generator, it makes little difference whether the lamp is 3v or 300v, the amps x the volts is the same for any 2 lamps of the same wattage, and the torque on the gen the same(so the amount it slows down the same).

If you used a conductor with higher resistance in the generators windings unforetunately the efficicency would go down, as energy would be lost as heat in the resistance of the windings.

I dont think it will be that easy to find a new trick way of generating power though it may be possible.

To answer your question of effeciently reducing current, that can be done in 2 ways, with dc you can use pwm, and ac is simpler you could just use a choke, allthough both methods would introduce small losses.
 
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